Geometric and radiometric investigations of Cartosat-1 data

The Institute of Geodesy and Photogrammetry (IGP) is participating in the Cartosat-1 evaluation program, a common initiative of ISRO (India) and ISPRS. Within this program various test sites with reference data have been established and Cartosat-1 images have been acquired over these sites. Here, we will report about our investigations at the Rome and Mausanne test sites. First, we report on radiometric problems encountered with the images and preprocessing for their improvement. These include artefacts, unfocussing in the forward channel and scale differences to aft, jitter at horizontal edges, interlacing errors and pattern noise. We show examples and also preprocessing methods that can be employed in order to improve image quality, with aim especially to automatically generate a DSM with less blunders (due to noise and artefacts) and more match points. Then, we report on sensor modelling and the 3D point positioning accuracy that can be achieved, as well as various problems encountered with the Rational Polynomial Coefficients (RPCs). The orientation results were produced using various options regarding image preprocessing, sensor model, number and distribution of GCPs and GCP image mensuration methods. The best results led to a planimetric and height accuracy (RMSE) of about 1.3 m. The absolute geolocation accuracy varies greatly from dataset to dataset and can be worse than a few thousand meters, making Cartosat-1 unsuitable for generation of global mapping products without use of GCPs. Finally, we present the results of automatic DSM generation using our own Sat-PP program package. Various DSMs were generated with 10m grid spacing. The results were checked both visually and were compared using the provided reference data. In the best case, the achieved accuracy is about 2.7 m without any manual editing and in spite of 3-year difference between matching and reference DSM. In spite of several aspects that could and should be improved, Cartosat-1 is a useful sensor for mapping and especially generation of DSMs. * Corresponding author.