1295 
STEREO EVALUATION OF CARTOSAT-1 DATA 
SUMMARY OF DLR RESULTS DURING CARTOSAT-1 SCIENTIFIC ASSESSMENT 
PROGRAM 
Manfred Lehner, Pablo d’Angelo, Rupert Müller, Peter Reinartz 
German Aerospace Center (DLR), Remote Sensing Technology Institute, Oberpfaffenhofen, 82234 Wessling, 
Germany 
{Manffed.Lehner, Pablo.Angelo, Rupert.Mueller, Peter.Reinartz}@dlr.de 
Commission I, SS-11 
KEY WORDS: CARTOSAT-1, Stereoscopic CCD scanner, Rational polynomial model, Matching, DSM generation, Orthoimage, 
Accuracy analysis 
ABSTRACT: 
The Remote Sensing Technology Institute (IMF) of the German Aerospace Center (DLR) has more than 20 years of history in 
developing spacebome stereo scanners and the corresponding stereo evaluation software systems. It takes part in the CARTOSAT-1 
Scientific Assessment Program (C-SAP) as a principal investigator for German (Southeast Bavaria) and Spanish (Catalonia) test 
sites and as a Co-I for a French test site (Mausanne-les-Alpilles). A rich variety of landscapes is present in these three test sites. In 
all cases ground truth in form of GCP (or orthoimages of high resolution) and DTM/DSM (digital terrain or surface models) of 
sufficient accuracy have been delivered by the principal investigators.Rational polynomial functions (RPC) are provided by the 
distributing Indian agency (Space Applications Centre (SAC) of ISRO, Ahmedabad) as a universal sensor model for each scene. The 
inherent absolute orientation accuracy of the RPC models in the CARTOSAT-1 stereo imagery used here turned out to be around 
100 m (normally). Thus, to exploit the high resolution of 2.5 m, RPC have to be corrected via the available ground truth. It is shown 
that the correction by an affine transformation is necessary in order to achieve sub-pixel accuracy in the stereo evaluation of full 
scenes. The remaining standard deviations of the residuals in image space during RPC correction are about 0.5-1 pixel in ground 
control points (GCP). Stereo evaluation is done by DLR processing software. Hierarchical intensity based matching and subsequent 
region growing are used to automatically derive a dense set of stereo tie points. An effective blunder reduction is based upon bi 
directional LSM, quasi-epipolar reprojection of the tie points, and control of residuals in stereo forward intersection. Shifts between 
aft/fore orthoimages are found to be in sub-pixel range. DSM accuracy assessment is done via the statistics of height differences 
compiled by the forward intersection software. This is sufficient if accurate GCP for RPC correction are available. For direct 
comparison of the generated DSM with the reference DTM/DSM a 3D shift is estimated via least squares adjustment and mean and 
standard deviations of the DTM/DSM differences after shifting are provided. In summary, standard deviations of 2-4 m are achieved. 
1. INTRODUCTION 
1.1 DLR participation in C-SAP 
DLR is engaged in 3-line stereo scanner development and data 
evaluation since 1980 when ISRO offered to fly such a DLR 
camera on SROSS-I satellite to be launched by Indian ASLV 
rocket in 1988. The camera has been built and the German 
photogrammetric community and also ISRO/SAC could exploit 
airborne 3-line scanner imagery of a MEOSS camera model 
from 1986 onwards (Lehner and Gill 1992, Heipke et al. 1996). 
DLR in subsequent years concentrated on the German 3-line 
scanner MOMS-02 which was successfully flown as MOMS- 
02/D2 instrument on space shuttle mission D2 in 1993 and as 
MOMS-2P on the Russian space station Mir from 1996 till 1999. 
MOMS mission brought the development of a MOMS stereo 
work station at DLR through cooperation of DLR with several 
German universities (Seige et al. 1998, Komus et al. 2000). 
The next along-track stereo scanner in space investigated at 
DLR/MF was the HRS instrument on SPOT-5 (launched in 
May 2002). DLR took part as a PI in the HRS scientific 
assessment program in 2003-2004 (Reinartz et al. 2006). 
In the following years the DLR stereo evaluation and ortho 
projection software which was up to then based on rigorous 
modelling only was supplemented by software for RPC based 
ortho-projection, forward intersection, RPC correction, and 
quasi-epipolar reprojection of stereo pairs. This was necessary 
for the orthoimage and DSM generation from the new high 
resolution monoscopic and stereo imagery of IKONOS-2 and 
QuickBird satellites (Lehner et al. 2005). 
In May 2005 India launched its IRS-P5 satellite with 
CARTOSAT-1 instrument which is a dual-optics 2-line along- 
track stereoscopic pushbroom scanner with the very interesting 
resolution of 2.5 m which is adequate for many 3D mapping 
tasks. The operational use of the data is described in (Srivastava 
et al. 2007). After approximately one year of operation for the 
3D mapping of India, from June 2006 onwards data were made 
available to international investigators in the frame of the 
CARTOSAT-1 Scientific Assessment Program (C-SAP) by the 
Space Applications Centre (SAC, Ahmedabad) of the Indian 
Space Research Organisation (ISRO). Intermediate results have 
been presented by PI and Co-I during ISPRS TC IV symposium 
in Goa (India) in September 2006 and during ISPRS Inter- 
Commission workshop in Hanover (Germany) in May/June 
2007.