BOREAS RSS-12 Airborne Tracking Sunphotometer Measurements Summary The BOREAS RSS-12 team collected both ground and airborne sunphotometer measurements for use in characterizing the aerosol optical properties of the atmosphere during the BOREAS data collection activities. These measurements are to be used to: 1) measure the magnitude and variability of the aerosol optical depth in both time and space; 2) determine the optical properties of the boreal aerosols; and 3) atmospherically correct remotely sensed data acquired during BOREAS. This data set contains airborne tracking sunphotometer data that were acquired from the C-130 aircraft during its flights over the BOREAS study areas. The data cover selected days and times from May to September 1994. The data are stored in tabular ASCII files. Table of Contents * 1 Data Set Overview * 2 Investigator(s) * 3 Theory of Measurements * 4 Equipment * 5 Data Acquisition Methods * 6 Observations * 7 Data Description * 8 Data Organization * 9 Data Manipulations * 10 Errors * 11 Notes * 12 Application of the Data Set * 13 Future Modifications and Plans * 14 Software * 15 Data Access * 16 Output Products and Availability * 17 References * 18 Glossary of Terms * 19 List of Acronyms * 20 Document Information 1. Data Set Overview 1.1 Data Set Identification BOREAS RSS-12 Airborne Tracking Sunphotometer Measurements 1.2 Data Set Introduction The Airborne Tracking Sunphotometer (ATSP) data set consists of instrument voltages; Sun position information; ozone (O3), nitrogen dioxide (NO2) and aerosol optical depth values. These data were collected and processed by the BOReal Ecosystem-Atmosphere Study (BOREAS) Remote Sensing Science Team 12 (RSS- 12) at the National Aeronautics and Space Administration (NASA) Ames Research Center (ARC). The data provide a good characterization of atmospheric aerosols during the C-130 flights. 1.3 Objective/Purpose The overall goal of this investigation was to measure aerosol optical properties from both ground- and aircraft-based sunphotometers during the 1994 BOREAS Intensive Field Campaigns (IFCs). These measurements are to be used to: 1) Measure the magnitude and variability of the aerosol optical depth in both time and space. 2) Determine the optical properties of the boreal aerosols. 3) Atmospherically correct selected remotely sensed data acquired during BOREAS. 1.4 Summary of Parameters The phenomenon being measured is the atmospheric aerosol optical depth. The parameters include Rayleigh optical depth, aerosol optical depth, time, latitude, longitude, air mass, solar position, and aircraft altitude. 1.5 Discussion The ATSP data were used in conjunction with the Automated Ground Sunphotometer (AGSP) data to determine the magnitude and variability of the aerosol optical depth in both time and space. The aerosol optical depth data will be inverted using an algorithm developed by King et al., 1978, to derive the size distribution of the boreal aerosols. Mie theory will then be used to calculate the aerosol phase function and single-scattering albedo. Finally, the atmospheric correction algorithm of Wrigley et al., 1992 will be used to atmospherically correct selected NS001 Thematic Mapper Simulation (TMS), Landsat Thematic Mapper (TM), and MODerate-resolution Imaging Spectrometer (MODIS) Airborne Simulator (MAS) data collected during the 1994 BOREAS IFC's. Atmospheric correction of Landsat TM and other satellite data will use the aerosol properties derived from surface optical depth measurements. Atmospheric correction of NS001 and MAS data will use aerosol properties derived from the airborne optical depth measurements as well as those from the surface measurements. 1.6 Related Data Sets BOREAS RSS-12 Automatic Ground Sunphotometer Measurements in the SSA BOREAS RSS-11 Ground Network of Sunphotometer Measurements BOREAS RSS-18 Ground Sunphotometer Measurements in the SSA 2. Investigator(s) 2.1 Investigator(s) Name and Title Robert C. Wrigley (retired 1995) Principal Investigator Co-Investigators: Michael A. Spanner Robert E. Slye Philip B. Russell John M. Livingston 2.2 Title of Investigation Aerosol Determinations and Atmospheric Correction for BOREAS Imagery 2.3 Contact Information Contact 1 -------------------------------- Michael A. Spanner Co-Investigator Johnson Controls World Services NASA Ames Research Center Moffett Field, CA (415)604-3620 mspanner@gaia.arc.nasa.gov Contact 2 ------------------------------- Jaime Nickeson NASA/GSFC Greenbelt, MD (301) 286-3373 (301)286-0239(fax) Jaime.Nickeson@gsfc.nasa.gov 3. Theory of Measurements The ATSP measures direct-beam solar radiation for six channels in the visible and near-infrared wavelengths. The solar radiation data are collected in the form of voltages. The instrument was calibrated before and after the experiment at high mountain observatories, which often have clean, stable air masses, so the Langley plot technique could be used. For calibration, data are collected at a range of solar angles from low solar elevation (air mass=5) to high solar elevation (air mass =1.8). A regression is developed between log voltage and air mass. This regression equation is then extrapolated to an air mass of 0. This value called the zero air mass intercept voltage, is the value used to calibrate the instrument in a given channel. Great care must be taken to ensure the stability of these intercept voltages over time. A calibration history is maintained that attests to the stability of the instrument. The voltages measured by the instrument during the BOREAS IFCs were converted to total optical depth using the zero air mass intercept voltages calculated from the calibrations using the equation: V/Vo = (Rm/R)^2 exp(-mt) where V is the measured voltage, Vo is the zero air mass voltage intercept, R is the radius of Earth's orbit at the time, Rm is the mean radius, m is the air mass at the time, and t is the total optical depth (usually written as the Greek letter tau). The aerosol optical depth is calculated from the total optical depth by subtracting a number of components that contribute to the total optical depth: Rayleigh scattering and gaseous absorption due to ozone and NO2. The Rayleigh optical depth is calculated using pressure measured on the aircraft. NO2and ozone optical depths are subtracted from the total minus Rayleigh optical depth to obtain the aerosol optical depth. NO2 abundance is obtained from climatology tables based on Noxon, 1979, and convolved with absorption coefficients at ATSP wavelengths. Ozone optical depth is calculated using ozone abundances from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument and convolved with absorption coefficients at ATSP wavelengths. The result of this processing is the aerosol optical depth measured in five channels (not including the 940 nm water vapor channel) at approximately 2-second intervals in the air and 10 second intervals on the ground. The correction of remote sensing data acquired from satellites or aircraft for effects due to the intervening atmosphere has proven to be a difficult problem. Not only does the atmosphere reduce the transmission of the incoming, reflected, and emitted radiation, but it contributes reflected and emitted radiation of its own. Under high aerosol concentration conditions, atmospheric radiation comprises over 90% of the satellite-observed radiance, but even much smaller effects would degrade the quantitative use of these data unless they are taken into account. The interaction of radiation with the atmosphere is complex and has proved difficult to calculate without reference to measurements made at, or close to, the time and location of interest. Effects due to Rayleigh scattering from atmospheric gases are well understood because the major gases (nitrogen, oxygen) that comprise 99% of the atmosphere are well mixed and their concentrations with altitude are known. The effects because of small particle (aerosol) scattering are quite variable because of the wide range of aerosol concentrations; and the variety of aerosols found in the atmosphere. Because aerosol concentrations cannot be known a priori, they must be measured at the time and location of remote sensing data acquisition. The physical properties of aerosols such as size, shape, refractive index, and concentration in the atmosphere control the aerosol interaction with light according to a set of optical properties. Three fundamental properties are (1) the aerosol optical depth, an indirect measure of the size and number of particles present in a given column of air; (2) the single scattering albedo; the fraction of light intercepted and scattered by a single particle; and (3) the phase function; a measure of the light scattered by a particle as a function of angle with respect to the original direction of propagation. 4. Equipment 4.1 Sensor/Instrument Description The instrument consists of a solar-tracking system, detector module, temperature control system, nitrogen-purge system, mechanical drive chain, and data collection system. 4.1.1 Collection Environment The ATSP was used for data collection while mounted on the NASA C-130 aircraft. Data were collected while the aircraft was on the ground and during flight at altitudes up to 10,120 meters. 4.1.2 Source/Platform The ATSP was mounted on the NASA ARC C-130 Earth Resources aircraft. 4.1.3 Source/Platform Mission Objectives The ATSP was developed to obtain accurate multispectral atmospheric extinction measurements at different altitudes. 4.1.4 Key Variables The primary quantity being measured is the total optical depth. The aerosol optical depth is derived by subtracting optical depths caused by other components of the atmosphere: Rayleigh scattering, ozone absorption, and NO2 absorption. 4.1.5 Principles of Operation The sensors used are Clairex photoresistors that have been matched to track each other over the operational range of Sun intensities. The sensing technique uses a shadow mask that bisects each detector when the system is in balance. The design allows for very accurate tracking, yet at the same time provides a Field- of-View (FOV) and accurate tracking in a very compact package. The dome rotation is referred to as azimuth motion. The central section of the dome is free to rotate within the dome, perpendicular to the azimuth, and is referred to as elevation motion. The control system is designed to compensate for the flight characteristics of the aircraft. 4.1.6 Sensor/Instrument Measurement Geometry The six separate detectors view the Sun simultaneously at six independent wavelengths. The FOV of each detector is set by the entrance aperture to 4 degrees; the inside surfaces of the aperture assembly are anodized a dull black to reduce internal reflections. The 4-degree FOV was selected to allow for +/-1 degree of tracking error without affecting the solar-radiation signal. The wavelengths and the full width half maximum (FWHM) of the ATSP are shown in the following table for all channels. Wavelength (nm) FWHM (nm) --------------- --------- 379.8 11.0 451.3 6.2 525.7 9.1 860.5 13.0 940.0 0.2 1059.9 12.7 The system is designed to move in elevation or azimuth at 8 degrees per second. The acceleration that may occur during a turn is estimated to be 1.0 radian per second squared. If the instrument should lose lock, the reacquisition occurs very rapidly as long as the Sun is in the FOV of the instrument. The tracking system responds quickly because it uses a single rate of 8 degrees per second for tracking. The solar-tracking system was designed to achieve two objectives: first, to be able to acquire the Sun starting from a position several degrees away; and second, to track the Sun with an accuracy of +/-2 degrees in the presence of aircraft movements. 4.1.7 Manufacturer of Sensor/Instrument Manufactured by NASA ARC, Moffett Field, CA 94035, Dr. Philip Russell, Principal Investigator. 4.2 Calibration 4.2.1 Specifications The detectors are temperature controlled, and the amplifier gains are set with precision resistors. The resolution of the detector signals is limited by the 12-bit analog-to-digital converter that can resolve 1 part out of 2048 of the 0 to +10v detector signals. The instrument is designed to operate in clear skies, and it is assumed that over the period of a flight profile, there are no solar fluctuations. 4.2.1.1 Tolerance There is evidence in the literature that in the wavelength region of interest, solar fluctuations would account for less than a 1% variation of the data. 4.2.2 Frequency of Calibration The instrument was calibrated at the Mt. Lemmon Steward Observatory, Tucson, AZ, in April 1994 (before the field season) and at the Mauna Loa Observatory, HI in November 1994 (after the field season). 4.2.3 Other Calibration Information The calibration coefficients, corrected for Earth-Sun distance, are contained in the data files. 5. Data Acquisition Methods The data collection system was based on a Hewlett-Packard HP9816 computer with floppy disk and printer. This system was used to run data collection, data processing, and printing software developed by NASA ARC. In addition to the computer, the data collection system included a multiplexer, a 12-bit analog-to -digital converter, and electronics to process the aircraft inertial navigation data. The data are sampled approximately every 2-seconds and are synchronized with the aircraft data system, which provides the altitude, longitude, and latitude data. The science data set includes the six detector signals, detector temperature, tracking error, Sun tracker azimuth angle, Sun tracker elevation angle, and Universal Time Code (UTC) time. The data were stored on 3.5-inch floppy disks and were also printed for real-time check and backup. Data were collected for the duration of the optical flights of the C-130 aircraft and were collected on the ground before and/or after the flights to determine the total atmospheric aerosol optical depth. A new data collection system is under design and construction. It will be based on a 486 laptop PC running Visual Basic in a Windows environment. Digital-to - analog conversion will be significantly enhanced and optimized for each channel using a Dacbook. Data reduction will be simplified because the necessity for hex-to-ASCII conversion will be eliminated. Several programs currently requiring processing on minicomputers will be installed on the PC; this will permit processing to semifinal products in the field (only the postmission calibration will have to be incorporated into the final products). 6. Observations 6.1 Data Notes Below is a table of SPATIAL_COVERAGE C130_SITE C130_LINE_NUM -------------------- --------- ------------- SSA 429 0 SSA-LAKE 429 9 SSA-LAKE 429 10 SSA-OBS 429 101 SSA-OBS 429 102 SSA-OBS 429 103 SSA-OJP 429 201 SSA-OJP 429 202 SSA-OJP 429 203 SSA-9OA 429 301 SSA-9OA 429 302 SSA-9OA 429 303 SSA-YJP 429 401 SSA-YJP 429 402 SSA-YJP 429 403 SSA-9YA 429 501 SSA-9YA 429 502 SSA-9YA 429 503 SSA-CAL 429 601 SSA-CAL 429 603 SSA-FEN 429 701 SSA-FEN 429 702 SSA-FEN 429 703 SSA 430 0 SSA-MSA 430 1 SSA-MSA 430 2 SSA-MSA 430 3 SSA-MSA 430 4 SSA-MSA 430 5 SSA-MSA 430 6 SSA-MSA 430 7 SSA-MSA 430 8 SSA-MSA 430 9 SSA-MSA 430 10 SSA-MSA 430 11 NSA 431 0 CALIB_FROZEN_LAKE KE 431 1 NSA-OBS 431 101 NSA-OBS 431 102 NSA-OBS 431 103 NSA-FEN 431 201 NSA-FEN 431 202 NSA-FEN 431 203 NSA-OJP 431 301 NSA-OJP 431 302 NSA-OJP 431 303 NSA-YJP 431 401 NSA-YJP 431 402 NSA-YJP 431 403 NSA-9OA 431 601 NSA-9OA 431 602 NSA-9OA 431 603 NSA 432 0 NSA-MSA 432 1 NSA-MSA 432 2 NSA-MSA 432 3 NSA-MSA 432 4 NSA-MSA 432 5 NSA-MSA 432 6 NSA-MSA 432 7 NSA-MSA 432 8 NSA-MSA 432 9 TRANSECT 433 0 TRANSECT 433 1 TRANSECT 433 2 TRANSECT 433 3 TRANSECT 433 4 TRANSECT 433 5 NSA-MSA 999 999 NSA BTW 0 SSA BTW 0 NSA DSC 0 SSA DSC 0 TRANSECT DSC 0 NSA PRE 0 SSA PRE 0 TRANSECT PRE 0 TRANSECT TRN 0 SSA YPA 0 NSA YTH 0 6.2 Field Notes The ATSP operator normally takes notes of significant events while the instrument is acquiring data. These notes supplement the real-time display of detector voltages or optical depths and permit determination of the presence of variable cloud interference with remote sensing data collection; this feature often indicates whether or not a given flight line was acceptable or had to be repeated. If the line was acceptable, then the notes, if any, help identify data problems during processing. Anyone interested in these notes should contact RSS-12 personnel at NASA ARC. 7. Data Description 7.1 Spatial Characteristics The ATSP views the Sun with a 4-degree FOV and typically acquires data every 2 or 3 seconds during flight. A typical ground speed of the C-130 aircraft is 150 m/sec. Hence, data are collected every 300 meters along a flight line. During spiral descents and ascents, typical vertical rates are 1,000 ft/min or 5 m/sec so the ATSP samples the vertical column every 10 meters. 7.1.1 Spatial Coverage Although most of the data were collected over the BOREAS Northern Study Area (NSA), Southern Study Area (SSA), and tower sites, some data are available over the transect between the NSA and SSA. The North American Datum 1983 (NAD83) corner coordinates of the 1,000- by 1,000- km BOREAS region are: Latitude Longitude ---------- ----------- Northwest 59.97907 N 111.00000 W Northeast 58.84379 N 93.50224 W Southwest 51.00000 N 111.00000 W Southeast 50.08913 N 96.96951 W The NAD83 corner coordinates of the NSA are: Latitude Longitude -------- --------- Northwest 56.249 N 98.825 W Northeast 56.083 N 97.234 W Southwest 55.542 N 99.045 W Southeast 55.379 N 97.489 W The NAD83 corner coordinates of the SSA are: Latitude Longitude -------- --------- Northwest 54.321 N 106.228 W Northeast 54.225 N 104.237 W Southwest 53.515 N 106.321 W Southeast 53.420 N 104.368 W 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution The sunphotometer's spatial resolution was variable based on aircraft maneuvers and flight speed. If the sunphotometer was acquiring data every 2-seconds and the C-130 was flying level at 150 m/sec, then the ground resolution was 300 meters. 7.1.4 Projection The coordinates in the data files are from the C-130 internal navigation system (INS). The INS geographic position data are from the onboard Global Positioning System (GPS), which uses NAD83. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage Data were acquired during three IFCs in 1994. The days and times were: Date Time (GMT) ----------- ----------------- 25-May-1994 15:21:28-18:02:23 26-May-1994 12:51:41-19:15:20 31-May-1994 13:30:20-16:30:26 01-Jun-1994 13:34:43-15:20:41 04-Jun-1994 13:08:07-18:53:02 06-Jun-1994 15:07:25-17:33:26 07-Jun-1994 14:15:28-17:08:53 08-Jun-1994 14:04:34-22:29:33 20-Jul-1994 15:12:04-18:25:55 21-Jul-1994 13:46:30-17:33:00 22-Jul-1994 14:04:43-17:27:18 23-Jul-1994 13:44:38-14:41:09 24-Jul-1994 13:50:45-14:08:24 26-Jul-1994 16:08:00-17:15:44 29-Jul-1994 13:21:03-18:16:19 31-Jul-1994 12:59:18-18:24:25 02-Aug-1994 13:09:15-18:07:19 03-Aug-1994 14:37:00-16:46:39 04-Aug-1994 12:45:25-22:23:19 08-Aug-1994 12:47:45-15:43:01 09-Aug-1994 12:36:04-19:20:08 10-Aug-1994 13:21:34-18:08:37 31-Aug-1994 14:05:24-19:55:39 01-Sep-1994 00:40:38-14:27:32 02-Sep-1994 13:51:45-17:10:32 03-Sep-1994 14:08:56-16:53:50 06-Sep-1994 15:03:13-18:33:01 08-Sep-1994 14:02:31-17:41:14 09-Sep-1994 15:49:51-16:00:32 7.2.2 Temporal Coverage Map Not available. 7.2.3 Temporal Resolution The ATSP typically samples every 2 or 3 seconds during flight, but the sampling rate is under computer control and can be modified if necessary. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (sunphair.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (sunphair.def). 8. Data Organization 8.1 Data Granularity All of the Airborne Tracking Sunphotometer Measurement Data are contained in one file. 8.2 Data Format(s) The data file contains numerical and character fields of varying length separated by commas. The character fields are enclosed with single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition files (sunphair.def). 9. Data Manipulations 9.1 Formulae For all sunphotometer channels except the 940 nm, the Bouguer-Lambert-Beer extinction law was used to describe the attenuation of solar radiation: V = (R'/R)^2 V0 exp(-m tau) = V'0 exp(-m tau) where V is the output voltage of the detector at a given wavelength, V0 is the zero air-mass voltage intercept at that wavelength for the mean Earth-Sun separation R', R is the Earth-Sun separation at the time of observation, m is the atmospheric air mass between the instrument and the Sun, tau is the wavelength-dependent total vertical optical depth above the sunphotometer, and V'0 is the zero-air-mass voltage intercept for the Earth-Sun separation R at the time of observation. The 940-nm channel requires different processing and is not included this data set. The logarithm of the above equation, ln V = ln V'0 - m tau, is used in calibration to provide the V'0 values for each channel (i.e., zero air mass Langley plot intercept voltages). When the detector voltages are plotted against the air mass, the intercept is the V'0. After calibration, this equation can be solved for tau to provide the total optical depth. The total optical depth is then decomposed using tau = tau_r + tau_a + tau_O3 + tau_NO2 + tau_H2O, where these terms are the optical depth due to Rayleigh scattering, aerosols, ozone, NO2, and water vapor, respectively. The source for each of these terms is given in Section 7.3. Water vapor was ignored because it contributes in the 940- nm channel. This description is taken from Spanner et al., 1990, where more information concerning the data processing can be found. 9.1.1 Derivation Techniques and Algorithms A description of algorithms can be found in Spanner et al., 1990. 9.2 Data Processing Sequence 9.2.1 Processing Steps The steps for processing are as follows: 1) acquire the data; 2) run a program to calculate all the variables, including solar zenith angle, air mass, Rayleigh optical depth, and instantaneous optical depth (total optical depth minus Rayleigh optical depth); 3) calculate NO2 and ozone optical depths from Noxon et al., 1979, and TOMS data, respectively; and 4) subtract NO2 and ozone to derive aerosol optical depth. The ozone abundance was determined from the TOMS satellite instrument convolved with ozone absorption coefficients from Penney (1979). The values calculated for NO2 and ozone optical depth were subtracted from the instantaneous optical depth to derive the aerosol optical depth, are provided in the data files. 9.2.2 Processing Changes None given. 9.3 Calculations 9.3.1 Special Corrections/Adjustments No special corrections or adjustments have been made. 9.3.2 Calculated Variables Description of algorithms can be found in Spanner et al., 1990. 9.4 Graphs and Plots Plots have been provided to BORIS and can be made available upon request. 10. Errors 10.1 Sources of Error Calibration errors are the main source of error in the derivation of aerosol optical depth. 10.2 Quality Assessment 10.2.1 Data Validation by Source Data were compared with the RSS-11 field sunphotometer (see related data sets, Section 1.6). 10.2.2 Confidence Level/Accuracy Judgment The data are of high quality, because a good calibration of the instrument was performed before and after the BOREAS field collection effort. 10.2.3 Measurement Error for Parameters Uncertainties for the aerosol optical depths were determined by using uncertainty propagation through the algorithm. The aerosol optical depth uncertainty is dependent on the uncertainty in the Rayleigh, ozone, and NO2optical depths, as well as the uncertainty in the intercept voltage (calibration error), instantaneous measurement, and airmass. Aerosol optical depth uncertainties are given in the data files and are summarized in Section 7.3 of this document. 10.2.4 Additional Quality Assessments None. 10.2.5 Data Verification by Data Center Visual review and use of selected subsets of the data have shown them to be of good quality with no noteworthy problems. 11. Notes 11.1 Limitations of the Data None. 11.2 Known Problems with the Data None. 11.3 Usage Guidance The values of aerosol optical depth are accurate instantaneous values of aerosol optical depth. These data were taken frequently; therefore, under conditions of rapid variability in cloudiness or haze, the data may not be internally consistent or appropriate. It is useful to calculate averages of aerosol optical depth over periods of time to get a more accurate measure of the average conditions at a site. Users should take note that the daily extrated files have a large size range (400 to 38,000 records) 11.4 Other Relevant Information The aerosol optical depth at 941 nm was not calculated because this channel primarily measures absorption due to water vapor. 12. Application of the Data Set These data can be used for correcting various visible and infrared satellite and aircraft image products or for characterizing the atmospheric aerosols at the times of the flights. 13. Future Modifications and Plans Future plans for the airborne instrument include the design and development of a new 14-channel airborne instrument. 14. Software 14.1 Software Description NASA ARC software was developed in FORTRAN on a VAX to implement the data processing procedure described in Section 9.1. Input data include sunphotometer data files as well as ozone and NO2 optical depth parameters. Aerosol optical depths were calculated and written to the data files. No special software is needed to read the data files because they are stored comma delimited. 14.2 Software Access This software is used to generate the data product from the detector voltages and is not needed to use the data. 15. Data Access 15.1 Contact Information Ms. BethNelson BOREAS Data Manager NASA GSFC Greenbelt, MD (301) 286-4005 (301) 286-0239 (fax) beth@ltpmail.gsfc.nasa.gov 15.2 Data Center Identification See Section 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or fax. 15.4 Data Center Status/Plans The RSS-12 C130 sunphotometer data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center(DAAC). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory Oak Ridge, TN (423) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 16. Output Products and Availability 16.1 Tape Products None. 16.2 Film Products None. 16.3 Other Products The data are available as tabular ASCII files. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation None. 17.2 Journal Articles and Study Reports Bruegge, C.J., R.N. Halthore, B. Markham, M. Spanner, and R. Wrigley. 1992. Aerosol optical depth retrievals over the Konza prairie. Journal of Geophysical Research 97(D17):18743-18758. King, M., D. Bryne, B. Herman, and J. Reagan. 1978. Aerosol size distributions obtained by inversion of spectral optical depth measurements. J. Atmos. Sci. 35:2153-2167. Noxon, J. 1979. Stratospheric NO2, 2, Global behavior, J. Geophys. Res. 84:5067- 5076. Penney, C.M. 1979. Study of temperature dependence of the Chappuis band absorption of ozone, NASA Contract Rep. 158977, General Electric Company, Schenectady, N.Y. Russell, P., J. Livingston, E. Dutton, R. Pueschel, J. Reagan, T. DeFoor, M. Box, D. Allen, P. Pilewskie, B. Herman, S. Kinne, and D. Hofmann. 1994. Pinatubo and pre-Pinatubo optical depth spectra: Mauna Loa measurements, comparisons, inferred particle size distributions, radiative effects, and relationship to lidar data. J. Geophys. Res. 98:22,969-22,985. Sellers, P.and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P.and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P.and F. Hall and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P., F. Hall and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J.Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and early results from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. Sellers, P.and F. Hall. 1997. BOREAS Overview Paper. JGR Special Issue (in press). Spanner, M., R. Wrigley, R. Pueschel, J. Livingston, and D. Colburn. 1990. Determination of atmospheric optical properties for the First ISLSCP Field Experiment (FIFE). Journal of Spacecraft and Rockets 27:373-379. Wrigley, R.C., M.A. Spanner, R.E. Slye, R.F. Pueschel, and H.R. Aggarwal. 1992. Atmospheric correction of remotely sensed image data by a simplified model. Journal of Geophysical Research 97(D17):18797-18814. Young, A. 1980. Revised depolarization corrections for atmospheric extinction. Applied Optics 19:3427-3428. 17.3 Archive/DBMS Usage Documentation 18. Glossary of Terms air mass - secant of the solar zenith angle optical depth - an indirect measure of the size and number of particles present in a given column of air, which is a measure of the extinction of the direct solar beam by aerosols and particulates in the atmosphere, or by scattering. Also referred to as optical thickness. phase function - a measure of the light scattered by a particle as a function of angle with respect to the original direction of propagation radiometer - an instrument for measuring radiant energy Rayleigh - wavelength-dependent scattering directly proportional scattering to (1 + cos2(angle)) and indirectly proportional to wavelength4 single - the fraction of light intercepted and scattered by a scattering single particle albedo 19. List of Acronyms AGSP - Automated Ground Sunphotometer ARC - Ames Research Center ATSP - Airborne Tracking Sunphotometer BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOReas Information System DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System FIFE - First ISLSCP Field Experiment FOV - Field-of-View FWHM - Full Width Half Maximum GMT - Greenwich Mean Time GPS - Global Positioning System GSFC - Goddard Space Flight Center IFC - Intensive Field Campaign INS - Inertial Navigation System ISLSCP - International Satellite Land Surface Climatology Project MAS - MODIS Airborne Simulator MODIS - MODerate-resolution Imaging Spectrometer NASA - National Aeronautics and Space Administration NSA - Northern Study Area ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park RSS-12 - Remote Sensing Science Team 12 SSA - Southern Study Area TM - Thematic Mapper TMS - Thematic Mapper Simulator TOMS - Total Ozone Mapping Spectrometer URL - Uniform Resource Locator UTC - Universal Time Code 20. Document Information 20.1 Document Revision Dates Written: 07-Jan-1997 Last Updated: 04-May-1998 20.2 Document Review Dates BORIS Review: 19-May-1997 Science Review: 27-Jun-1997 20.3 Document ID 20.4 Citation Please acknowledge the NASA/ARC investigation (RSS-12) and Michael Spanner, Principal Investigator, if these data are used or referenced. If appropriate, the references cited in Section 17 may be used. 20.5 Document Curator 20.6 Document URL Keywords --------------- Aerosols Optical Thickness Ozone RSS12_Air_Sunphoto.doc 05/26/98