The navigation processing within the Level-0-to-1A conversion has been improved, to reduce the seasonal variations in spacecraft yaw error. The most significant improvement will be seen in the Southern hemisphere during the Winter and early Spring. This was accomplished by incorporating additional seasonal corrections into the horizon angle model which is used in the spacecraft attitude determination, based on analysis of the navigation errors from Reprocessing #3.
An example of the improvement is shown in the images below, which were generated from an HRPT file collected at the Pretoria station on March 4, 2001. The first image shows the coastline registration with the original navigation processing. The second shows the result of the new navigation processing. The improvement is clearly visible, although some misregistration can still be seen.
