Georeferencing of UK DMC stereo-images without ground control points by exploiting geometric distortions

Abstract

This article 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, and the inter-imager offsets to determine the geolocation of individual pixels. The major step involved is the direct georeferencing of each pixel using satellite GPS and attitude sensor observations. The known separation between the sensors will allow us to determine the geolocations of all pixels that are taken at the same time using the same exterior orientation parameters. Traditional methods for georeferencing use GCPs, which are expensive and time-consuming tasks. Moreover, the traditional method is not suitable for a pushbroom imager because every scan line has a 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, causing deformation in the images. These effects have been modelled as a transformation matrix that describes the extent of deformation in the imagery, and is 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 is highly dependent on the accuracy of image offsets. The accuracy of image offsets is dependent on several factors, which include the image registration method, window size, along-track separation between the sensors, satellite attitude, and resolution of the sensors.