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Links to other websites will open in new windows. Most browsers have a "find" feature (usually activated by pressing and holding the "Ctrl" and "F" keys together) which may help you search for a specific word on this page. Some of these entries contain direct quotes from their cited sources. Some of the Greek letters and symbols on this page may not appear correctly on some computers.
| Abnormality | In meteorology, a deviation of the weather or climate from the conditions normally expected at a particular time and place; a deviation from the normal (amsglossary.allenpress.com). |
| Absolute Altitude | The true vertical distance above the terrain (amsglossary.allenpress.com). |
| Absolute Extremes | Highest or lowest temperature observed over the whole period of observation (amsglossary.allenpress.com). |
| Absolute Humidity | In a system of moist air, the ratio of the mass of water vapor present to the volume occupied by the mixture; that is, the density of the water vapor component (amsglossary.allenpress.com). |
| Absolute Instability | The state of a column of air in the atmosphere when it has a superadiabatic lapse rate of temperature that exceeds the dry-adiabatic lapse rate (amsglossary.allenpress.com). |
| Absolute Stability | The state of a column of air in the atmosphere when its lapse rate of temperature is less than that of the saturation-adiabatic lapse rate (amsglossary.allenpress.com). |
| Absolute Zero | The zero point of the Kelvin temperature scale, of fundamental significance in thermodynamics and statistical mechanics (amsglossary.allenpress.com). |
| Absorbed Solar Radiation | Solar radiation absorbed by the atmosphere's constituent gases, suspended material, clouds, or by the earth's surface (amsglossary.allenpress.com). |
| Absorptance (α) | Ratio of the amount of energy absorbed by a material to the total radiation incident on the material. Usually represents a measured quantity (Roberts 2007). |
| Absorption Coefficient (α) | A measure of the extinction due to absorption of monochromatic radiation as it traverses a medium, generally with units of 1/distance (amsglossary.allenpress.com). |
| Absorption Spectrum | The detailed dependence on wavelength of the intensity of radiation absorbed by a given medium (amsglossary.allenpress.com). |
| Absorptivity (α) | The fraction of incident radiation that is absorbed by matter. Absorptivity may at times be a function of wavelength and/or direction, and is related to the emissivity of the region by Kirchhoff's law. The absorptivity is identically equal to unity for blackbodies and is independent of wavelength for gray bodies (amsglossary.allenpress.com). It is similar to absorptance, but usually represents an intrinsic property of a material (Roberts 2007). |
| Acclimation | Adaption of living organisms to all aspects of an environment (amsglossary.allenpress.com). |
| Accretion | In cloud physics, usually the growth of an ice hydrometeor by collision with supercooled cloud drops that freeze wholly or partially upon contact. |
| Acid Deposition | The accumulation of an acidic chemical from the atmosphere to the surface of the earth, or to plants and structures at the surface (amsglossary.allenpress.com). |
| Acid Fog | The presence of considerable levels of acidic material within fog. The material has been taken up from the gas phase which results in pH values that are less than approximately 3 in the liquid phase (amsglossary.allenpress.com). |
| Acid Pollution | Chemicals not occurring naturally in the atmosphere that either are acidic, or that easily react or dissolve in water to become acidic (amsglossary.allenpress.com). |
| Acoustic Backscattering | Scattering of sound or ultrasound in the direction of the source (amsglossary.allenpress.com). |
| Acoustic Dispersion | The separation of a sound wave into its frequency components as it passes through a given medium (amsglossary.allenpress.com). |
| Acoustic Echo Sounding | Measuring the depth of the ocean by determining the time required for the echo of a sound impulse to return to a point near the surface (amsglossary.allenpress.com). |
| Acoustic-gravity Wave | A wave disturbance with restoring forces such as buoyancy and the elastic compressibility of the fluid medium (amsglossary.allenpress.com). |
| Acoustic Imaging | The use of acoustic energy to form a representation of a physical object, such as side-scanning sonar imaging of objects on the ocean bottom (amsglossary.allenpress.com). |
| Acoustic Intensity | Usually expressed in watts per square meter, acoustic intensity is the average acoustic power transported across a unit area (amsglossary.allenpress.com). |
| Acoustic Radar | Use of sound waves with radar technology for remote probing of the lower atmosphere, up to heights of about 1500 m, for measuring wind speed and direction, humidity, temperature inversions, and turbulence (amsglossary.allenpress.com). |
| Acoustic Rain Gage | An instrument designed to determine rainfall over lakes and oceans (amsglossary.allenpress.com). |
| Acoustic Refraction | The change in the direction of sound as it travels through a medium due to differences in physical and chemical characteristics of the medium (amsglossary.allenpress.com). |
| Acre-foot | The volume of water that is represented by a depth of 1 foot over an area of 1 acre (amsglossary.allenpress.com). |
| Adhesion Efficiency | The fraction of ice particles that collide with the collector ice particle and adhere to it (amsglossary.allenpress.com). |
| Adhesive Water | An attraction between water and soil that results in water retention within soil (amsglossary.allenpress.com). |
| Adiabatic Atmosphere | The vertical extent of a model atmosphere that is characterized by a dry-adiabatic lapse rate (amsglossary.allenpress.com). |
| Adiabatic Equilibrium | The hydrostatic equilibrium of temperature and pressure in a vertical distribution. With adiabatic equilibrium an adiabatically displaced air parcel continues to possess the same temperature and pressure as its surroundings. |
| Adiabatic Process | A process in which a system does not interact with its surroundings by virtue of a temperature difference between them. Any change in internal energy (for a system of fixed mass) is solely a consequence of working. For an ideal gas and for most atmospheric systems, compression results in warming, expansion results in cooling (amsglossary.allenpress.com). |
| Adiabatic Temperature Gradient | The rate of change of temperature that is dependent on the pressure under adiabatic conditions (amsglossary.allenpress.com). |
| Advanced Very High Resolution Radiometer | Used in meteorology and oceanography, it is a sensor carried onboard NOAA satellites to measure cloud cover and sea surface temperature. (Abbreviated AVHRR) (amsglossary.allenpress.com). |
| Advection | The process of transport of an atmospheric property solely by the mass motion of the atmosphere; also, the rate of change of the value of the advected property at a given point (amsglossary.allenpress.com). |
| Advection Fog | A type of fog caused by the advection of moist air over a cold surface, and the consequent cooling of that air to below its dewpoint. A very common advection fog is that caused by moist air over a cold body of water (sea fog) (amsglossary.allenpress.com). |
| Advection Frost | The occurrence of frost as a result of the horizontal transport (advection) of a cold air mass with air temperature below 0°C. This type of frost is responsible for causing damage to agricultural areas of south Florida and the Rio Grande Valley of Texas during cold polar outbreaks (amsglossary.allenpress.com). |
| Advective Change of Temperature | The contribution to local temperature change that is caused by the horizontal or vertical advaction of air (amsglossary.allenpress.com). |
| Aeolian | Derived from the name of the Greek god of the winds, aeolian pertains to the effect of the wind (amsglossary.allenpress.com). |
| Aerial Perspective | The reduced contrast of distant objects that is caused by airlight (amsglossary.allenpress.com). |
| Aerial Photograph | A photograph of the Earth's surface taken (either directly downward or obliquely) from an airplane (sdc.ucsb.edu). |
| Aeronautics | The techniques involved in the art or science of flight. |
| Air | Mixture of gases forming the earth's atmosphere, consisting of nitrogen (∼78 percent), oxygen (∼21 percent), water vapor, and other trace gases such as carbon dioxide, helium, argon, ozone, or various pollutants (amsglossary.allenpress.com). |
| Airborne | Generally meaning aircrafts or sensors that do not orbit the earth. |
| Airborne Particulates | Solid particles suspended in the air (amsglossary.allenpress.com). |
| Airmass (m) | A widespread body of air, with properties that can be identified as 1) having been established while that air was situated over a particular region of the earth's surface (airmass source region), and 2) undergoing specific modifications while in transit away from the source region (amsglossary.allenpress.com). It is the relative distance standardized to the thickness of the total atmospheric column. Increases as a function of the sec(θ). A value of 2 airmasses occurs at θ = 60 degrees. Modifies optical thickness off nadir (Roberts 2007). |
| Air Parcel | An imaginary small body of air a few meters wide that is used to explain the behavior of air (Ahrens 2007). |
| Air-Sea Interaction | The processes that occur as a consequence of the air being in contact with the sea surface, and that affect the dynamics and thermodynamics of the air and water boundary layers (amsglossary.allenpress.com). |
| Air temperature | A measure of the average kinetic energy of air molecules, usually referring to the quantity that would be measured by a thermometer exposed to the air but sheltered from direct solar radiation. Surface air temperature is usually measured at a standard height of either 1.5 or 2 meters above the ground (Ahrens 2007). |
| Albedo | The percent of energy reflected by an object to the amount incident upon it, integrated across all wavelengths and angles. Albedo is source dependent, and typically refers to solar albedo, which is the percent of incident solar radiation that an object reflects (Ahrens 2007; Roberts 2007). |
| Albedometer | An instrument used for the measurement of the reflecting power (the albedo) of a surface (amsglossary.allenpress.com). |
| Alluvial | Geologic layers deposited by streams (amsglossary.allenpress.com). |
| Alpine Tundra | A form of tundra in which the absence of trees is due to high altitude instead of high latitude (amsglossary.allenpress.com). |
| Altimeter | An instrument that determines the altitude of an object with respect to a fixed level (amsglossary.allenpress.com). |
| Altitude | A measure (or condition) of height, especially of great height, as a mountain top or aircraft flight level. In meteorology, altitude is used almost exclusively with respect to the height of an airborne object above the earth's surface, above a constant-pressure surface, or above mean sea level (amsglossary.allenpress.com). |
| Altocumulus | A principal cloud type (cloud genus), white and/or gray in color, that occurs as a layer or patch with a waved aspect, the elements of which appear as laminae, rounded masses, rolls, etc (amsglossary.allenpress.com). |
| Altostratus | A principal cloud type (cloud genus) in the form of a gray or bluish (never white) sheet or layer of striated, fibrous, or uniform appearance (amsglossary.allenpress.com). |
| Amplitude | Often the greatest magnitude at a given point of any spatially and temporally varying physical quantity governed by a wave equation; can also mean the spatial part of a time-harmonic wave function (amsglossary.allenpress.com). |
| Angle of Exitance (θe) | Angle between outgoing radiation and a vector normal to the surface (Roberts 2007). |
| Angle of Incidence (θ) | Angle between incoming radiation and a vector normal to the surface (Roberts 2007). |
| Angle of Refraction (θr) | The angle between the direction of propagation of an electromagnetic or acoustic wave (or ray) refracted by an optically homogeneous body and the local normal to that body (amsglossary.allenpress.com). The angle is measured perpendicular to a surface for radiation that has entered a medium with simple refractive index, n. Defined using Snell’s Law (Roberts 2007). |
| Angle of Total Internal Reflection | Angle at which all radiation is reflected when it strikes a discontinuity between two materials with differing refractive indices. Occurs only when radiation passes from a medium with a high simple refractive index to one with a lower one (Roberts 2007). |
| Angular Spreading | Spreading of waves in space due to differences in direction of wave propagation (amsglossary.allenpress.com). |
| Annual | A plant that germinates, grows, reproduces, and dies, all within a single growing season; compare to "perennial" (MacDonald, 2003). |
| Anomaly | The deviation of (usually) temperature or precipitation in a given region over a specified period from the long-term average value for the same region (amsglossary.allenpress.com). |
| Aperture | In a unidirectional antenna or other remote sensing device (such as a camera or telescope), that portion of the plane surface that is perpendicular to the direction of maximum radiation and through which the major part of the radiation passes (amsglossary.allenpress.com). |
| Aphelion | The point on the orbit of the earth (or any other body in orbit about the sun) that is farthest from the sun; the opposite of perihelion (amsglossary.allenpress.com). |
| Apparent Horizon | The line between the sky and the earth projected on the celestial sphere. This line is often irregular, due to the earth's topography. On flat surfaces, such as the sea or a level plane, the line approximates a great circle if the observer's elevation above the surface is insignificant and a small circle if the elevation is appreciable (amsglossary.allenpress.com). |
| Aquifer | A layer of saturated geologic materials that could yield water to springs or wells (amsglossary.allenpress.com). |
| Arctic Circle | The line of latitude 66°34′N. Along this line the sun does not set on the day of the summer solstice, about June 21, and does not rise on the day of the winter solstice, about December 22. From this line the number of twenty- four-hour periods of continuous day or of continuous night increases northward to about six months each at the North Pole (amsglossary.allenpress.com). |
| ARM | Atmospheric Radiation Measurement |
| Ash | Airborne particulates produced as a combustion product (amsglossary.allenpress.com). |
| ASOS | Automated Surface Observing System: a specific kind of high-quality surface weather station typically found at civilian airports. See NOAA (1998) to learn more. |
| Association | Refers to the idea that when finding a certain phenomena or activity, it is common to encounter related or associated features or activities; one of the terms that image interpreters commonly use to describe the relation of objects in remotely sensed imagery (Jensen 2007). |
| Astronomical Horizon | The great circle that is 90° from the local vertical. The astronomical horizon is usually more convenient to use than the apparent horizon (amsglossary.allenpress.com). |
| Astronomical Unit | The mean distance from the Earth to the sun. Approximately 92,957,210 miles (srrb.noaa.gov). |
| Atmosphere | The envelope of gases that surround a planet and are held to it by the planet's gravitational attraction. The earth's atmosphere is mainly nitrogen and oxygen (Ahrens 2007). |
| Atmospheric pressure | The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of mercury (Hg), or in hectopascals (hPa) (Ahrens 2007). |
| Autumnal equinox | The equinox (approximately 22 September) at which the sun crosses the celestial equator from the Northern Hemisphere to the Southern Hemisphere (amsglossary.allenpress.com). |
| AVN | The Aviation numerical weather forecast model |
| Azimuth (φ) | Angle measured horizontally from true north or true south (Roberts 2007). If a reference system defines true north to have an azimuth of 0°, with azimuth angles increasing in the clockwise direction, then true east would have an azimuth of 90°, true south would have an azimuth of 180°, and true west would have an azimuth of 270°. This is a commonly used reference system for expressing angles of azimuth, but other reference systems also exist (such as defining true south to have an azimuth of 0°). |
| Azimuth Resolution | The angle or distance by which two targets at the same range must be separated in azimuth to be distinguished by a radar (amsglossary.allenpress.com). |
| Backscatterer | An object that preferentially scatters radiation in the direction of incident radiation. Trees are backscatterers, as are many rough surfaces (Roberts 2007). |
| Backscatter Coefficient | A quantitative measure of the intensity of energy returned to a radar antenna from the terrain (sdc.ucsb.edu). |
| Band | A wavelength interval in the electromagnetic spectrum. For most remote sensing systems, such as MODIS, Landsat, GOES, AVIRIS, and others, the bands designate specific wavelength intervals at which images are acquired (sdc.ucsb.edu). In remote sensing, the terms "band" and "channel" generally mean the same thing. |
| Banking | 1. To laterally and inwardly tilt an aircraft in flight. |
| 2. What they do at Washington Mutual | |
| Beer-Bourget-Lambert Law | Law that describes the exponential attenuation of radiation traveling a distance, d, through an absorbing medium with absorption coefficient, α (Roberts 2007). |
| Bi-Directional Reflectance | Reflectance of an object in which incident and departing radiation are from a specific direction (Roberts 2007). |
| Bi-Directional Reflectance Distribution Function (BRDF) | Function that describes angular variation in reflectance as a function of azimuth and incidence for incident and reflected radiation (Roberts 2007). |
| Bi-Hemispherical Reflectance | Reflectance of an object in which incident radiation and departing radiation are integrated across all angles of azimuth and exitance. Also called spherical albedo (Roberts 2007). |
| Biogeography | The study of the past and present geographic distributions of plants and animals and other organisms and the environmental and evolutionary forces that produce those distributions (MacDonald, 2003). |
| Biomass | The mass of living material in an ecosystem. Generally considered the dried weight of all living matter in a prescribed area (MacDonald, 2003). |
| Blackbody | A theoretical object that is a perfect emitter and absorber (an object with an emissivity of 1 at all wavelengths). No object is a perfect blackbody, but an object can behave like a blackbody at one range of wavelengths and not at another. This is the case for water and snow, for example (Roberts 2007). |
| Blackbody Radiation | Radiation, especially its spectral distribution, from an ideal blackbody emitter (amsglossary.allenpress.com). |
| Blackbody Temperature | The temperature of a body that absorbs all radiation incident upon it (amsglossary.allenpress.com). |
| Bowen Ratio (β) | Ratio of Sensible Heat to Latent Heat. Used to simplify the energy budget when estimating heat exchange using gradient methods (Roberts 2007). The ratio of sensible to latent heat fluxes from the earth's surface up into the air (amsglossary.allenpress.com). |
| Brewster Angle | Angle at which parallel polarized radiation is not reflected by a smooth medium (Roberts 2007). |
| Brightness Temperature (Tb) | A descriptive measure of radiation in terms of the temperature of a hypothetical blackbody emitting exactly the same amount of radiation at the same wavelength (amsglossary.allenpress.com). The apparent temperature of an object at a specific wavelength is described by the inverse of the Planck equation (K) (Roberts 2007). |
| Brightness Value | Same as a digital number. The value assigned to a pixel in a digital image; this could represent radiance, reflectance, brightness temperature, or other information, but the DN values may not be very useful until they are converted into other units (sdc.ucsb.edu). |
| Calibration | A process that insures correct reading from an instrument by comparing the field instrument to a measurement standard (srrb.noaa.gov). |
| Canopy | The topmost area of vegetation cover (MacDonald 2003). This doesn't necessarily have to refer to tall trees: the tops of grasses or shrubs could also be called canopies. |
| CDC | NOAA's Climate Diagnostics Center |
| Celestial Equator | The projection of the plane of the geographical equator upon the celestial sphere (amsglossary.allenpress.com). |
| Celestial Sphere | The apparent sphere of infinite radius, having Earth as its center. It is upon the “inner surface” of this sphere that all heavenly bodies, the ecliptic, and the celestial equator appear. Disregarding the effects of topography and refraction near the horizon, for practical purposes half of this sphere may be considered visible from any point on the earth's surface at any time (amsglossary.allenpress.com). |
| Celsius (°C) | A unit of temperature defined such that pure ice melts at 0°C and pure water boils at 100°C at one atmosphere pressure (Roberts 2007). |
| Centerpoint | The optical center of a photograph (sdc.ucsb.edu). |
| Channel | A wavelength interval of an electromagnetic sensor. For most remote sensing systems, such as MODIS, Landsat, GOES, AVIRIS, and others, the channels designate specific wavelength intervals at which images are acquired (sdc.ucsb.edu). In remote sensing, the terms "band" and "channel" generally mean the same thing. |
| Chaparral | An ecological community containing shrubby plants that have adapted to dry summers and moist winters that occur especially in areas within southern California. |
| CIMIS | California Irrigation Management Information System |
| Climate | The accumulation of daily and seasonal weather events over a long period of time. |
| Colonization | The expansion of a species and its establishment of a self-sustaining population in a new geographic region (MacDonald, 2003). |
| Community | All the different populations of organisms that live and interact with each other within a prescribed area (MacDonald, 2003). |
| Community Type | The collection of species that is generally found in a specific type of habitat (MacDonald, 2003). |
| Conduction (G) | Transport of energy (charge) solely as a consequence of random motions of individual molecules (ions, electrons) not moving together in coherent groups (amsglossary.allenpress.com). Heat is transfered from molecular contact in response to a temperature gradient, in which molecules do not shift position (Roberts 2007). |
| Conifer | A plant with cones bearing gymnosperms, such as pines and spruces (MacDonald, 2003). |
| Contained | A wildland fire is considered contained when a fuel break around the fire has been completed. This break may include natural barriers or manually and/or mechanically constructed line; compare with "controlled" (inciweb.org). |
| Contrast Enhancement | Image-processing procedure that improves the contrast ratio of images. The original narrow range of digital values is expanded to utilize the full range of available digital values (sdc.ucsb.edu). |
| Contrast Ratio | On an image, the ratio of reflectances between the brightest and darkest parts of an image (sdc.ucsb.edu). |
| Controlled | A wildland fire is considered controlled when it is completely extinguished, including spot fires, and the control line has been strengthened so that any flare-ups or spot fires that may occur from within the perimeter of the fire, will not break through this line; compare with "contained" (inciweb.org). |
| Convection | Motions in a fluid that result in the transport and mixing of a fluid's properties. In meteorology, convection usually refers to atmospheric motions that are predominantly vertical, such as rising air currents due to surface heating. The rising of heated surface air and the sinking of cooler air aloft is often called free convection (Ahrens 2007). Convection can involve sensible heat transfer (molecular motion) or latent heat transfer (heat transfer by a change in phase) (Roberts 2007). |
| COPR | Coal Oil Point Reserve One of several locations containing weather equipment that is designed to collect information on relative humidity, leaf wetness, and wind speed. The strip of coastal land is just west of the UCSB campus and is home to a number of endangered species. |
| Crab | A manuever in aeronautics where an aircraft heads partly into the wind to compensate for drift. |
| Crab Angle | In air navigation, the angle between an aircraft's course and its heading required to maintain that course against the wind (amsglossary.allenpress.com). |
| Crown | The top of a tree or shrub, generally the part with clusters of leaves. |
| Curvilinear | Consisting of or containing curved lines; one of the terms that image interpreters commonly use to describe the shapes of objects in remotely sensed imagery (Jensen 2007). |
| Damping Depth (d) | Depth at which the amplitude of the temperature curve is reduced to e-1 (usually expressed in units of meters) (Roberts 2007). |
| Data logger | A device that generally provides the measurement and control functions of a data acquisition system. |
| Deciduous | Perennial plants that lose their leaves during annual cold or dry seasons (MacDonald, 2003). |
| Declination (δ) | 1. Declination usually refers to "solar declination," which is the latitude of the subsolar point (Roberts 2007). |
| 2. Magnetic declination (also called magnetic variation) is the angle between true north and magnetic north, which varies with geographic location (amsglossary.allenpress.com). If you know the magnetic declination for your area, you can use this to determine true north using a magnetic compass. For example, UCSB's geographic location gives it a magnetic declination of about 14 degrees east (so from the perspective of someone on the ground near UCSB, the magnetic north pole is about 14 degrees east of the geographic north pole). Thus, to get true headings (such as true north) for measurements made near UCSB, subtract 14 degrees from the headings read from a magnetic compass. Some compasses allow the user to align the pointer to be a certain angle away from the direction their magnetic needle is pointing, and setting that angle to the magnetic declination for the area will make headings read off the compass to be true headings, instead of magnetic headings. | |
| Density (ρ) | 1. Mass per unit volume (kg m-3) (Roberts 2007). |
| 2. The number of individuals of a given species per unit of ground area (MacDonald, 2003 ). | |
| DEMs | Digital Elevation Models |
| Dew point | The temperature to which air must be cooled (at constant pressure and constant water vapor content) for saturation to occur (Ahrens 2007). |
| Dielectric Constant (ε) | The square of the complex refractive index (N). Critical entity used in calculations of surface interactions in the microwave (Roberts 2007). The response of optically homogeneous matter to excitation by a time- harmonic electric field is frequency-dependent (amsglossary.allenpress.com). |
| Diffraction | Process in which electromagnetic radiation bends when it either passes through a slit or interacts with an object of a dimension similar to the wavelength. Diffraction allows us to hear around corners (Roberts 2007). |
| Digital Image | An image where the property being measured has been converted from a continuous range of analogue values to a range expressed by a finite number of integers, usually recorded as binary codes from 0 to 255, or as one byte (sdc.ucsb.edu). |
| Digital Image Processing | Computer manipulation of the digital-number values of an image (sdc.ucsb.edu). |
| Digital Number (DN) | The value assigned to a pixel in a digital image; this could represent radiance, reflectance, brightness temperature, or other information, but the DN values may not be very useful until they are converted into other units (sdc.ucsb.edu). |
| Directional-Hemispherical Reflectance | The albedo of a surface when illuminated from a single direction (amsglossary.allenpress.com). Incident radiation is from a specific direction while reflectance is integrated across all angles of azimuth and exitance. Also called planetary albedo (Roberts 2007). |
| Distortion | On an image, changes in shape and position of objects with respect to their true shape and position (sdc.ucsb.edu). |
| Disturbance | A discrete and relatively rapid physical or biological event that disrupts ecosystem, community, or population structure and changes resourcesm substrate availability, or the physical environment (MacDonald, 2003). |
| Doppler radar | A radar that determines the velocity of falling precipitation either toward or away from the radar unit by taking into account the Doppler shift (Ahrens 2007). |
| Doppler shift (effect) | The change in the frequency of waves that occurs when the emitter or the observer is moving toward or away from the other (Ahrens 2007). |
| Drift-correction angle | In air navigation, the angle between an aircraft's course and its heading required to maintain that course against the wind. Also called crab angle (amsglossary.allenpress.com). |
| Dry-adiabatic Lapse Rate | The rate of decrease in temperature with height of a parcel of dry air lifted by a reversible adiabatic process through an atmosphere (amsglossary.allenpress.com). |
| DST | Daylight Savings Time |
| Ecosystem | All of the interacting biological and physical components of a prescribed area (MacDonald, 2003). |
| Ecotone | The geographic boundary between two different adjacent communities (MacDonald, 2003). |
| Ecliptic | The apparent annual path of the sun around the earth that is seen as the great circle in the celestial sphere (amsglossary.allenpress.com). |
| Edge Enhancement | Image-processing technique that emphasizes the appearance of edges and lines (sdc.ucsb.edu). |
| E-folding distance | Distance at which energy is attenuated to a value of 1/e (Roberts 2007). |
| Endemic | Restricted to one geographic area (MacDonald, 2003). |
| Electromagnetic Radiation | Energy propagated in the form of and advancing interaction between electric and magnetic (sdc.ucsb.edu). |
| Electromagnetic Spectrum | Continuous sequence of electromagnetic energy arranged according to wavelength or frequency (sdc.ucsb.edu). |
| Elevation | A measure (or condition) of height, especially with respect to the height of a point on the earth's surface above a reference plane (usually mean sea level), as “station elevation.” (amsglossary.allenpress.com). |
| Emissivity (ε) | An object’s emissivity is a ratio of its emitted radiation to that of a blackbody at the same temperature, and can be considered in two different forms: spectral emissivity and all-wave emissivity. Spectral emissivity can vary with view angle but not temperature, and it depends upon an object’s chemical and physical properties. All-wave emissivity is spectral emissivity integrated over all wavelengths and view geometries, which can vary with temperature (Adams & Gillespie 2006; Roberts 2007). |
| Encoded Radiance | Measured radiance, represented by a quantized voltage output by a detector: these quantized numbers are stored as digital number (DN) values (Roberts 2007). |
| Energy Balance | The balance that exists between the net warming or cooling of a given volume, and all possible sources and sinks of energy. Sources and sinks of energy usually include net fluxes or sensible heat, latent heat, and radiant energy (amsglossary.allenpress.com). |
| Equation of Time | The difference at any instant between the apparent solar time and the mean solar time as measured at a specified place; it is the difference between the hour angles of the apparent sun and the mean sun (amsglossary.allenpress.com). |
| Equinox | Either of the two points of intersection of the sun's apparent annual path and the plane of the earth's equator, that is, a point of intersection of the ecliptic and the celestial equator(amsglossary.allenpress.com). |
| ESRI | Environmental Systems Research Institute (company that makes ArcGIS software) |
| Eta | A numerical weather forecast model |
| Evapotranspiration | The water lost in an area and added to the atmosphere, which is caused by a combination of the effects of evaporation from the ground and the transpiration from the vegetation (geographic.org). |
| Exitance (M) | Radiant flux departing from a unit area integrated over all possible angles of incidence (θ) and azimuth (φ), typically expressed in units of Watts per square meter (W m-2); also called Radiant Flux Density (Roberts 2007). |
| Extinction Coefficient (k) | Represents the fractional depletion of radiance per unit path length (amsglossary.allenpress.com). Unitless measure of the extent to which a material absorbs radiation. k = α*λ/(4π) (Roberts 2007). |
| Extinction Cross Section (σext) | Property of a material that describes the amount of energy intercepted and absorbed or scattered (m2). The extinction cross-section is the sum of an absorption and scattering cross-section (Roberts 2007). |
| Extinction Efficiency | Ratio of the extinction cross-section to the projected area of the particle (Ρr2 for a sphere) (Roberts 2007). |
| False Color Image | A color image where parts of the non-visible EM spectrum are expressed as one or more of the red, green, and blue components, so that the colors produced by the Earth's surface do not correspond to normal visual experience. Also called a false-color composite (FCC). The most commonly seen false-color images display the very-near infrared as red, red as green, and green as blue (sdc.ucsb.edu). |
| False Color Photograph | Another term for IR color photograph (sdc.ucsb.edu). |
| Feature | 1. Overall appearance (sdc.ucsb.edu). |
| 2. A set of measurable properties diagnostic of a class or material (sdc.ucsb.edu). | |
| 3. Referring to geometric or geomorphic entities, such as a hill, stream, on anything found on a natural or manmade surface (sdc.ucsb.edu). | |
| Field of view | The solid angle through which an instrument is sensitive to radiation (sdc.ucsb.edu). |
| Filtering | In analysis, the removal of certain spectral or spatial frequencies to highlight features in the remaining image (sdc.ucsb.edu). |
| FIRMS | Fire Information for Resource Management System |
| Focal Length | In cameras, the distance from the optical center of the lens to the plane at which the image of a very distant object is brought into focus (sdc.ucsb.edu). |
| Forb | Frequently used in vegetation ecology and especially in grasslands, forb refers to broad-leaved (dicot) herbs other than grasses. |
| Forced Convection | Convective mixing resulting from mechanical processes, such as wind (Roberts 2007). |
| Forward Scatterer | Object that preferentially reflects radiation in the direction opposite of incident radiation. Snow is a forward scatterer (Roberts 2007). |
| Free Convection | Convection produced by thermal instability in response to a temperature gradient (Roberts 2007). |
| Frequency (ν) | Number of wave oscillations per unit time (Roberts 2007). |
| Fresnel’s Equations | Equations that describe the reflection or transmission of energy interacting with a smooth surface with complex refractive index N (Roberts 2007). |
| Gain | Ratio of maximum quantization (QCALMAX) to the difference between minimum and maximum radiance measured by a detector when radiometrically calibrated in the laboratory Used to relate DNs to radiance (Roberts 2007). |
| GCP | Ground-control point: a geographic feature of known location that is recognizable on an image and can be used to determine geometrical corrections (sdc.ucsb.edu). |
| Geocoding | Geographic referencing or coding of the location of data items (sdc.ucsb.edu). |
| Geographic North | Same as true north. The direction from any point on the earth's surface toward the geographic North Pole; the northerly direction along any projection of the earth's axis upon the earth's surface, for example, along a longitude line. Except for much of navigational practice (which uses magnetic north), geographic north is the universal 0° (or 360°) mapping reference (amsglossary.allenpress.com). |
| Geometric Correction | Image-processing procedure that corrects spatial distortions in an image (sdc.ucsb.edu). |
| Geostationary Satellite | A satellite that orbits the earth at the same rate that the earth rotates and thus remains over a fixed place above the equator (Ahrens 2007). |
| GFS | Global Forecast System (a numerical weather forecast model) |
| GIS | Geographic Information Systems |
| GOES | Geostationary Operational Environmental Satellites |
| Goleta Foothills | One of several locations containing weather equipment that is designed to collect information on relative humidity, leaf wetness, and wind speed. The Goleta Foothills weather station is approximately 6.3 km from Coal Oil Point Reserve, 11.7 km from the Santa Ynez Mountain Peak, and 5.5 km from the KSBA weather station. |
| Gray Scale | A sequence of gray tones ranging from black to white (sdc.ucsb.edu). |
| Greenwich Mean Time | The world standard time that was implemented in Greenwich England and is based on the earth's motion (srrb.noaa.gov). |
| Greybody | Emitting object in which emissivity is below 1, but does not vary with wavelength (Roberts 2007). |
| Ground Receiving Station | Facility that records data transmitted by a satellite, such as Landsat (sdc.ucsb.edu). |
| Gymnosperm | Naked seeds not enclosed in an ovary that are produced by any group of vascular plants. Formerly considered a class (Gymnospermae) of seed plants, they are now considered polyphyletic in origin and divided into several extinct divisions and four divisions with surviving members typified by the cycadophytes, conifers, ginkgo, and ephedras. |
| Habitat | The explicit spatial, physical, and biological environment in which species can be found (MacDonald, 2003). |
| Heading | The direction toward which an aircraft or ocean vessel is oriented. A heading may be with reference to true north or magnetic north. The heading and course may be different, especially in air navigation, because of drift (amsglossary.allenpress.com). |
| Heat | A form of energy transferred between systems, existing only in the process of transfer. 2. Same as enthalpy (amsglossary.allenpress.com). |
| Hectopascal (hPa) | A hectopascal is equal to 100 pascals or 1 millibar (amsglossary.allenpress.com). Averaged over the entire planet, standard air pressure at sea level is 1013.25 hectopascals. Actual air pressure at sea level generally changes by only a few hectopascals per day, and is almost always between 880 and 1080 hectopascals. |
| Herb | A seed-producing annual, biennial, or perennial that dies down towards the end of a growing season since it does not develop persistent woody tissue. |
| High-pass filter | A spatial filter which selectively enhances contrast variations with high spatial frequencies in an image. It improves the sharpness of images and is a method of edge enhancement (sdc.ucsb.edu). |
| Hue | The attribute of colors that allows them to be classed as red, yellow, green, blue, or an intermediate between them; one of the terms that image interpreters commonly use to describe the color of objects in remotely sensed imagery (Jensen 2007). |
| Humidity | Humidity is a measure of the moisture content of air. Several types of humidity measures exist, including relative humidity, specific humidity, and dew point. |
| Hydrology | The scientific study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water on or below the land surface (weather.gov). |
| Hydrostatic Equilibrium | A fluid with surfaces of constant pressure and mass that is coincident and horizontal throughout. With hydrostatic equilibrium there exists a complete balance between the force of gravity and the pressure force (amsglossary.allenpress.com). |
| Hyperspectral | Remote sensing systems collecting data in hundreds of bands of the electromagnetic spectrum are generally called hyperspectral, while remote sensing systems that have over 1000 bands are generally called hyperspectral, and remote sensing systems that have a number of bands between 2 and 99 are generally called multispectral (Jensen 2007). |
| IHS | Intensity, hue, and saturation system of colors (sdc.ucsb.edu). |
| Image | Pictorial representation of a scene recorded by a remote sensing system. Although image is a general term, it is commonly restricted to representations acquired by non-photographic methods (sdc.ucsb.edu). |
| Image Enhancement | Any of a group of operations (e.g., contrast stretch, spatial filtering) that improve the detectability and presentation of targets or categories in an image (sdc.ucsb.edu). |
| Image Processing | Encompasses all the various operations that can be applied to producing the final photographic or computer-based image rendition (sdc.ucsb.edu). |
| Incidence Angle | In radar, the angle formed between an imaginary line normal to the surface and another connecting the antenna and the target (sdc.ucsb.edu). |
| Inclination | Orbital inclination is the angle between the orbital plane of an object and a reference plane that passes through the body being orbited. The inclination of a planetary orbit in the Solar System is measured from the ecliptic (the plane of Earth's orbit around the Sun). The inclination of an earth-orbiting satellite is the angle between the satellite's orbital plane and the plane that contains the earth's equator. Thus, an inclination of 0 degrees is a perfect equatorial orbit, and an inclination of 90 degrees is a perfect polar orbit, although satellites with inclinations of 80-90 degrees are generally considered polar-orbiting satellites (nasa.gov). |
| Index of Refraction (N) | The ratio of the free- space speed of light c, a universal constant, to the phase velocity of a plane harmonic electromagnetic wave in an optically homogeneous, unbounded medium (amsglossary.allenpress.com). It is the property of a material that describes the degree to which electromagnetic radiation changes velocity and is absorbed within the medium. Defined mathematically as N = n+ik where n is the simple refractive index (the ratio of the speed of light in a vacuum to the speed of light within the medium) and k is an extinction coefficient. k is multipled by an imaginary number (i = the square root of -1, i2 = 1, etc.) (Roberts 2007). |
| Infrared | Pertaining to EMR in the 0.7 to 100 µm region of the spectrum (sdc.ucsb.edu). |
| Infrared Satellite Imagery | This satellite imagery senses surface and cloud top temperatures by measuring the wavelength of electromagnetic radiation emitted from these objects. This energy is called "infrared". High clouds are very cold, so they appear white. Mid-level clouds are somewhat warmer, so they will be a light gray shade. Low cloud are warmer still, so they appear as a dark shade of gray or black. Often, low clouds are the same temperature as the surrounding terrain and cannot be distinguished at all. The satellite picks up this infrared energy between 10.5 and 12.6 micrometer (um) channels (weather.gov). |
| In Situ | Unlike remote sensing which collects data from a distance, in situ (or in-place) data collection occurs directly in the field (MacDonald, 2003). |
| Insolation | Insolation is the intensity of incoming solar radiation on an object (nsidc.org). |
| Intensity | The magnitude of brightness; one of the terms that image interpreters commonly use to describe the color of objects in remotely sensed imagery (Jensen 2007). |
| Interference | Interaction of two electromagnetic waves. If the waves are in phase (the peaks of one wave correspond to the peaks of the other wave), interference is constructive, increasing the amplitude (intensity) of the waves. If the waves are exactly out of phase (the peaks of one wave correspond to the troughs of the other wave), interference is destructive (Roberts 2007). |
| Irradiance (E) | Radiant flux arriving at a unit area integrated over all possible angles of incidence (θ) and azimuth (φ), generally expressed in units of Watts per square meter (W m-2). Also called radiant flux density (Roberts 2007). In general, irradiance depends on the orientation of the surface. The radiant energy may be confined to a narrow range of frequencies or wavelengths, in which case it would be called "spectral irradiance" or "monochromatic irradiance," or integrated over a broad range of frequencies or wavelengths, in which case it would be "all-wave irradiance" (amsglossary.allenpress.com). |
| Isobar | A line connecting points of equal pressure (Ahrens 2007). |
| Julian Date | The day of the year counting up from January 1st, which has a Julian date of 1, to December 31st, which has a Julian date of 365 (or 366 for leap years). Click here for a Julian Date Conversion Table (pdf). |
| Kelvin (K) | A unit of temperature that starts at absolute zero. Required for most radiation laws. Ice melts at 273.15 K (Roberts 2007). |
| Kinetic Energy | The ability of a moving body to do work by virtue of its motion. The molecular motion of matter is a form of kinetic energy (sdc.ucsb.edu). |
| Kinetic Temperature | Internal temperature of an object determined by random molecular motion. Kinetic temperature is measured with a contact thermometer (sdc.ucsb.edu). |
| Kirchhoff’s Law | Law that states total energy equals the sum of energy reflected, transmitted and absorbed by an object (1=ρ+T+α). For an optically thick (non-transmitting) object, absorption equals emissivity at a specific wavelength (Roberts 2007). |
| KSBA | The callsign for the automated surface observing system (ASOS) weather station at Santa Barbara Airport, California, located at approximately 34°25.55'N / 119°50.62'W. To save space on weather maps, and generally abbreviate things, the letter "K" at the beginning of callsigns will often be omitted, because many of these kinds of stations in the United States have callsigns beginning with the letter "K." |
| KVBX | The callsign used by the doppler radar station, and radiosonde launching station, at Vandenberg Air Force Base, California |
| Lambert’s Law | Law that states that radiance measured at an angle of incidence, θ, decreases as a function of the cosine of the angle of incidence: L(θ)=Lcos(θ). Also known as the cosine law (Roberts 2007). |
| Lambert Surface | A surface in which radiance is independent of viewing (exitance) angle, varying only as a function of the cosine of the angle of incidence (white paper is a good example) (Roberts 2007). |
| Langley Plot | Plot of the natural log of voltage (y) against airmasses (x). Used to calculate optical thickness as -1 times the slope of the line for a specific wavelength. The intercept of the plot can be used to determine the solar constant if the instrument is calibrated. |
| Latent Heat (LE) | Heat transfer due to a change in phase of a liquid, solid or vapor (for example, vaporization, melting or condensation) (Wm-2) (Roberts 2007). |
| Latent Heat of Fusion | Heat released or absorbed during the process of freezing or melting (3.35 x105 J kg-1) (Roberts 2007). |
| Latent Heat of vaporization | Heat released or absorbed during the process of condensation or vaporization (2.468 x106 J kg-1) (Roberts 2007). |
| Latitude (β) | Angular distance north or south of the equator. By convention, north is positive, south is negative (Roberts 2007). |
| Leaf Wetness Sensor | A leaf wetness sensor generally detects water and ice on the sensor's surface by measuring the dielectric constant of the upper surface. |
| Longitude (λ) | Angular distance east or west of the prime meridian (Greenwich, England). By convention, angles are negative west of the prime meridian (Roberts 2007). |
| Longwave Radiation | Radiation with long wavelengths (generally around 2.5 to 14μm) , typically corresponding to the part of the spectrum dominated by radiation emitted by the Earth's surface and atmosphere (Roberts 2007). |
| Look Angle | The angle between the vertical plane containing a radar antenna and the direction of radar propagation. Complementary to the depression angle (sdc.ucsb.edu). |
| LST | Local standard time is the offical time observed in the local time zone when not on daylight savings (LDT is local daylight time, and is generally one hour ahead of LST). |
| Magnetic North | At any point on the earth's surface, the horizontal direction of the earth's magnetic lines of force (direction of a magnetic meridian) toward the north magnetic pole, that is, a direction indicated by the needle of a magnetic compass (amsglossary.allenpress.com). |
| Meridional | In meteorology, a flow, average, or functional variation taken in a direction that is parallel to a line of longitude; along a meridian; northerly or southerly; as opposed to zonal (amsglossary.allenpress.com). |
| Mesosphere | The atmospheric layer between the stratosphere and the thermosphere. Located at an average elevation between 50 and 80 km above the earth's surface (Ahrens 2007). |
| METAR | Meteorological Routine Weather Report (typically meaning a weather measurement made at airports once per hour) |
| Meteorology | The study of the atmosphere and atmospheric phenomena as well as the atmosphere's interaction with the earth's surface, oceans, and life in general (Ahrens 2007). |
| Micrometer (μm) | (Also called micron; abbreviated μm.) A unit of length equal to one millionth of a meter or one thousandth of a millimeter. The micrometer is a convenient length for measuring wavelengths of infrared radiation, diameters of atmospheric particles, etc. (amsglossary.allenpress.com). |
| Mie Scattering | Scattering process in which the particle dimensions are approximately proportional to the wavelength of light. Usually caused by small particles, such as dust, pollen, or bacteria (Roberts 2007). |
| Millibar (mb) | A unit for expressing atmospheric pressure. Sea-level pressure is normally close to 1013 mb (Ahrens 2007). |
| MODIS | Moderate Resolution Imaging Spectroradiometer |
| MOS | Model Output Statistics MOS products adjust numerical weather forecast model outputs for specific locations, based upon statistical relationships between model performance in similar situations in the past with the actual weather observed at those locations. Thus, MOS attempts to account for situations in which numerical models habitually over- or under-predict weather variables (such as rainfall amounts) for certain locations, which happens often. Operational weather forecasters often use MOS to guide their decisions about what to put in their forecasts. |
| Mottled | Having blotches or spots; one of the terms that image interpreters commonly use to describe the textures of objects in remotely sensed imagery (Jensen 2007). |
| MRF | Medium Range Forecast Model |
| Multispectral | Multispectral remote sensing systems record emitted or reflected energy that comes from an object or specific area of interest in multiple bands of the electromagnetic spectrum. Remote sensing systems that are capable of recording hundreds of bands of the electromagnetic spectrum are generally called hyperspectral, while remote sensing systems collecting data in thousands of bands are generally called ultraspectral (Jensen 2007). |
| Nadir | 1. Satellite subpoint on the earth's surface that is centered directly below the satellite (amsglossary.allenpress.com). |
| 2. The point on a given observer's celestial sphere diametrically opposite his zenith, that is, directly below the observer (amsglossary.allenpress.com). | |
| NAM | North American Model (a numerical weather forecast model) |
| Nanometer (nm) | One billionth of a meter. The visible part of the electromagnetic spectrum, to which most human eyes are responsive, is generally approximated as being between the wavelengths of 400 to 700 nanometers. |
| NAPP | National Aerial Photography Program |
| NASA | National Aeronautics and Space Administration |
| Natural Color | Same as true color. Generally used to describe remote-sensing images displayed with a band combination producing the same colors that human observers with normal vision would see if they were there in person. This typically means that a band around 650 nm is displayed as red, a band around 550 nm is displayed as green, and a band around 450 nm is displayed as blue. Most photographs from consumer-grade cameras (film or digital) are natural-color images. |
| NCAR | National Center for Atmospheric Research |
| NCEP | National Centers for Environmental Prediction |
| NESDIS | National Environmental Satellite, Data, and Information Service |
| Net Radiation | Sum of incoming and outgoing short-wave and long-wave radiation (Roberts 2007). |
| Net Radiometer | Net Radiometers measure the energy balance between incoming short-wave and long-wave IR radiation in relation to reflected short-wave and outgoing long-wave IR radiation. |
| NGM | Nested Grid Model (a numerical weather forecast model) |
| NOAA | National Oceanic and Atmospheric Administration |
| Non-Selective Scattering | Scattering process in which the particle dimensions are much larger than the wavelength of light, such as water droplets. Results in no preferential scattering as a function of wavelength. White clouds are an example (Roberts 2007). |
| NORAD | North American Aerospace Defense Command |
| NRL | Naval Research Laboratory |
| Numerical weather forecast model | Weather forecasters base much of their decisions on output from these computer models, which use data from weather stations, radiosondes, and other sources, along with the laws of physics and parameterizations of atmospheric processes, to simulate upcoming weather. Predictive skill decreases dramatically for forecasts of the weather more than a few days in advance. |
| NWS | National Weather Service |
| Offset | Radiance measured at a DN value of 0 (Roberts 2007). |
| Old Growth Forest | Forest that has not experienced large disturbances or human land clearance for hundreds of years (MacDonald, 2003). |
| Optical Thickness (τ) | Extinction coefficient integrated over the physical thickness of the medium. For the atmosphere, this equals the total atmospheric column perpendicular to the surface. Normal optical thickness is the sum of the optical thicknesses of all absorbing or scattering components (Roberts 2007). |
| Orbital Inclination | Orbital inclination is the angle between the orbital plane of an object and a reference plane that passes through the body being orbited. The inclination of a planetary orbit in the Solar System is measured from the ecliptic (the plane of Earth's orbit around the Sun). The inclination of an earth-orbiting satellite is the angle between the satellite's orbital plane and the plane that contains the earth's equator. Thus, an inclination of 0 degrees is a perfect equatorial orbit, and an inclination of 90 degrees is a perfect polar orbit, although satellites with inclinations of 80-90 degrees are generally considered polar-orbiting satellites (nasa.gov). |
| Orthoimage | Typically aerial images that are geometrically corrected to have constant scale throughout each image and no terrain displacement: they look how the ground would hypothetically appear from the perspective of being directly above every point on the surface (Jensen 2007). |
| Parameterization | Mathematical treatment to simplify certain physical processes in numerical models; for example, most numerical models use parameterizations to approximate convection and precipitation processes because modeling them fully would be extremely computationally intensive or even impossible at the spatiotemporal resolutions of some models. |
| Particulates | Small particles such as fine dust, soot from combustion, salt particles etc. Can be called aerosols (Roberts 2007). |
| Path Radiance | Diffuse upwelling radiation that is a product of scattered direct beam and scattered reflected solar radiation. Must be removed from measured upwelling radiance to calculated radiance reflected at the surface (Roberts 2007). |
| Path Transmittance | Measure of degree of attenuation of upwelling surface radiance (Roberts 2007). |
| Pattern | Spatial arrangement of objects on the ground; one of the terms that image interpreters commonly use to describe the order of objects in remotely sensed imagery (Jensen 2007). |
| PDT | Pacific Daylight Time, which is the time zone that contains UCSB. PDT is always 7 hours behind UTC time, but most areas in the Pacific Time Zone of the United States, including UCSB, aren't on PDT for the entire year: they generally use Pacific Daylight Time (PDT) only from the second Sunday in March to the first Sunday in November. For the rest of the year, these places are on Pacific Standard Time (PST). See timeanddate.com for current times in various time zones and steps for conversions between time zones. |
| Perennial | A plant that lives for several growing seasons; compare to "annual" (MacDonald, 2003). |
| Permafrost | A layer of soil or bedrock at a variable depth beneath the surface of the earth in which the temperature has been below freezing continuously from a few to several thousands of years (amsglossary.allenpress.com). |
| phAR | Photosynthetically active radiation. This normally corresponds to visible light (MacDonald, 2003). |
| Phenology | Changes in the growth and reproduction of plants and animals brought about by seasonal timing (MacDonald 2003). |
| Photoperiodism | The influence of seasonal or daily changes in light intensity on organisms (MacDonald, 2003). |
| Photorespiration | The release of carbon dioxide by plants without photosynthetic production having occurred (MacDonald, 2003). |
| Photosynthesis | The process by which plants combine water and carbon dioxide in the presence of sunlight to capture visible light spectrum electromagnetic energy in the sunlight and transform it into chemical energy in the form of simple sugars (MacDonald, 2003). |
| Pitch | The oscillation of a ship about the lateral axis, that is, alternate rising and falling of bow and stern. All the motions of a ship or aircraft can be regarded as combinations of oscillations about three different axes, and these motions are called roll, pitch, and yaw (amsglossary.allenpress.com). From the perspective of a pilot who is looking forward (towards the direction in which the aircraft is traveling), a change in pitch would mean the aircraft is moving up or down but keeping the same heading. Also see "roll" and "yaw." |
| Pixel | A picture element, that is, a single element of an image or picture. A pixel is the smallest element of a picture. Other elements are rows, columns, and subframes, which are rectangular regions of the image or picture (amsglossary.allenpress.com). |
| Planck Equation | Equation that describes the intensity of electromagnetic radiation emitted by an object at a given temperature at a specific wavelength (Roberts 2007). |
| Plankton | Organisms that exist by passively floating in the waters of an ocean, lake, or other water body. These include many microscopic plants (phytoplankton) and small invertebrate animals (zooplankton) (MacDonald, 2003). |
| Polarization | Oscillation of the electric field in a preferred plane. In optical wavelengths parallel (horizontal) polarized radiation oscillates in a plane that is perpendicular to a horizontal surface and perpendicular (vertical) radiation oscillates in a plane that is parallel to a horizontal surface (Roberts 2007). |
| Polar orbiting satellite | A satellite whose orbit closely parallels the earth's meridian lines and thus crosses the polar regions on each orbit (Ahrens 2007). |
| Potential Temperature (θ) | Temperature of an air parcel cooled or heated adiabatically to 1000 mb pressure level (Roberts 2007). |
| Precipitable water | The total atmospheric water vapor contained in a vertical column of unit cross-sectional area extending between any two specified levels, commonly expressed in terms of the height to which that water substance would stand if completely condensed and collected in a vessel of the same unit cross section (amsglossary.allenpress.com). |
| Precipitation | Precipitation is any form of water particle, whether it be solid or liquid, that falls from the atmosphere and lands on the ground (nsidc.org). |
| Primary Forest | Forest which has not experienced significant human modification of land clearance (MacDonald, 2003). |
| Prime Meridian | Defined as 0 degrees longitude, it is an imaginary line that runs from the north pole to the south pole. It is the point for which UTC is defined (srrb.noaa.gov). |
| Principal Point | The point on the earth where a satellite sensor is focused at any time during its orbit (amsglossary.allenpress.com). |
| Projection | The correspondence between a domain of the earth's surface and a plane surface (map) such that each point on one corresponds to one and only one point on the other. Typical projections used on weather charts include stereographic, Lambert conic, and Mercator (amsglossary.allenpress.com). |
| PST | Pacific Standard Time, which is the time zone that contains UCSB. PST is always 8 hours behind UTC time, but most areas in the Pacific Time Zone of the United States, including UCSB, aren't on PST for the entire year: they generally use Pacific Daylight Time (PDT) from the second Sunday in March to the first Sunday in November. See timeanddate.com for current times in various time zones and steps for conversions between time zones. |
| Pyranometer | The LI200X Silicon Pyranometer is used to accurately measure sun plus sky radiation in the 400 to 1100 nm waveband. It is used extensivly in solar, agricultural, and meteorological applications. |
| Quantization | In remote sensing, this is the process in which voltage, as measured by a detector, is converted in to a digital number (DN) (Roberts 2007). |
| Radar | An electronic instrument used to detect objects (such as falling precipitation) by their ability to reflect and scatter microwaves back to a receiver (Ahrens 2007). |
| Radiance (L) | Radiant flux density measured over a specified range of incidence and azimuth angles (Ω: solid angle). Radiance generally has units of W m-2 sr-1, or W m-2 μm-1 sr-1 for spectral radiance, which is the most common form of measurement made by an optical remote sensor (Roberts 2007). |
| Radiant Energy (Q) | Measure of the capacity of electromagnetic energy to do work (Joules: kg m2 s-2) (Roberts 2007). |
| Radiant Flux (φ) | Rate at which radiant energy passes a point per unit time (Watts: Js-1) (Roberts 2007). |
| Radiant Temperature (Tr) | Apparent temperature of an object integrated across all wavelengths as described by the Stefan-Boltzmann equation (K). Radiant temperature equals kinetic temperature for a black body (Roberts 2007). |
| Radiation | Usually refers to "electromagnetic radiation," which is a form of energy that moves at the speed of light and is made of photons, which are tiny particles of energy that have wave-like properties such as wavelength, period, and frequency. |
| Radiation Budget | -Measurement of daily incoming solar radiation headed towards Earth's surface and the outgoing radiation that leaves the Earth's sruface at night (srrb.noaa.gov). -Also defined as an accounting of radiant energy that is lost or gained by the atmosphere for a given place and time (amsglossary.allenpress.com). |
| Radiometric Calibration | Process in which encoded radiance, measured at a detector, is converted to photons or radiance (Roberts 2007). |
| Radiosonde | A weather balloon that transmits data on atmospheric temperature, pressure, and humidity at heights above the surface, usually all the way through the troposphere and into the lower stratosphere. A rawinsonde is basically the same thing, but also provides wind data (weather.gov). |
| Rain gage | An instrument that measures amounts of liquid precipitation, which is indeed generally spelled "gage," not "gauge." These are often "tipping bucket" rain gages, which funnel precipitation into a bucket that tips when the calibrated level is reached (generally this calibrated level is small, such that each tip represents a fraction of a centimeter of rain). As the bucket tips, a magnet attached to the tipping mechanism flips a switch, sending information to a data logger. |
| Range | The geographic area permanently occupied by a plant or animal taxon (MacDonald, 2003). |
| RAWS | Remote Automated Weather Stations Typically refers to the network managed by the United States Forest Service and other government agencies. |
| Rayleigh Scattering | Scattering process in which scattering is inversely proportional to 1/λ4. Caused by particles that are much smaller than the wavelength of light. Also known as molecular scattering. The process that produces blue skies (Roberts 2007). |
| Reciprocity Principle | Law that states that the BRDF remains the same if the reflection and illumination angles are interchanged (Roberts 2007). |
| Rectify | |
| Reflectance (ρ) | Ratio of energy reflected by a material to total incident radiation. Represents a measured quantity (Roberts 2007). |
| Reflectivity (ρ) | Same as reflectance. Represents an intrinsic property of a material (Roberts 2007). |
| Register | The writing component of a recording instrument. It is frequently located at some distance from the sensing portion of the instrument (amsglossary.allenpress.com). |
| Registration | Process of superposing two or more images or photographs so that equivalent geographic points coincide (sdc.ucsb.edu). |
| Relative Humidity | The ratio of the amount of water vapor in the air compared to the amount required for saturation (at a particular temperature and presssure). The ratio of the air's actual vapor pressure to its saturation vapor pressure (Ahrens 2007). |
| Regolith | Weathered rock and mineral matter from which soil is developed (MacDonald, 2003). |
| Remote Sensing | A method of obtaining information about properties of an object without coming into physical contact with that object (amsglossary.allenpress.com). |
| Restoration Ecology | The application of ecological principles and techniques to restore ecosystems that have been damaged by human activity (MacDonald, 2007). |
| Riparian | The environment along rivers and streams (MacDonald, 2003). |
| Roll | Oscillation of a ship or aircraft about the longitudinal axis. All the motions of a ship or aircraft can be regarded as combinations of oscillations about three different axes, and these motions are called roll, pitch, and yaw (amsglossary.allenpress.com). From the perspective of a pilot who is looking forward (towards the direction in which the aircraft is traveling), a change in roll would mean the aircraft is banking to the left or the right but keeping the same heading. Also see "yaw" and "pitch." |
| RUC | Rapid Update Cycle (a numerical weather forecast model) |
| Santa Ana wind | A warm, dry wind that blows into southern California from the east off the elevated desert plateau. Its warmth is derived from compressional heating (Ahrens 2007). |
| Saturation | 1. In meteorology, saturation is the condition in which vapor pressure is equal to the equilibrium vapor pressure over a plane surface of pure liquid water, or sometimes ice (amsglossary.allenpress.com). |
| 2. In remote sensing, saturation is the maximum radiance a detector can measure (the detector is generally not damaged when it saturates, but it also cannot distinguish among differences in radiance above this value). In other words, if a band saturates at, say, a radiance of 1.94 W m-2 μm-1 sr-1 (which is the case for MODIS's band 22 according to Salomonson et al. 2000), it cannot tell the difference between 2 W m-2 μm-1 sr-1 and 20 W m-2 μm-1 sr-1 (it would record both of them as having a radiance of 1.94 W m-2 μm-1 sr-1 in this band). | |
| 3. In remote sensing, saturation can also mean the degree of difference from the gray containing the same lightness; saturation is one of the terms that image interpreters commonly use to describe the color of objects in remotely sensed imagery (Jensen 2007). | |
| Saturation-adiabatic Lapse Rate | The rate of decrease of temperature with height along a moist adiabat (amsglossary.allenpress.com). |
| Saturation Vapor Pressure (SVP) | Vapor pressure exerted by air at saturation (Pa, mb) (Roberts 2007). |
| Scale Height (H) | Height at which molecular density, pressure or transmission are attenuated to 1/e. Scale height is determined from the hydrostatic equation and has a value of 8.434 km for molecular density and pressure. Aerosols and attenuation by water vapor have a different (smaller) value (Roberts 2007). |
| Second Growth Forest | The forest vegetation that initially develops following a large disturbance or human land clearance (MacDonald, 2003). |
| Sedgwick Reserve | Sedgwick Reserve (clicking link will open a PDF) One of several locations containing weather equipment that is designed to collect information on relative humidity, leaf wetness, and wind speed. The 5,896-acre reserve is located in the Santa Ynez Valley and is surrounded by hillsides that reach elevations as high as 2,300 feet. |
| Senescence | The aging process in mature individuals. In deciduous plants, it is the process that occurs before the shedding of leaves. Senescence can also refer to the period near the end of an organism's life cycle (perseus.tufts.edu). |
| Sensible Heat (H) | Heat exchange due to molecular movement in response to a temperature gradient (Wm-2) (Roberts 2007). |
| Shadow | Asilhouette caused by solar illumination from the side; one of the terms that image interpreters commonly use to describe objects in remotely sensed imagery (Jensen 2007). |
| Shortwave radiation | Radiation with short wavelengths (typically around 0.4 to 2.5μm), usually referring to the part of the electromagnetic spectrum dominated by incoming solar radiation (Roberts 2007). |
| Sidereal | Relating to stars or constellations |
| Silver halide | Silver halide crystals react to light, and are thus used for many kinds of films (Jensen 2007). |
| Simple refractive index (n) | Ratio of the speed of light in a vacuum to the speed of light in a medium. Equal to 1 or more (Roberts 2007). |
| Single scattering albedo (ω) | Ratio of scattered radiation (reflected and transmitted) to incident range. Milk would have a ω of 1, ink 0 (Roberts 2007). |
| Site | Elevation, slope, aspect, exposure, adjacency to water, transportation, utilities; one of the terms that image interpreters commonly use to describe objects in remotely sensed imagery (Jensen 2007). |
| Situation | Objects placed in a particular order or orientation relative to one another; one of the terms that image interpreters commonly use to describe the arrangement of objects in remotely sensed imagery (Jensen 2007). |
| Snell’s Law | The mathematical relation between angles of incidence and refraction at an interface between media with different refractive indices (Roberts 2007). |
| Soil | The uppermost layer of mineral and organic matter found on the earth's surface (MacDonald, 2003). |
| Soil Temperature | Soil temperature is the temperature measured at a given soil depth (amsglossary.allenpress.com). |
| Soil water balance | Soil Water Balance is the calculation of how much rain or irrigation water in a given soil depth is used by plants, or is lost through drainage or by surface runoff. (niwascience.co.nz). |
| Solar Declination | The declination of the sun. Solar Declination can vary from -23.44 degrees at the northern hemisphere winter solstice, through 0 degrees at the vernal equinox, to 24.44 degress at the summer solstice. Solar Declination is an astronomical description of the sun's variation in going south for winter (srrb.noaa.gov). |
| Solar Noon | Usually refers to local solar noon, the time of day at which the sun is at its highest point in the sky, which almost never coincides with 12pm local time, due to daylight savings, the arbitrary shapes of time zones, and the equation of time. |
| Solar zenith angle | Angle measured at the earth's surface between the sun and the zenith (amsglossary.allenpress.com). |
| Solstice | Either of the two points on the sun's apparent annual path where it is displaced farthest, north or south, from the earth's equator, that is, a point of greatest deviation of the ecliptic from the celestial equator (amsglossary.allenpress.com). |
| Spatiotemporal | Combining the time and space dimensions; spatiotemporal is a word that geographers like to use frequently. |
| Specific Heat (C) | The amount of heat (J) required to raise the temperature of a unit mass (kg) 1 Kelvin (Jkg-1K-1) (Roberts 2007). |
| Specific Humidity | The ratio of the mass of water vapor in a given air parcel to the total mass of air in the parcel (Ahrens 2007). |
| Spectral Response Function | Function that describes the manner in which energy measured by a sensor is weighted across a range of wavelengths (frequency etc.) (Roberts 2007). |
| Spectroradiometer | Remote sensing device that measures radiance at several different wavelengths. |
| Specular reflector | Mirror reflector. Still water behaves like a specular reflector (Roberts 2007). |
| Speed of Light (c) | Speed at which electromagnetic radiation travels in a vacuum (m s-1) (Roberts 2007). |
| Stand | A single plot of plants which particularly includes forest trees (MacDonald 2003). |
| Stereo base | Distance between a pair of correlative points on a stereo pair that are oriented for stereo viewing (sdc.ucsb.edu). |
| Stereo pair | Two overlapping images or photographs that may be viewed stereoscopically (sdc.ucsb.edu). |
| Stereoscopic | Two pictures taken with a spatial or time separation that are then arranged to be viewed simultaneously. When so viewed they provide the sense of a three-dimensional scene using the innate capability of the human visual system to detect three dimensions (amsglossary.allenpress.com). |
| Stippled | Small, short, dark spots that when applyed together produce even or softly graded shades or tones; one of the terms that image interpreters commonly use to describe the textures of objects in remotely sensed imagery (Jensen 2007). |
| Stratosphere | The layer of the atmosphere above the troposphere and below the mesosphere (between 10 km and 50 km), generally characterized by an increase in temperature with height (Ahrens 2007). |
| Subsolar Point | The point on a planet where its sun is perceived to be directly overhead. |
| Summer Solstice | For either hemisphere, the solstice at which the sun is above that hemisphere. In northern latitudes, this occurs approximately on 21 June (amsglossary.allenpress.com). |
| Superadiabatic Lapse Rate | An environmental lapse rate that exceeds the dry-adiabatic lapse rate. Potential temperature decreases with height as a result of this lapse rate. |
| Surface Fire | A fire that is restricted to the ground level and lower vegetation and does not rise into the tree canopy if trees are present (MacDonald, 2003). |
| Synodic | Synodic relates to the conjunction of celestial bodies, and often includes the interval between two successive conjunctions of a planet or the moon with the sun. |
| Synoptic Scale | The spatial scale of the migratory high and low pressure systems of the lower troposphere, with wavelengths of around 1000 to 2500 km (weather.gov). |
| Temperate | Having a geographic distribution in the temperate mid-latitude regions of the world (MacDonald, 2003). |
| Temperature | The quantity measured by a thermometer. Bodies in thermal equilibrium with each other have the same temperature. In gaseous fluid dynamics, temperature represents molecular kinetic energy, which is then consistent with the equation of state and with definitions of pressure as the average force of molecular impacts and density as the total mass of molecules in a volume. For an ideal gas, temperature is the ratio of internal energy to the specific heat capacity at constant volume (amsglossary.allenpress.com). |
| Texture | In a remotely-sensed image, the frequency of change and arrangement of tones, often due to highlights and shadows created by the irregular surface being viewed (amsglossary.allenpress.com). Terms that image interpreters commonly use to describe the textures of objects in remotely sensed imagery include: smooth, intermediate (medium), rough (coarse), mottled, and stippled (Jensen 2007). |
| Thermal Conductivity (K) | Material property that controls the magnitude of heat flow in response to a thermal gradient (W m-1 K-1) (Roberts 2007). |
| Thermal Diffusivity (α) | Ratio of thermal conductivity to volumetric heat capacity. A measure of the rate of change in temperature per unit time (m2 s-1) (Roberts 2007). |
| Tone | Each distinguishable shade of gray from white to black on an image (sdc.ucsb.edu). |
| Topography | The shape of the land (weather.gov). |
| Transmissivity (T) | Same as transmittance. Represents an intrinsic property of a material (Roberts 2007). |
| Transmittance (T) | Ratio of energy transmitted by a material to total incident radiation. Represents a measured quantity (Roberts 2007). |
| Transpiration | The release of water vapor to the air by plants (MacDonald, 2003). |
| Tropopause | The boundary between the troposphere and the stratosphere (Ahrens 2007). |
| Troposphere | The layer of the atmosphere extending from the earth's surface up to the tropopause (about 10 km above the ground) (Ahrens 2007). |
| True-color | Same as natural color. Generally used to describe remote-sensing images displayed with a band combination producing the same colors that human observers with normal vision would see if they were there in person. This typically means that a band around 650 nm is displayed as red, a band around 550 nm is displayed as green, and a band around 450 nm is displayed as blue. Most photographs from consumer-grade cameras (film or digital) are true-color images. |
| True North | The direction from any point on the earth's surface toward the geographic North Pole; the northerly direction along any projection of the earth's axis upon the earth's surface, for example, along a longitude line. Except for much of navigational practice (which uses magnetic north), true north is the universal 0° (or 360°) mapping reference (amsglossary.allenpress.com). |
| UCSB | University of California, Santa Barbara |
| Ultraspectral | Remote sensing systems collecting data in thousands of bands of the electromagnetic spectrum are generally called ultraspectral, while remote sensing systems that have a number of bands between 100 and 999 are generally called hyperspectral, and remote sensing systems that have a number of bands between 2 and 99 are generally called multispectral (Jensen 2007). |
| Ultraviolet | Region of the electromagnetic spectrum that falls outside of the visible portion and just beyond the violet. It is between 200 and 390 nanometers in wavelength of the spectrum (srrb.noaa.gov). |
| USDA | United States Department of Agriculture |
| USGS | United States Geological Survey |
| UTC | UTC is an international compromise for the acronym to be used for "coordinated universal time," which is basically the time zone that contains Greenwich, England, although UTC is never on daylight savings. UTC is also known as "Greenwich Mean Time" (GMT), "Z time" and "Zulu time" (amsglossary.allenpress.com). In other words, "09:30 Z" (which most professionals would pronounce "zero-nine-thirty Zulu") means 09:30 UTC. Each time zone is officially assigned a letter of the alphabet, and "Z" is given to UTC. See timeanddate.com for current times in various time zones and steps for conversions between time zones. |
| Vapor Pressure | The pressure exerted by the water vapor molecules in a given volume of air (Ahrens 2007). |
| Variation | Magnetic variation (also called magnetic declination) is the angle between true north and magnetic north, which varies with geographic location (amsglossary.allenpress.com). If you know the magnetic declination for your area, you can use this to determine true north using a magnetic compass. For example, UCSB's geographic location gives it a magnetic declination of about 14 degrees east (so from the perspective of someone on the ground near UCSB, the magnetic north pole is about 14 degrees east of the geographic north pole). Thus, to get true headings (such as true north) for measurements made near UCSB, subtract 14 degrees from the headings read from a magnetic compass. Some compasses allow the user to align the pointer to be a certain angle away from the direction their magnetic needle is pointing, and setting that angle to the magnetic declination for the area will make headings read off the compass to be true headings, instead of magnetic headings. |
| Visible Light | Region of the electromagnetic spectrum that can be seen by the human eye. Visible light falls within wavelengths 390-780 nm of the electromagnetic spectrum and it includes the colors violet, indigo, blue, green, yellow, orange, and red (srrb.noaa.gov). |
| Volumetric Heat Capacity (Cp) | The amount of heat (J) required to raise the temperature of a unit volume (m3) 1 Kelvin (Jm-3K-1) (Roberts 2007). |
| Water Vapor | Water in a vapor (gaseous) form. Also called moisture (Ahrens 2007). |
| Wavelength (λ) | Distance measured in the direction of wave propagation between two points at the same phase (nm, μm, cm, m) (Roberts 2007). |
| Wavenumber (η) | A measure of frequency calculated as 1 divided by distance in cm (1/cm) (Roberts 2007). |
| Weathering | The physical, chemical, and biological processes that cause rocks to break down into fine particles and soluble chemicals (MacDonald, 2003). |
| Wet-bulb Temperature | The temperature an air parcel would have if it cooled adiabatically to saturation at constant pressure by evaporation of water into it (amsglossary.allenpress.com). |
| Wien’s Displacement Law | Law that defines the wavelength at which maximum energy is emitted by an object of a given temperature. Wien’s constant = 2897.79 K (Roberts 2007). |
| Wind | Wind is made of air that is in motion relative to the Earth's surface. Wind speed is the ratio of a unit distance covered by the air to the time taken to cover it. Winds are typically named for the direction from which the wind is blowing (so a wind coming from the west would be a "westerly" wind, and a sea breeze would be wind blowing from the sea towards the land). Exceptions to this rule include "onshore" breezes, which are winds blowing onto the shore (from the water) and "offshore" breezes, which blow from the shore towards the water. |
| Wind Vane | An instrument used to indicate or measure wind direction (Ahrens 2007). |
| Winter Solstice | For either hemisphere, the solstice at which the sun is above the opposite hemisphere. In northern latitudes, the time of this occurrence is approximately 22 December (amsglossary.allenpress.com). |
| WWLLN | World-Wide Lightning Location Network |
| Xerophyte | Plants that require dry soils (MacDonald, 2003). |
| Yaw | Oscillation of a ship or aircraft about the vertical axis. All the motions of a ship or aircraft can be regarded as combinations of oscillations about three different axes, and these motions are called roll, pitch, and yaw (amsglossary.allenpress.com). From the perspective of a pilot who is looking forward (towards the direction in which the aircraft is traveling), a change in yaw would mean the aircraft is turning to the left or the right but keeping the same orientation with respect to the horizon. Also see "roll" and "pitch." |
| Youg | A hot wind during unsettled summer weather in the Mediterranean (amsglossary.allenpress.com). |
| Young Ice | Newly formed, flat sea or lake ice, usually between 2 and 8 in. thick. Further growth renders it winter ice (amsglossary.allenpress.com). |
| Z Time | Also called "Zulu time," this is the same as coordinated universal time (UTC) (amsglossary.allenpress.com). In other words, "15:00 Z" (which most professionals would pronounce "fifteen-hundred Zulu") means 15:00 UTC. Each time zone is officially assigned a letter of the alphabet, and "Z" is given to UTC. Zulu time and UTC are never on daylight savings. |
| Zenith | That point, on any given observer's celestial sphere, that lies directly above him; the point that is elevated 90° from all points on a given observer's astronomical horizon. Diametrically opposite the zenith is the observer's nadir (amsglossary.allenpress.com). |
| Zenith Distance | The angular distance of any celestial object from a given observer's zenith, measured along the great circle of the celestial sphere from the zenith to the object; the complement of the elevation angle (amsglossary.allenpress.com). |
| zero-plane displacement | A height scale in turbulent flow over tall roughness elements associated with the average level of action of momentum transfer between the flow and the roughness elements (amsglossary.allenpress.com). |
| Zonal | In meteorology, latitudinal, that is, easterly or westerly; opposed to meridional (amsglossary.allenpress.com). |