Geolocation of AMSR-E Data

The process of determining the geographic latitude and longitude (lat/lon) of the center point of the footprint is called geolocation, which is currently suboptimal for the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) Level 1 data provided by Japan Aerospace Exploration Agency (JAXA). Here, we present a study for improving the geolocation. The viewing angles (the nadir angle and the scan angle) that define the boresight direction of the instrument are optimized, and new lat/lon coordinates are calculated. The optimization method is based on minimizing the differences between ascending and descending swaths. The results of the calculated viewing angles here have an overall standard deviation of 0.005 degrees, which is 170 m on ground for the nadir angle and 70 m for the scan angle. The residual geolocation error ranges between 425 m (89 GHz) and 1425 m (6 GHz). The averaged repositioning between JAXA and our geolocation ranges between 3.5 and 7 km, i.e., in the order of one footprint size at 89 GHz. A comparison with a similar study, performed by Wentz et al., shows a good agreement in the viewing angles; the root mean square of the differences is 0.0083 degrees (approximate to 283 m) for the nadir angle and 0.0132 degrees (approximate to 191 m) for the scan angle.