In the FIFE optical thickness cross-calibration study, all of the data were acquired on August 4 and 6, 1989, at a single location in Manhattan, Kansas, at the airport near the tarmac where the C-130 aircraft was parked.
In the FIFE optical thickness study, data were collected on nine days in June, July, and August 1987 and on three days in August 1989. The data are from flight lines that targeted selected locations within the FIFE study area near Manhattan, Kansas. The C-130 sunphotometer data cover an area between 38.73 degrees and 39.67 degrees North latitude and between 96.25 degrees to 97.81 degrees West longitude. Coverage is dependent on the type of mission flown (e.g., Coordinated Mision Plans 1, 2, 3). Flight lines vary in altitude from 504 to 26715 feet. The flight lines are oriented perpendicular and parallel to the solar plane, ideally with three lines in each direction. Flight headings therefore vary with each flight line as well as with each IFC as the solar position changes. Variability in atmospheric optical properties along some flight lines and substantial differences in atmospheric optical properties between June 6 and October 11, 1987 (Spanner et al., 1990), underscore the need to make quantitative measurements of atmospheric optical properties at the time of remote-sensing data acquisition.
The OTTER optical thickness study covered six Oregon sites across an elevational and climatic gradient. The transect began at the Pacific coast at the site called Cascade Head, passed through the outskirts of Corvallis, through a dense Douglas fir forest at Scio, through a mountain hemlock/subalpine fir community at Santiam Pass, through a Ponderosa pine community near Metolius, and ended at a site east of Sisters called Juniper. In all, the transect stretched some 300 km from west to east. Data were collected on June 19, 20, and 21, 1990, and on August 13 and 14, 1990.
In the 1983-84 SNF canopy reflectance study, data were collected from a 50 x 50 km area centered at approximately 48 degrees North latitude and 92 degrees West longitude in northeastern Minnesota, at the southern edge of the North American boreal forest. Data were collected and processed for three days: July 13 and August 6, 1983, and June 28, 1984.
In the FIFE optical thickness cross-calibration study, optical thickness data were collected simultaneously by the SXM-2, Reagan, and airborne tracking sunphotometers at the same site. Surface pressure was measured with a high-accuracy barometer made by Atmospheric Instrumentation Research, Inc.
In the FIFE optical thickness study, the data collection system was based on a Hewlett-Packard HP9816 computer with floppy disk and printer. This used data-collection, data-processing, and printing software developed by NASA Ames Research Center. 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 were sampled approximately every 2 sec and synchronized with the aircraft data system that provided the altitude, longitude, and latitude data. The science data set included the six detector signals, detector temperature, tracking error, sun tracker azimuth angle, sun tracker elevation angle, and UTC time (some of these parameters are not included in this FIFE data set). The computer stored the data on 3.5-inch floppy disks. The data were also printed out for real-time check and backup.
In the OTTER optical thickness study, the sensing technique used a shadow mask that bisects each detector when the system is in balance. This design allowed for very accurate tracking, yet at the same time provided a field of view of plus or minus twenty-five degrees. Each file in the dataset consisted of 23 fields of data. The first eight fields contained information about the measurement site, the index number of the sample, the PDT time, the solar time, the solar elevation, the air mass, the latitude, the longitude, and the altitude. The next six fields consist of the Rayleigh optical depths for the sample, and the following six fields consisted of the net optical depths for the sample. The final three fields gave such information about the measurement site as the atmospheric pressure, the 940 wavelenth transmission, and the amount of water vapor in the atmosphere. Information concerning data processing is not available.
Details on data acquisition are not available for the 1983-84 SNF canopy reflectance study study. Data were sorted by observation date and study site and several processing steps were required to turn raw TMS data into physically meaningful numbers for the test sites. The TMS scanner swept through view angles of plus or minus 50 degrees. This introduced both geometric distortions and varying atmospheric path lengths across the scan line. At extreme scan angles, a pixel covered an area on the ground several times larger than at nadir. At the nominal 5000-foot altitude flown, a nadir pixel covered 3.81 meters along the scan, expanding to 9.22 meters at 50 degrees off nadir. To compensate for this distortion, the data were linearly resampled to a constant pixel size, the same size as the nadir pixel. The scan angle corrected images from different flight lines were then registered to a common image. The registration algorithm used control points to remove distortions locally rather than globally and was effective in correcting for perturbations introduced by variations in aircraft motion. Sites were located in the imagery using photographs, descriptions of site locations, firsthand knowledge, and maps. Digital count values for areas of four by four pixels (approximately 16 by 16 meters) were extracted from each flight line. Using the calibration data provided for each scan line, these values were converted to radiance values by subtracting the low blackbody radiance count and multiplying by the radiance calibration factor. The TMS radiance values were converted to reflectance using values for insolation, atmospheric transmittance, and path scattered radiance for the appropriate solar and view angles. No measurement of these values were made, so the LOWTRAN6 atmosphere model was used to generate them. Scattering contributions calculated from the path between the canopy and the sensor were subtracted from the sensor-detected radiances and divided by the incident flux to generate reflectance factors.
On-line information is available from the following World Wide Web sites:
C-130 Airborne Laboratory Experimenter's Handbook (http://www.dfrc.nasa.gov/airsci/index.html)
FIFE NS001 TMS Extract Data Set Guide Document (http://www-eosdis.ornl.gov/FIFE/Datasets/Satellite_Observations/NS001_TMS_Extract_Data.html)
FIFE Optical Thickness Cross-Calibration Data Set Guide Document (http://www-eosdis.ornl.gov/FIFE/Datasets/Optical_Properties/optical_thick_calib.html)
FIFE Optical Thickness Data: C-130 Aircraft Data Set Document (http://www-eosdis.ornl.gov/FIFE/Datasets/Optical_Properties/optical_thick_c130.html)
Jenner, J. Ames Research Center: A Complete Service Center for Airborne Earth Observation. The Earth Observer. May/June, 1995.
(http://eospso.gsfc.nasa.gov/eos_observ/5_6_95/p09.html)Optical Thickness Data: Aircraft Dataset Document (http://www-eosdis.ornl.gov/OTTER/guides/Airborne_Sun_Photometer_Data.html)
SNF NS001-TMS Canopy Reflectance 1983-84: Data Set Guide Document (http://www-eosdis.ornl.gov/SNF/guides/ns001tms_canopy_reflect.html)
Revision Date: Friday, 10-Dec-2004 12:21:16 EST
URL: http://daac.ornl.gov/source_documents/c130.html