Geo referencing of Images by Exploiting Geometric Distortions in Stereo Images of UK DMC

Abstract

This research describes a new method for the georeferencing of UK DMC imagery that does not require ground control points (GCPs). The proposed method utilizes satellite ancillary data, a digital elevation model (DEM) and the inter-image offsets to determii1e the geo-location of individual pixels. The major steps involved are direct georeferencing of each pixel using satellite GPS and attitude sensor observations and then tune or refine these initial estimates iteratively by utilizing the data from a DEM. The known separation between the sensors allows us to determine the geo-locations of all pixels that are taken at the same time using the same exterior orientation parameters. Traditional methods for georeferencing use GCPs which is expensive and time taking task. Also traditional method is not suitable for pushbroom imager because every scan line has different set of exterior orientation parameters. Therefore, we pro­pose a direct georeferencing approach without GCPs. The major source of error in direct georeferencing is the error in attitude measurements. The reason for this error is considered to be the thermo-elastic effects on the satellite, which affect the sensors positioning and causes deformation in the images. These effects have been modeled as a transformation matrix which describes the extent of deformation in the imagery, and estimated by exploiting the geometric distortions in stereo Earth images. For this purpose, a mathematical model has been developed to demonstrate how inter-image offsets have been introduced into the imagery and affected by thermal deformation. The mathematical model is based on the sensor configuration of UK DMC satellites. The model has been further inverted to extract the thermal defor­mation at a given row and column offset. The thermal deformation matrix has been found to mitigate the pointing error up to 1 Km. The accuracy of the thermal deformation estimates are highly dependent on the accuracy of image offsets. The accuracy of huage offsets is dependent on several factors which include image registration method, window size, along track separation between the sensors, satellite attitude and resolution of the sensors.