Global warping coefficients for improving ATSR co-registration

Abstract

Globally applicable warping coefficients for improving the co-registration between the forward and nadir views of the series of Along-Track Scanning Radiometer (ATSR) instruments are presented. The coefficients are derived from a polynomial-based warp, using a least squares fit on a set of automatically detected forward to nadir tie points. In-depth statistical analysis is presented here covering both an independent analysis of the warping coefficients using the Pyramidal-Gotcha algorithm and a global assessment using the Speeded Up Robust Features tie-pointing algorithm. This independent assessment shows that the co-registration between the nadir and forward views improves in all cases to pixel-level accuracy with geometric errors to, at worst, ±0.7 pixel. This global assessment analyses a worldwide distributed tie-point set to assess universal applicability. For Advanced ATSR and ATSR-1, the coefficients provide co-registration accuracies at the pixel level globally. The same is shown to be true for ATSR-2 prior to the gyroscope failure in January 2000.