Correction to the Localization of NOAA AVHRR with DEM

Errors can often be found in the 51 longitude and latitude location information of each scan line in the NOAA AVHRR data which are preprocessed without taking the Digital Elevation Model (DEM) into consideration, and are dramatically huge at the points with high altitude and far from the nadir.The simulation indicates that the horizontal location bias will be increased with the increasing of the zenith angle.This bias caused by the location error can reach the kilometer order level and is mainly displayed in the longitude direction, with small weight of the latitude direction.It is necessary to correct this deviation.Even to the users who project first and then re-correct with the surface control-point, orientation correction can reduce the difficulty in re-correction and improve the orientation precise.A quick and simple method is developed by which localization information of 2048 satellite observation points in a scan line can be corrected with DEM and that of 51 original localization points in AVHRR L1B data. Firstly, latitudes and longitudes of 2048 satellite observation points are figured out using 51 original localization points' information by equidistance interpolation of one variable in an entire siding-to-siding block.Simultaneously the altitude of each point is looked up from DEM data.Secondly, one points is located exactly and the other is not revised.The horizontal location bias (i.e., spherical surface radian deviation) of which the former is relative to the latter can be achieved with DEM and the uncorrected point latitude and longitude.Thirdly, new localization information of the inaccurate point is calculated by dint of original localization points information and spherical surface radian deviation, and then the correction is finished.Because DEM influence to the location of several points at nadir is minimal, they can be considered as original points located exactly and then those on both sides are set as ones to be revised.Thereupon corrections can be carried out from nadir to verge step by step.The method can effectively decrease orientation errors in AVHRR data without the altitude information, which will contribute to the better use.