Remapped ATMS Radiance and its Validation for NPP Mission

Remapped ATMS Radiance and its Validation for NPP Mission

Chunming Wang¹, Degui Gu¹, Alex Foo¹, Giovanni De Amici¹

Fuzhong Weng², Ninghai Sun², Bi Li², Vince Leslie³

¹Northrop Grumman Corporation, One Space Park, Redondo Beach, CA 90278

² NOAA STAR, 5830 University Research Court Suit 2800, College Park, MD 20740

³Lincoln Laboratory, MIT, 244 Wood Street, Lexington, MA 02420-9108

Abstract

The Cross-track Infrared Microwave Sensor Suite (CrIMSS) launched on board the Suomi NPP satellite has the primary objective of measuring the Earth's atmospheric temperature and moisture profiles. The Advanced Technology Microwave Sounder (ATMS) and the Cross-track Infrared Sounder (CrIS) are the two key instruments of CrIMSS. While ATMS provides 96 brightness temperature measurements at 22 different microwave frequency channels during a cross-track scan, CrIS produces 30 measurements of atmospheric emission spectrum with over 1,300 channels in the infrared region. In order to effectively combine the data from both instruments to retrieve the atmospheric profiles, it is necessary to resample the native ATMS brightness temperature measurements for all its channels with different sizes of footprint to a specified common footprint that is coincident with the footprint of CrIS data. In particular, the current operational Suomi NPP algorithm generates 30 idealized composite brightness temperature measurements for every CrIS scan using up to 9 ATMS cross-track scan lines surrounding the CrIS scan line. For all 22 ATMS channels the footprints of these composite measurements overlap the footprints of the 30 CrIS Fields Of Regards (FOR). The resulting remapped ATMS brightness temperature is a key product for the Suomi-NPP mission in support of the generation of CrIMSS Environmental Data Records (EDR) and the direct data assimilation by NWP users. In this presentation, we review the main technical considerations for the algorithm for the production of the remapped ATMS brightness temperature. These include the incorporation of the pre-launch instrument characterization measurements, the relative alignment between ATMS and CrIS on the spacecraft, the synchronization of the scan mechanisms of the two instruments and, the practical geometric approximations used in the derivation of the resampling scheme. Even though the resampling approach is an adaptation of the widely known Backus-Gilbert method for generation of composite measurements, extensive pre-launch and post launch validation of the data product is essential. The fundamental challenge for validating the resample brightness temperatures is the lack of an actual microwave instrument with footprint corresponding to that of the composite brightness temperature. In this paper, we present our pre-launch and post-launch validation efforts for the resampled ATMS radiances. These efforts allow us to confidently conclude that the current remapped ATMS radiance provides unbiased representation of the microwave radiance over the effective composite footprint and that the intended noise reduction effects are achieved.