Operational AVHRR navigation results

A navigation method that combine a precise image deformation model and an automatic adjustment on coastal landmarks is operationally used at the CMS on AVHRR imagery. This paper presents the principles of the method, the error sources and a detailed analysis of the results obtained in 1996-1997 with NOAA-14 and NOAA-12 images. Both ARGOS or TBUS orbital elements were used and yield similar results. The AVHRR image navigation without any landmark adjustment, is 3.9 km for NOAA-14 and 8.7 km for NOAA-12. The navigation error before ANA, which assumes a constant attitude error, is similar for NOAA-14 3.5 km, but is greatly reduced for NOAA-12, 2.2 km. The NOAA-14 error is mainly due to clock error temporal variations, poorly known in real time, whereas the NOAA-12 error results from attitude errors of 5 mrad roll and 1.5 mrad yaw. The AVHRR image navigation error after landmark adjustment is 1.7 km. The landmark adjustment gives better performances on NOAA-14 images (with 60.1% success on the current orbit) than on NOAA-12 images (51.7% success); these values are increased to 88.9% for NOAA-14 and 84.0% for NOAA-12 when using the attitude estimated on the preceeding orbit.