These data sets provide a measurement of the atmospheric optical properties over the FIFE site during June, July, and August of 1987, and August of 1989. Particular emphasis was given to obtaining measurements of the aerosol contribution to the total optical thickness of the atmosphere at a variety of wavelengths. These data sets use a variety of ground-based and airborne sun tracking sunphotometers and solar transmissometers. Because of discrepancies detected between the data collected by different instruments in 1987 an inter-calibration effort was undertaken in 1989. For this effort, inter-comparison measurements were made using the Reagan sunphotometer, an SXM-2 solar transmissometer, and the C-130 sunphotometer. These data were collected to enable atmospheric corrections of remote sensing data collected during FIFE. The atmospheric correction algorithm developed by Fraser, et al. is also included on the CD-ROM.

This data set contains optical thickness measurements made from a tracking sunphotometer installed atop NASA's C-130 earth remote sensing aircraft. They include Rayleigh optical depth and aerosol optical depth at 5 wavelengths (380, 450, 526, 600 and 1020 nm), atmospheric pressure and air mass, and transmittance at 940 nm. The flightlines on which these data were collected were flown on nine days in 1987 and three days in 1989. Substantial differences in atmospheric optical properties occurred on June 6 and October 11, 1987. Some of the transects for these optical measurements coincided with the Push Broom Mircrowave Radiometer (PBMR) transects, although these two instruments were not related. The grid lines and flight directions that were flown were coincident with satellite overpasses.

This data set contains measurements of aerosol optical depth computed from data collected with a ground-based sunphotometer that measures at eight discrete wavelengths (440, 522, 557, 613, 672, 781, 871, and 1030 nm) throughout the visible and near infra-red portion of the electromagnetic spectrum. Measurements of atmospheric pressure and ozone content are also included. These ground measurements were collected on ten days from June 25, 1987 to July 14, 1987, and on 13 days from July 25, 1989 to August 12, 1989, from two locations within the FIFE site. These data are used to provide atmospheric correction of remotely sensed data using radiative transfer models and to study aerosol particle size distribution. The algorithm developed to calculate the atmospheric corrections is described in a NASA Technical Memorandum that is found in the scanned documents section of this CD-ROM. The FORTRAN source code for the algorithm is in the "Grab Bag" directory.

This data set contains measurements of aerosol optical depth, ozone content, and Rayleigh scattering computed from data collected with ground-based Reagan and NIP sunphotometers that measure at ten (370, 400, 440, 520, 670, 780, 870, 1030, 610, 940 nm) and six (485, 560, 660, 830, 1650, and 2200 nm) discrete wavelength bands, respectively, throughout the visible and near infra-red portion of the electromagnetic spectrum. These data were collected on both clear and cloudy days. Measurements of atmospheric pressure, surface temperature, and a computed value for total optical thickness of the atmosphere are included in this data set. Ground measurements using the NIP (Normal Incident Pyrheliometer) sunphotometer were taken during the first FIFE intensive field campaign, May 30 through June 6, 1987. There are five days of measurements during this spring period when the grassland was growing rapidly. During the other four intensive field campaigns (three in 1987 and one in 1989) data were collected using the Reagan instrument. There are about six days of data in each of these campaigns. Data were collected from several stations within the FIFE site. These data are used to provide atmospheric correction of remotely sensed data using radiative transfer models and to study aerosol particle size distribution.

This data set contains measurements of aerosol, ozone, and Rayleigh optical thickness computed from data collected with ground-based sunphotometers that measured at four discrete wavelength bands from 380 to 945 nm. These data were collected on both clear and cloudy days. They were analyzed using the Langley technique, whereby Rayleigh optical depth is subtracted and the abundance of aerosol, ozone, and water vapor are measured simultaneously. In retrieving ozone a Junge aerosol model was assumed, thus the natural log of aerosol optical depth is linear with wavelength. Measurements of atmospheric pressure at the ground and the computed total optical thickness of the atmosphere are also included in this data set. Ground measurements were made at several stations within the FIFE site and were collected more or less continuously from February 1987 through October 1989. Data from March 6 through August 9, 1987 collected by the RMAS instrument is of questionable quality, since particles of shipping materials were found in the optical tube on the ninth of August. These data can be used to atmospherically correct remotely sensed data using radiative transfer models and to study aerosol particle size distribution.

This data set was collected so that the various sunphotometers (solar transmissometers) used in 1989 during the FIFE field campaign by different experimental groups could be inter-calibrated. The instruments were co-located in space and time so that a direct comparison could be made of the aerosol optical thickness derived by these groups and their instruments. Measurements were taken with three instruments (Solar transmissometer SXM-2, Reagan sunphotometer, and Airborne Tracking Sunphotometer) positioned side by side on August 4, 1989. Only the SXM-2 and Reagan sunphotometer were used for measurements on August 6, 1989. Optical thickness was measured for each of the instruments. All instruments followed the same temporal profile during the times they were simultaneously taking data, and data were on average in agreement to within 0.005 absolute optical thickness.

There are three aspects of the data in this data group which are noteworthy. First, all of the instruments used to collect the data described here are constant temperature detectors and they have autotracking or peak hold features. The instruments often used for measurements of optical thickness often suffer from the side effects which arise when these features are not available. Second, water column abundances are provided in the Bruegge data set (Optical Thickness Data from the Normal Incident Pyrheliometer (NIPS) and Reagan Sunphotometer). Lastly, the calibration data set provides a rare, direct comparison of three different instruments used to measure atmospheric optical thickness under identical conditions.

The confidence of these data is generally very good. The inter-calibration data set indicates that the data from all the instruments except the NIP sunphotometer used in IFC 1 (Bruegge data set) have a 1% uncertainty in calibration, which yields an absolute uncertainty of 0.01 per unit airmass for aerosol optical thickness. The NIP sunphotometer used in IFC 1 had a higher absolute uncertainty of about 0.05 per unit airmass. The uncertainties associated with ozone and Rayleigh optical thickness are thought to be negligible for the conditions encountered during the FIFE. Although the overall confidence is good for these data, there are specific time periods, instruments, and instrument channels for which the data are questionable. Specifically, the data collected between February 1987 and August 1987 using the RMAS sunphoTometer, given in the GSFC data set, are known to have been affected by particles of packing materials found within the optical tube of this instrument. Specific wavebands on some of the instruments used to collect the data in the GSFC data set are also known to have calibration problems (i.e., the 380-nm and 940-nm wavebands).

The optical thickness data sets described here have contributed to three areas of research in the distribution and formation of atmospheric aerosols. First, the data collected by Bruegge and Wrigley demonstrate that aerosols vary spatially in both the horizontal and vertical dimension, as well as temporally. These studies found that the horizontal and vertical variations are on the scale of kilometers, while the temporal variability occurs both diurnally and from day to day (Bruegge, et al. 1992a; Spanner, et al. 1990). Moreover, the data collected by Bruegge (Bruegge, et al. 1992b) and the associated research demonstrate that the total abundance of water vapor throughout an atmospheric column can be derived from measurements of solar radiation at or near 940 nm. This research result is particularly useful because it offers a cost-effective alternative to the conventional method of obtaining these data using disposable radiosonde packages. Finally, the data of Fraser demonstrates that the origin and growth of aerosols is especially sensitive to meteorological conditions such as continental and Gulf air masses (Halthore, et al. 1992a).

In addition, these optical thickness data sets have enabled the direct comparison of reflectance computed from remotely sensed data and reflectance derived from direct ground measurements. Using these sunphotometer derived optical thicknesses, atmospheric corrections were performed on Landsat TM images to derive ground reflectance values which were then compared with the ground-based sunphotometer measurements available in the data sets described (Wrigley, et al. 1992; Markham, et al. 1992). Data from the Cosmos 1939 satellite was also atmospherically corrected using these data and then used to derive land surface parameters such as leaf area index and biomass (Kozoderov, et al. 1992).

Bruegge, C.J., R.N. Halthore, B.L. Markham, M. Spanner, and R. Wrigley. 1992a. Aerosol optical depth retrievals over the Konza Prairie. J. Geophys. Res. 97:18743-18758.

Bruegge, C.J., J.E. Conel, R.O. Green, J.S. Margolis, G. Toon and R.G. Holm. 1992b. Water-vapor column abundance retrievals. J. Geophy. Res. 97:18759-18768.

Fraser, R.S., R.A. Ferrare, Y.J. Kaufman, S. Mattoo. 1989. Algorithm for atmospheric corrections of aircraft and satellite imagery. J. Int. Remote Sens. 13:541-557.

Halthore, R.N., C.J. Bruegge, and B.L. Markham. 1990. Aerosol optical thickness measurements during FIFE '89. Presented at the AMS Symposium on the First ISLSCP Field Experiment (FIFE), Anaheim, CA.

Halthore, R.N., B.L. Markham, R. Ferrare, and O. Aro. 1992a. Aerosol optical properties over the mid-continental United States. J. Geophy. Res. 97:18769-18778.

Halthore, R.N., and B.L. Markham. 1992b. Overview of Atmospheric Correction and radiometric calibration efforts during FIFE. J. Geophys. Res. 97:18731-18742.

Kozoderov, V.V., N.M. Vandysheva, A.V. Maslov, A.S. Panfilov, and L.A. Vedeshin. 1992. Cosmos 1939 data processing for FIFE 1989. J. Geophys. Res. 97:18779-18784.

Markham, B.L., R.N. Halthore, and S.J. Goetz. 1992. Surface reflectance retrieval from satellite and aircraft sensors during FIFE. J. Geophys. Res. 97:18785-18795.

Spanner, M., R. Wrigley, R. Pueschel, J. Livingston, and D. Colburn. 1990. Determination of atmospheric optical properties for the First ISLSCP Field Experiment (FIFE). J. 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. J. Geophys. Res. 97:18797-18814.