RECENT ADVANCES IN CARTOSAT-1 DATA PROCESSING

With the launch of Indian Remote Sensing satellite Cartosat-1, an along-track stereo mission, new possibilities for operational availability of high resolution stereo imagery from space for user communities of remote sensing and cartography have emerged. The high-resolution stereo data beamed from twin cameras onboard Cartosat-1 mission facilitates topographic mapping up to 1:25,000 scale. The primary advantage of Cartosat-1 mission is seen in generation of DEM and production of Orthoimage in an operational setup. This also facilitates 3D terrain visualization for very large tracts of land. Stereo Strip Triangulation (SST) is a software system developed and perfected at Space Applications Centre of Indian Space Research Organisation for operational generation of secondary control and appropriate DEM for subsequent use in generation of Orthoimages. This system is in use for almost two years at Data Products generation centre at Hyderabad, India and has generated a wealth of data for use in topographic mapping. An initiative to generate a database of seamless & homogeneous DEM & associated Ortho-image Tiles at country level has been undertaken by ISRO. This data set has been named CartoDEM. The Cartosat-1 data processing team has completed design and testing of software for generation of CartoDEM. Currently this software system is in final stage of evaluation and operationalisation to maximally utilise Cartosat-1 sensors’ capabilities. A data dissemination software system is currently under development. As part of large scale evaluation exercises to finalise specifications of CartoDEM, it is established that with the 2.5 m ground resolution, a base to height ratio of 0.62, and with capability to register conjugate points in the stereo pair to a sub-pixel level, digital elevation models could be generated in 0.3 arc seconds interval with a height accuracy of 3-4 m over tracts of undulating land mass up to 15,000 square km. with use of 10-20 ground control points. Cartosat-1 Data processing and evaluation team regularly monitors the radiometric quality of images. As part of radiometric characterisation of sensors the team computed Point Spread Function (PSF) for the two cameras of Cartosat-1. Special filters are then devised to attempt to use PSF to improve radiometric quality of images. Initial results from these exercises show good promise and image restoration based on PSFs is in the process of detailed evaluation and operationalisation. This paper presents summary of activities and exercises related to (i) Stereo Strip Triangulation, (ii) CartoDEM, (iii) Image quality improvement using Point Spread Function (PSF) based image restoration and (iv) Block adjustment exercises using COTS software package. Also reported are the results of post-launch experiments, study and evaluation of DEM vis-a-vis Orthoimages from Cartosat-1.