Advanced Technology Microwave Sounder (ATMS) Geolocation Analysis

Geo-location pointing knowledge and accuracy ensure that the characteristics of a measured scene are well understood and can be documented. As part of the Advanced Technology Microwave Sounder (ATMS) calibration/validation effort, a geolocation pointing analysis was conducted to determine the pointing accuracy of the ATMS fields of view. Measured brightness temperatures were used to detect land to sea transitions. These were compared to “Truth” shoreline positions provided by the Global Self-consistent, Hierarchical, High-resolution Shoreline (GSHHS) database. Two different analysis methods were used to achieve sub-pixel (footprint) resolution accuracy. The first method used a cubic polynomial fit to four sequential sensor measurement pixels that crossed the land sea boundary. The shoreline position was then calculated as the inflection point of the polynomial. The second method fit synthetic scenes, created from the land/sea fraction in each footprint, to the brightness temperature scenes observed by ATMS. Both methods achieved good results and will be compared in this paper. From the total of 22 ATMS channels, channels 1, 2, 3, 16, & 17 were chosen to represent the five different bands. Channels 1, 2, 3, and 16 are considered window channels so can readily be used to detect coastlines. Channel 17 is sensitive to water vapor but, under dry conditions the atmosphere is sufficiently transparent to detect coastlines. Coastal crossing errors were calculated for a number of different earth locations. Results show that dry desert location such as the Red Sea generally worked the best. The observed geolocation errors were then related to the roll, pitch, and yaw angular deviations from ideal beam alignment. This paper describes the methods used to derive geo-location accuracy, provides summary results and gives specific examples scenes that were used to derive the results.