Glossary of Terms and Acronyms - A - C

ABSOLUTE HUMIDITY

The total amount (mass) of water vapor per unit volume of air. Measured in units of gram per kilogram (g/kg).

ABSORPTION

A measure of the amount of solar energy absorbed by a given substance of definite dimensions; the ratio of the amount of radiant energy absorbed to the total amount incident upon that substance.

ACCELEROMETER

Device measuring changes in velocity in x,y, and z directions with respect to the aircraft.

ACES

Altus Cumulus Electrification Study (ACES) was based at the Naval Air Facility Key West in Florida, ACES researchers in August 2002 chased down thunderstorms using an uninhabited aerial vehicle (UAV) - allowing them to achieve dual goals of gathering weather data safely and testing new aircraft technology. This marked the first time a UAV was used to conduct lightning research. Aimed at better understanding the causes of an electrical storm's fury and its effects on our home planet, this study was a collaboration among the Marshall Center; the University of Alabama at Huntsville; NASA's Goddard Space Flight Center, Greenbelt, Md.; Pennsylvania State University, University Park; and General Atomics Aeronautical Systems Inc., San Diego.

ADVANCED MICROWAVE SOUNDING UNIT-B (AMSU-B)

AMSU-B is a 5 channel microwave radiometer (89.0, 150.0, and 3 at 183.31Ghz) whose purpose is to receive and measure radiation from a number of different layers of the atmosphere in order to obtain humidity profiles.

AERI

Atmospheric Emitted Radinace Interferometer, a passive Michelson interfometer observing in the near infrared portions of the spectrum which is used to remotedly obtain temperatuere and water vapor retrievals.

AEROSOL BACKSCATTER

Electromagnetic radiation from small atmospheric constitiuents which is retro-reflected or emitted back to the source/the measuring device.

AEROSOL EXTINCTION

The vertical profile produced based on the backscatter of certain wavelengths that are highly attenuated by aerosols and clouds.

AEROSOL OPTICAL DEPTH/THICKNESS

The degree to which aerosols prevent light from passing through. Optical depth/thickness depends upon the physical constitution, the form and the concentration of particles.

AEROSOL PARTICLE PROPERTIES

Adjectives describing the characteristics of Aerosol Particles, e.g. composition, size, diameter.

AEROSOL/CLOUD PARTICLE SIZER

The APS provides high-resolution, real-time aerodynamic measurements of particles from 0.5 to 20 micrometers, providing number-weighted, particle size distributions.

AEROSONDE

The Aerosonde is an unmanned aerial vehicle with a wingspan of a 2.9 meters (~9 feet) weighing approximately 14 Kg (~31 lbs). Carrying a payload of air pressure, temperature and humidity probes.

AETHAELOMETER

The aethaelometer is an instrument that measures suspended carbonaceous particulates, an important species of air pollutant.

AIR MOTION SENSOR

The Air Motion Sensor is a system comprised of the Pitot-Static System and Total Temperature Probe which determines the motion of the air with respect to the aircraft.

AIR TEMPERATURE

A measure of the average kinetic energy of air molecules.

AIRCRAFT

Any weight-bearing vehicle designed for navigation in and through the air, supported by the action of air upon its surfaces or by the vehicle's own buoyancy

AIRCRAFT MOTION SENSOR

An aircraft motion sensor is comprised of the GPS and INS plus associated hardware. Used to determine the motion of the aircraft with respect to the surface of the earth.

AIRSPEED/GROUND SPEED

Airspeed is the velocity of a vehicle through the atmosphere. Groundspeed is the velocity of a vehicle measured with respect to the ground.

ALTUS

ALTUS is an Unmanned Aerial Vehicle (UAV) that is used to carry instruments for remote and direct sensing of atmospheric phenomena.

ALTUS DATA COLLECTION SYSTEM

A system used to collect data and events, such as flight and vehicle parametersfrom the Altus Unmanned Aerial Vehicle (UAV).

AMPR

The Advanced Microwave Precipitation Radiometer is a passive microwave radiometer system on an airborne platform that collects data at 10.7 GHz, 19.35 GHz, 37.1 GHz, and 85.5 GHz.

AMSU

The Advanced Microwave Sounding Unit (AMSU) consists of a suite of 20 passive microwave radiometers. Two primary instruments, AMSU-A and AMSU-B, observe the earth in different parts of the microwave spectrum for different purposes.

AMSU-A

AMSU-A is a cross-track, line-scanned instrument designed to measure scene radiances in 15 discrete frequency channels which permit the calculation of the vertical temperature and moisture profile from about 3 millibars (~45 km) to the Earth's surface. Each scan has 30 cells, with a resolution of 3.3 degrees (50 km at nadir). The swath width is 2343 km (96.66 degrees). The AMSU-A instrument is made up of two separate modules, A1 and A2. AMSU-A1 contains the 13 highest frequencies (50.3 - 89 GHz) of various polarizations. AMSU-A2 contains the two lowest frequency channels (23.8 and 31.4 GHz), both vertically polarized.

ANEMOMETER

An instrument for measuring or indicating the force or speed of wind.

ANGSTROM EXPONENT

The name of the exponent in the formula that describes the dependency of the aerosol optical thickness on wavelength; The exponent is indicative of coarse (such as dust) vs. fine mode aerosols.

ANTENNA TEMPERATURE

Absolute radiometric temperature incident upon the instrument antenna with no corrections for spurious energy received from sources not intended by the instrument design.

APR-2

The Second Generation Airborne Precipitation Radar (APR-2) system includes a real-time pulse compression processor, a fully-functional control and timing unit, and a very compact LO/IF module, all of which could be used in spaceborne applications. The cylindrical reflector antenna and linear feed array for the spaceborne PR-2 have been replaced by traveling wave tube amplifiers (TWTAs), front-end electronics, and an offset parabolic reflector antenna with mechanical scanning. The APR-2 looks downward and scans its beam across-track, with each scan beginning at 25 degrees to the left of nadir and ending at 25 degrees to the right. It uses the same scanning antenna reflector as that used for the Airborne Rain Mapping Radar (ARMAR), which consists of a 0.4 m offset reflector antenna with a mechanically scanned flat plate. The APR-2 antenna feed is a dual-frequency feed (13.4 and 35.6 GHz) and the aperture at 35.6 GHz is under-illuminated to provide matched beams at the two frequencies. This choice results in poor Doppler accuracy at Ka-band, but is needed for rain retrieval.

AQUA

The Aqua satellite, launched 04 May 2002, is the continuing effort of NASA's Earth Science Enterprise (ESE) to observe and measure the state of the Earth system, while also monitoring global environmental changes over time. Aqua carries six state-of-the-art instruments in a near-polar low-Earth orbit. The six instruments are the Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU-A), the Humidity Sounder for Brazil (HSB), the Advanced Microwave Scanning Radiometer for EOS (AMSR-E), the Moderate-Resolution Imaging Spectroradiometer (MODIS), and Clouds and the Earth's Radiant Energy System (CERES). Each has unique characteristics and capabilities, and all six serve together to form a powerful package for making Earth observations. These data wil be processed into continuous long-term measures of the state of the atmosphere, land, and oceans.

ATMOSPHERIC CONDUCTIVITY

The measure of the atmosphere to allow the passage of electical current. Above 100m, atmospheric conductivity decreases, thus increasing the electic field.

ATMOSPHERIC LIQUID WATER

A measure of the columnar liquid water, as in clouds or rain, in the atmosphere in units of milligrams per square centimeter.

ATMOSPHERIC PRESSURE

The pressure exerted by the weight of air above a given point. Usually expressed in terms of the height of a column of mercury.

ATMOSPHERIC PRESSURE MEASUREMENTS

The pressure exerted by the weight of air above a given point. Usually expressed in terms of the height of a column of mercury.

ATMOSPHERIC SCATTERING RATIO

This relative aerosol measurement represents the total backscattering of aerosols and molecules divided by a molecular density profile, which was determined using a tropical molecular density profile derived from the Standard Atmosphere.

AVAPS

The Airborne Vertical Atmosphere Profiling System (AVAPS) uses dropwindsondes incorporating Global Positioning System (GPS) receivers to measure the atmospheric state parameters during their descent. Dropwindsondes measure vertical profiles of pressure, temperature, and humidity. Three dimensional position information from the GPS yields the vertical wind structure.

BACKSCATTER POWER

The scattering of radiant energy by aerosols (solid particles or liquid droplets) into the hemisphere of space bounded by a plane normal to the direction of the incident radiation and lying on the same side as the incident ray.

BAROMETER

An instrument used for determining atmospheric pressure. The two most common barometers are the mercury barometer and the aneroid barometer.

BOUNDARY LAYER TEMPERATURE

The conversion of kinetic energy into heat by work done against the viscous stresses in the boundary layer.

BRIGHTNESS TEMPERATURE

Effective temperature of a blackbody radiating the same amount of energy per unit area at the same wavelengths as the observed body; also called effective temperature.

C-STAR

The Conically-Scanning Two-look Airborne Radiometer is a passive microwave radiometer system on an airborne platform that collects data at 37.1 GHz. Making use of a rotating antenna, the C-STAR is able to produce images forward and aft of the aircraft ground track. Data is collected in both horizontal and vertical polarization for each of the forward and aft images.

CAMEX-1

The Convection and Moisture Experiments (CAMEX-1) were NASA funded experiments designed to study the three-dimensional moisture fields using satellite, aircraft, and ground-based instrumentation and the multifrequency radiometric and lightning signatures of tropical convection in support of the Mission to Planet Earth. The geographic domain of the CAMEX region was between 25 degrees North to 45 degrees North latitude and 70 degrees West to 83 degrees West longitude. 1993-09-08 through 1993-10-07.

CAMEX-2

The second Convection and Moisture Experiments (CAMEX-2) were NASA funded experiments designed to study the three-dimensional moisture fields using satellite, aircraft, and ground-based instrumentation and the multifrequency radiometric and lightning signatures of tropical convection in support of the Mission to Planet Earth. The geographic domain of the CAMEX region was between 25 degrees North to 45 degrees North latitude and 70 degrees West to 83 degrees West longitude. 1995-08-23 through 1995-09-02.

CAMEX-3

The Third Convection and Moisture Experiment (CAMEX-3). The Convection and Moisture Experiment (CAMEX) is a series of field research investigations sponsored by the Earth Science Enterprise of the National Aeronautics and Space Administration (NASA). The Third field campaign in the CAMEX series (CAMEX-3) was scheduled for 6 August through 23 September, 1998, to study tropical cyclone development, tracking, intensification, and landfalling impacts using NASA-funded aircraft and surface remote sensing instrumentation.

CAMEX-4

The Convection And Moisture EXperiment (CAMEX) is a series of field research investigations sponsored by the Earth Science Enterprise of the National Aeronautics and Space Administration (NASA). The fourth field campaign in the CAMEX series (CAMEX-4) ran from 16 August to 24 September, 2001 and was based out of Jacksonville Naval Air Station, Florida. CAMEX-4 focused on the study of tropical cyclone (hurricane) development, tracking, intensification, and landfalling impacts using NASA-funded aircraft and surface remote sensing instrumentation.

CAPE

The Convection and Precipitation/Electrification Experiment (CaPE) took place in central Florida with a latitude range of 43N, to 25.5N, westernmost longitude of 86W, and easternmost longitude of 69W. The CaPE Flight Activity began on July 18, 1991 and ended on Aug. 17, 1991. Making use of the Advanced Microwave Precipitation Radiometer (AMPR) on board on a NASA ER-2 aircraft flying at a nominal 20km altitude, passive microwave measurements were made of convective activity. The purpose of the experiment was to collect precipitation data in tropical convective storm cells over both water and land. Data returned included ice/water concentrations and amounts, and the structure of the convective cells.

CAPS

The Clouds, Aerosol and Precipitation Spectrometer (CAPS) is a combination of two optical sensors, the Cloud Imaging Probe (CIP) and the Cloud and Aerosol Spectrometer (CAS). The CAS uses forward-scatter and back-scatter techniques to measure particles from 0.5 micrometers to 50 micrometers. The CIP uses a fast 64-element photodiode array to generate 2-Dimensional Images of particles from 25-1550 micrometers.

CARBON MONOXIDE MIXING RATIO

The concentration of carbon monoxide (CO), a compound of carbon and oxygen containing one atom of oxygen in each molecule, colorless and odorless gas.

CEILOMETER

An automatic, recording, cloud-height indicator.

CLIMATOLOGY DATABASE

A collection of data from various sources measuring various parameters. Watershed data, for example, is comprised of rainfall information gathered from rain gauge networks and stream flow measurements which are used in conjunction with topographical information, vegetation and soil and ground permeability to determine the fate of water falling in a defined area. Data from these sources are collected over a period of years in order to better understand the long term patterns.

CLOCK

A source of regularly occurring pulses used to measure the passage of time.

CLOUD BASE

For a given cloud or cloud layer, the lowest level in the atmosphere at which the air contains a perceptible quantity of cloud particles.

CLOUD BASE TEMPERATURE

For a given cloud or cloud layer, the temperature at the lowest level in the atmopshere at which the air contains a perceptible quantity of cloud particles.

CLOUD CONDENSATION NUCLEI

Cloud particles as small as molecules and up in size through precipitation elements around which droplets condense in the atmosphere.

CLOUD HEIGHT

The height of a could measured from its base to the top

CLOUD LIQUID WATER

A measure of the columnar liquid water, as in clouds or rain, in the atmosphere in units of milligrams per square centimeter.

CLOUD LIQUID WATER/ICE

The amount of liquid water/ice crystals resident in clouds per unit volume of air.

CLOUD PARTICLE IMAGER

The cloud particle imager (CPI) is a probe that uses a three laser system for detection and imaging of particles passing through the system. It can image and count particles in the size range of 15-2500um.

CLOUD/RAIN LIQUID WATER

A measure of the columnar liquid water, as in clouds or rain, in the atmosphere in units of milligrams per square centimeter. Also includes rain indicator.

COLUMNAR WATER VAPOR

A measure of the columnar water vapor in the earth's atmosphere in grams per square centimeter.

CONDENSATION NUCLEI COUNTER

A particle counter which measures the number concentration of individual particles that are a specific diameter. Size measured depends on the characteristics of the specific instrument.

CRS

CRS (Cloud Radar System) is a coherent Doppler radar system at 94 GHz. CRS provides vertically profiled reflectivity and Doppler velocity at aircraft nadir along the flight track.

CVI

The NCAR counterflow virtual impactor is an airborne instrument used to measure cloud particle/droplets of a size greater than about 8 microns in diameter, and cloud condensation nuclei (CCN) by using a counter flow stream of dry nitrogen gas out of the tip of the probe. This flow is sufficiently strong to displace particles/droplets of smaller diameter. Once through the probe, water vapor and residual nonvolatile materials (CCN) are sampled and measured.

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