Results of the 1996 Earth Observing System vicarious calibration joint campaign at Lunar Lake Playa, Nevada (USA)

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Abstract
A joint campaign was held at Lunar Lake Playa, Nevada (USA) in June 1996 to evaluate the accuracy of reflectance-based, vicarious calibrations of Earth Observing Systems (EOS). Four groups participated in the campaign and made independent measurements of surface reflectance and atmospheric transmittance on five different days. Each group predicted top-of-the-atmosphere radiance for several bands in the 400 nm to 2500 nm spectral range. Analysis of the data showed differences of the order of 5% to 10% throughout the spectral region under study. Further study revealed that the major sources of discrepancy are differences in procedures and assumptions in finding the reflectance of field references used to determine the surface reflectance of the test site. Differences caused by varying radiative transfer codes and aerosol assumptions were found to be a relatively small error source, owing to the high reflectance and low turbidity of the test site. Differences in the solar irradiance values used by separate groups were found to be significant, but can be overcome by agreeing on a standard solar irradiance data set. The results from this campaign were used to plan a follow-up campaign in June 1997 that included developing a set of laboratory measurements to characterize the field radiometers which measure surface reflectance, and obtaining a consistent set of reference-panel reflectance factors. The expectation is that disagreement in absolute radiances at the top of the atmosphere generated by these field methods will be reduced to less than 3% if further cooperative work between groups is carried out to develop approaches which will account better for reference panel calibration, the consistent use of atmospheric characterization and radiative transfer codes.