Advanced studies in strip pair processing of Cartosat‐1 data

Abstract

AbstractWith the launch of the Indian remote sensing satellite Cartosat‐1, an along‐track stereoscopic imaging mission of the Indian Space Research Organisation (ISRO), new possibilities for operational availability of high‐resolution stereo‐imagery from space for the remote sensing and cartography user communities have emerged. The high‐resolution stereo data beamed from twin cameras on board the Cartosat‐1 mission facilitates topographic mapping up to 1:25 000 scale. The primary advantage of the Cartosat‐1 mission is seen in the generation of digital elevation models (DEMs) and the production of ortho‐images in an operational set‐up. This also facilitates 3D terrain visualisation for very large tracts of land. Stereo Strip Triangulation (SST) is a software system developed and perfected at the Space Applications Centre of ISRO for operational generation of secondary control and appropriate DEMs for subsequent use in the generation of ortho‐images. This system has been in use for almost 2 years at the National Remote Sensing Agency in Hyderabad, India, and has generated a wealth of data for use in topographic mapping. An initiative to generate a database of seamless, homogeneous DEMs and 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 the design and testing of software for the generation of the CartoDEM. This software system has undergone detailed evaluation and currently is in the final stage of development of the operational procedures required to make maximum use of the capabilities of the Cartosat‐1 sensors. A data dissemination software system is currently under development. As part of the large‐scale evaluation exercises to finalise the 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 stereopair to sub‐pixel level, DEMs can be generated at 0·3 arc second intervals, with a height accuracy of 3 to 4 m, over tracts of undulating land mass up to 15 000 km2 with the use of 10 to 20 ground control points. The Cartosat‐1 data processing and evaluation team regularly monitors the radiometric quality of images. As part of the radiometric characterisation of sensors, the team computed point spread functions (PSFs) for the two cameras of Cartosat‐1. Special filters based on the PSFs then work to improve the radiometric quality of the images. Initial results from these exercises show good promise in image restoration based on PSFs for Cartosat‐1. This paper presents a summary of activities and exercises related to (i) Stereo Strip Triangulation, (ii) CartoDEM, (iii) image quality improvement using the PSF‐based image restoration and (iv) block adjustment exercises using a COTS software package. Also reported are the results of post‐launch experiments, study and evaluation of DEMs vis‐à‐vis ortho‐images from Cartosat‐1.