Toward an integrated system for the calibration/validation of multisensor radiances from operational satellites

The quality of satellite radiances is essential for direct radiance assimilation in numerical weather prediction, for retrievals of various geophysical parameters, and for climate trending studies. It is also a measure of the success of the engineering and science efforts of our operational satellite program. However, past efforts in postlaunch calibration/validation took a piecemeal approach, focusing on onboard calibration, with much less attention paid to the quality of radiance data of earth observations. Many instrument related artifacts were left to the users to discover, and evaluate the impacts. The lack of on-orbit calibration standard and methodology for radiance verification also aggravated the problem. We believe that in order to meet the challenge of the increasing demand for better satellite data quality, an integrated approach for calibration/validation should be used. Specifically, an integrated system that incorporates prelaunch, postlaunch onboard and vicarious, and longterm monitoring, as well as forward calculation of radiances is needed. The core components of the system includes 1). Comparison of prelaunch and postlaunch instrument performance; 2). near-real time monitoring of instrument performance parameters; 3). Intersatellite calibration of radiances using the simultaneous nadir overpass (SNO) /simultaneous conical overpass (SCO) method. 4); Forward calculation of radiances produced by the instruments using model atmosphere and in situ observations. The SNO/SCO and forward calculations serve as a feedback for the verification of onboard calibration; 5). Spatially collocated and spectrally convolved intra-satellite multisensor analysis; 6). Vicarious calibration at specific sites; 7). Other methodologies for moon calibration and geolocation evaluation; 8). An integrated website that provides frequent update of the above. This integrated system will bring together all operational satellite radiometers and make the radiances highly traceable among a constellation of global satellites in both polar and geostationary orbits. In this paper we introduce our efforts and progress in developing this integrated system and plans in supporting the calibration/validation and longterm monitoring of POES/NPOESS radiometers. The role of this integrated system in support of the GEOSS is also discussed.