Automatic Adjustment of AVHRR Navigation

Abstract

An automatic adjustment method of the Advanced Very High-Resolution Radiometer (AVHRR) images navigation has been developed for operational use at the Centre de Météorologic Spatiale (CMS) in Lannion, France. Selected coastal landmarks are correlated with small windows of an actual AVHRR image using visible and near-infrared channels 1 and 2 for daytime images, and infrared channels 4 and 5 for nighttime images. The various stages of the method, generation of the reference landmarks, cloud discrimination, land-sea mask, and correlation between actual image and reference landmark are described. The CMS method has proven to be successful on 86% of the images of NOAA-11 day and night orbits from May to November 1990. The precision of the navigation after the adjustment is estimated to 0.8 pixel and 1.0 line when the adjustment is performed on the current orbit (58% of the cases), and to 1.0 pixel and 1.7 lines when the adjustment is performed on the preceding orbit (28% of the cams). The line and pixel errors corrected by the adjustment have the following characteristics: a constant pixel error of 3.0 pixels has been observed and is now applied to all the NOAA-11 images when the adjustment is not successful; the line error is variable with a mean value of ?0.8 line, and a rms error of 3.8 lines. This value of 3.8 lines is representative of the navigation error, which remains on the NOAA-11 images navigated without adjustment (14% of the cases).