SYNTHESIS OF INVESTIGATIONS UNDER ISPRS-ISRO CARTOSAT-1 SCIENTIFIC ASSESSMENT PROGRAMME PRIMARILY FOR DSM GENERATION

摘要

Cartosat-1 with two identical optical sensors Fore & Aft operating in panchromatic band to operationally acquire along-track stereo images (or wide-swath mono images) was launched by the Indian Space Research Organisation (ISRO) from the Satish Dhawan Space Centre, Sriharikota on May 05, 2005. ISPRS-ISRO Cartosat-1 Scientific Assessment Programme (C-SAP) was initiated with an announcement of opportunity on January 13, 2006, through an e-mail and a web-page announcement in Commission-IV website for evaluating the mapping potential of Cartosat-1 stereo data. A number of test sites and investigators spread across the globe were selected for this Programme by an international evaluation team. Principal Investigators provided reference data sets over the test sites for which Cartosat-1 stereo orthokit data products were provided by ISRO. The results of these investigations by not less than 14 independent teams on at most 11 test sites using a variety of in-house-generated and commercial photogrammetric processing software, with data acquired by Cartosat-1 during different seasons of the year have been presented in (a) Commission-IV Symposium at Goa in Sep. 2006, (b) Inter-Commission Workshop held at Hannover in 2007 and (c) currently at Beijing in July 2008. While these investigations cover (1) stereo triangulations with one or two overlapping stereo pairs for sensor orientation and 3D-geo-positioning, (2) stereo image matching, space intersection and interpolation to generate a regular grid of Digital Surface Model (DSM), (3) orthoimage generation using either of the Fore or Aft sensor data sets, (4) feature extraction & (5) topographic mapping; along with evaluations at each step with reference data sets of higher (or comparable) quality, this Paper is an attempt to synthesise all the results of these investigations to draw conclusions on the overall capabilities of Cartosat-1, with primary emphasis placed on DSM generation. The conclusions include: Employing a few externally measured and precisely transferred ground control points, Cartosat-1 stereo pairs could be successfully used (1) to generate DSMs with 5 m grid posting in rolling plains; (2) to generate DSMs with 10 m grid posting in all other types of terrains (including hilly) with an accuracy of 0.5 pixel in planimetry and 1-2 pixels (1σ) in height; (3) to generate orthoimages with sub-pixel accuracy; and (4) to generate topographic base maps in 1:10,000 scale. The capability of Cartosat-1 image data sets are superior to ALOS-PRISM, SPOT-HRS, IKONOS or QuickBird particularly to generate DSMs, in the light of their 10-bit radiometry with a wider panchromatic band, optimal stereo angles for better stereo image matching and operational along-track stereo acquisition.