Broadband Solar Irradiances Measured on Fixed and Stabilized Platforms

Over the past 40 years radiative transfer models have consistently under-predicted the amount of solar absorption by clouds. Estimates of the size of this discrepancy at the beginning of its discovery were ~10 W/m^2, but in 1995 jumped to 40-100 W/m^2, which ARESE I was formed to resolve. ARESE I being inconclusive, ARESE II was conducted and further studies brought the estimates back to ~10 W/m^2. Part of the problem lies with the difficulty of obtaining accurate measurements of the absorbed solar insolation as well as constructing models that represent real atmospheric conditions. So after ARESE II was completed an experiment was performed to test the effectiveness of a new technique-the stabilized platform. A pyranomter mounted on a stabilized platform, which kept the instrument on board the Proteus aircraft in the earth's horizontal plane, was used to measure the solar flux. Another pyranomter, mounted on a standard fixed platform, was also aboard the Proteus. Since the observations of the fixed platform have to be corrected for the movements and deformation of the aircraft, there is an additional source of uncertainty. Thus the aim of this study was to determine the flux and absorption uncertainties observed from the fixed and stabilized platforms. The fixed platform flux uncertainties, at 4.4-14.8 W/m^2, were ~1.8 times those of the stabilized platform which were 3.8-8.2 W/m^2. However, the fixed flux uncertainties were not so great as to invalidate the pre-ARESE I and ARESE I studies