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

A joint campaign was held at Lunar Lake Playa, Nevada (USA) in June 1996 to evaluate the accuracy of reflectance-based, vicarious calibrations of Eart h Observing Systems (EOS), Four groups participated in the campaign and mad e independent measurements of surface reflectance and atmospheric transmitt ance on five different days. Each group predicted top-of-the-atmosphere rad iance for several bands in the 400 nm to 2500 nm spectral range. Analysis o f the data showed differences of the order of 5% to 10% throughout the spec tral region under study. Further study revealed that the major sources of d iscrepancy are differences in procedures and assumptions in finding the ref lectance of field references used to determine the surface reflectance of t he test site. Differences caused by varying radiative transfer codes and ae rosol assumptions were found to be a relatively small error source, owing t o the high reflectance and low turbidity of the test site. Differences in t he solar irradiance values used by separate groups were found to be signifi cant, but can be overcome by agreeing on a standard solar irradiance data s et. The results from this campaign were used to plan a follow-up campaign i n June 1997 that included developing a set of laboratory measurements to ch aracterize the field radiometers which measure surface reflectance, and obt aining a consistent set of reference-panel reflectance factors. The expecta tion is that disagreement in absolute radiances at the top of the atmospher e generated by these field methods will be reduced to less than 3% if furth er cooperative work between groups is carried out to develop approaches whi ch will account better for reference panel calibration, the consistent use of atmospheric characterization and radiative transfer codes.