Comparison of measurements from satellite radiation budget instruments (Invited Presentation)

Successive radiometers have been flown on spacecraft for measurement of the radiation budget of the Earth and to date have provided data sets which overlap in time over a 25-year period. Together these data sets cover two cycles of a decadal oscillation and are useful for climate research. However, although these instruments were all calibrated with great care, inevitably there are differences between the instruments. Also, the instruments change while in orbit due to degradation of optical elements and changes of the detectors. A number of studies have compared measurements between pairs of radiometers in order to establish these differences. In this paper we compile these results in order to demonstrate the traceability of calibration of satellite radiation budget instruments over these two decades. In this compilation the differences can be computed for any two instruments listed. The instruments considered here include the ERBE scanning and non-scanning radiometers, ScaRaB I, CERES aboard the TRMM, Terra and Aqua spacecraft, and GERB. One underlying assumption of this paper is that each instrument is calibrated both on the ground and in orbit without regard to the others. Comparison of higher level data products, e.g. gridded fluxes, introduce questions such as the variation of flux from one time to another, solar lighting conditions, etc. For this reason, direct comparison of measurements which are coincident in time and space is preferable. These measurements are compared and differences noted so that users of multiple data sets can take into account these differences in their work. No attempt is made here to adjust the data sets to form a self-consistent long-term data set.