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IMPROVEMENTS IN CARTOSAT-1 STEREO ORTHOKIT DATA PRODUCTS SINCE 
LAUNCHING ISPRS-ISRO CARTOSAT-1 SCIENTIFIC ASSESSMENT PROGRAMME 
R. Nandakumar*, Shilpa Prakash, B. Kartikeyan, MPT Chamy, Sanjay Singh, TP Srinivasan, Amitabh, 
B. Gopala Krishna, Santanu Chowdhury & PK Srivastava 
Signal & Image Processing Area, Space Applications Centre, 
Indian Space Research Organisation, Department of Space, Ahmedabad - 380 015, India - 
(nandakumar, pshilpa, bkartik, mptchamy, sks, tps, amitabh, bgk, santanu, pradeep)@sac.isro.gov.in 
Commissioni, SS-11 
KEYWORDS: Cartosat-1, DEM generation, Rational polynomial coefficients, MTF improvement, Point spread function, Image de- 
convolution 
ABSTRACT: 
Along-track stereo data from the two panchromatic CCD sensors Fore and Aft onboard Cartosat-1 satellite are being operationally 
received and data products generated after the satellite 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 Phase-I 
investigations carried out by different teams have yielded useful insights for improving the Cartosat-1 stereo orthokit data products, 
both radiometrically as well as geometrically. Radiometrically, MTF (modulation transfer function) of the images acquired by both 
Fore and Aft sensors onboard Cartosat-1 have been enhanced considerably based on pre-launch ground calibration data. 
Geometrically, the RPCs (rational polynomial coefficients), which provide the image-to-ground geometric relationship, for the 
images acquired from the Fore and Aft sensors, have been modified to rectify the anomaly of occasional zero crossovers in the 
denominators; as well as to modify the longitude convention used in the data products to -180 to +180 degrees instead of 0 to 360 
degrees. This Paper presents the details of both these radiometric and geometric improvements along with a few sample results. 
1. INTRODUCTION 
This Paper discusses the radiometric and geometric 
improvements incorporated to the Cartosat-1 stereo orthokit 
data products along with a few sample results. Radiometrically, 
the image modulation transfer functions (MTFs) have been 
improved for both the Fore and Aft panchromatic sensors 
onboard Cartosat-1. Geometrically, certain anomalies reported 
in the rational polynomial coefficients for the zero-cross-over 
cases have been rectified and a convention mismatch in 
representing longitude values has been set right. 
1.1 CARTOSAT-1 Mission and Fore & Aft Instruments: 
Cartosat-1, one of the optical Indian remote sensing satellites, 
was launched on May 5, 2005 by ISRO from the Satish Dhawan 
Space Centre at Sriharikota. It has two identical and 
independent PAN sensors, Fore and Aft, having a resolution of 
2.5 m acquiring images in stereo mode for the production of 
digital terrain models as well as in wide-swath mode for the 
production of mono image mosaics. 
The Fore and Aft cameras are inclined fore-ward and aft-ward 
by + 26° and - 5° along the ground track, giving a base-to-height 
ratio of 0.62. These instruments operate in the panchromatic 
band with 10-bit radiometry and a swath of 27.5 km each. 
During imaging, the spacecraft is maneuvered continuously so 
as to acquire either stereo or wide-swath images. This 
maneuvering could be done throughout the length of the pass 
for a given ground station or for any desired portion thereof. 
The stereo imaging provisions of the spacecraft include options 
to be tilted either in the pitch direction to acquire additional 
stereo images with - 26° and + 5° or symmetrically with ± 15.5° 
or in roll direction to cover specific areas with a reduced revisit 
period. More details on the Cartosat-1 mission and the sensors 
could be seen in Srivastava et al., 2006. 
1.2 C-SAP: 
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 data were provided by ISRO. The 
combined data sets were provided to respective investigators of 
each test site in two phases, first in May-June 2006 for the 
Commission-IV Goa Symposium held in September 2006 in 
India and for the Inter-Commission Hannover Workshop in 
Germany held in May, 2007; and secondly for the Beijing 
Congress in China being held in July 2008, subsequent to the 
Goa Symposium. See Nandakumar et al., 2006 for more details 
on C-SAP.