Georeferencing performance of THEOS satellite imagery

This paper reports on the application of a generic physical sensor orientation model for evaluation of the georeferencing performance of 2 m resolution imagery from the Thailand Earth Observation System (THEOS) satellite. Within the generic sensor orientation model, orbit and attitude data are employed to describe the satellite trajectory, which is further modelled by splines. The satellite orbit and sensor attitude errors are then compensated via sensor orientation adjustment using a modest number of ground control points (GCPs), resulting in improved georeferencing. The generic sensor model and the integration of the THEOS orientation parameters into the model are first described. The presence of errors in the satellite line-of-sight data, which result in imprecise sensor interior orientation are then discussed. Such errors can be effectively accounted for through modelling via a cubic polynomial, leading to sub-pixel georeferencing accuracy. An account is then given of an experimental evaluation of THEOS georeferencing conducted in a well-established testfield near Melbourne, Australia. The results demonstrate that sub-pixel 2D geopositioning accuracy is readily achievable with single THEOS images and within strips of up to three images, with as few as six GCPs to effect an orbit adjustment. However, accuracy decreases to near the 2-pixel level over a strip length of five images.