Absolute and Relative Validation of the Geolocation of the ATMS SDR Data

Absolute and Relative Validation of the Geolocation of the ATMS SDR Data

Chunming Wang, Degui Gu, Alex Foo

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

Abstract

The Advanced Technology Microwave Sounder (ATMS) on board the Suomi NPP satellite produces cross-track measurements of microwave radiances in 22 frequency channels. The ATMS data is essential for the retrieval of the atmospheric temperature and moisture vertical profiles. While the ATMS measurements alone could be used to produce the atmosphere profiles, the combination with infrared measurements from the Cross-track Infrared Sounder (CrIS) would substantially increase the vertical resolution and accuracy of the retrieved profiles. The need for co-registering ATMS and CrIS data, as well as the potential use of ATMS measurements for climatologic applications, require highly accurate geolocation of the ATMS measurements.  Technical challenges for the validation of the geolocation of the ATMS data include the large size of the instrument footprint and unavailability of high resolution reference measurement in the microwave frequency range. Following the launch of Suomi NPP satellite, we have developed an approach for using the highly accurate geolocation of the Visible Infrared Imager Radiometer Suite (VIIRS) emissive band measurements to conduct a relative validation of the geolocation of the ATMS data. Our approach makes use of the high brightness temperature contrast between land and ocean surface areas in a coastal scene to estimate the relative geolocation error between ATMS and VIIRS. In particular, high contrast scenes over coastal regions without cloud intrusion were identified using VIIRS data. The ATMS data over these selected scenes are isolated. Measurements of mismatch between the infrared brightness temperature of the VIIRS data and that of microwave data from ATMS are analyzed. Several measurements of the mismatch are evaluated during our investigation for their sensitivity to the geolocation errors and for their robustness to residual cloud contaminations of the scenes. These measurements include cross correlation between the microwave brightness temperatures and the averaged high resolution infrared brightness temperatures over the ATMS footprints, as well as the relative location differences of land and ocean edges in microwave and infrared scenes. Our analysis shows that the sensitivity and robustness of these measurements can be significantly improved when narrow thresholds for separating land and ocean radiances are first applied to the infrared measurements. Since a “flattened” infrared scene resembles a land mask, we could use an actual land mask to perform the identical analysis. In fact, when a land mask is used in lieu of the VIIRS data, we obtained an absolute validation of the geolocation for the ATMS data. Our analyses show that a geolocation bias of over 3 km exists for the ATMS data relative to the VIIRS measurements. In this presentation, we shall provide detailed description of the technical approach for the characterization of geolocation error and the analysis results using VIIRS and ATMS data from the Suomi NPP mission.