Solar calibration results from two earth radiation budget experiment nonscanner instruments

Abstract

Earth radiation budget experiment (ERBE) nonscanner instruments are operating on both the National Aeronautics and Space Administration's earth radiation budget satellite (ERBS) and the National Oceanic and Atmospheric Administration's NOAA-9 spacecraft. These instruments are designed to make highly accurate broadband measurements of the earth's energy budget on spatial scales ranging from 10° earth central angle to global over temporal scales ranging from 30 days to annual averages. As part of the in-flight calibration of these instruments, the four nominally earth viewing radiometric channels are periodically repositioned for solar viewing. At the same time, a fifth (solar monitor) channel is activated. These solar calibrations were performed weekly during the first two months of operation of each spacecraft and biweekly thereafter. Results from the first few months of operation show an extremely consistent set of solar measurements. Each of the ten channels has a precision of approximately ±0.1% and a measurement uncertainty estimated to be ±0.2%. The ERBS and NOAA-9 solar monitors have yielded provisional solar irradiance values of 1364.3 and 1363.5, agreement to within 0.06%. A description of the solar calibration process is presented along with engineering results from each of the ten radiometric channels over the first few months of operation. The solar calibration data reduction process is also discussed.