The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
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out confirmed that a residual yaw of about 0.02 degrees could 
bring down the across track error for Fore. Further exercises 
and fine-tuning of residual biases are under progress. 
3.6 Development of new techniques 
A new development in in-flight calibration was resorted to 
exploit the capability of stereo sensors of Cartosat-1. 
Photogrammetric coplanarity condition (Mikhail et al. 2001) is 
used treating only two imaging sensors (stereo imaging in the 
same orbit) as attitude sensor to derive pseudo attitude 
parameters with minimum or no controls. This has given some 
promising results. Also, line based resection approach 
(Tommaselli et al. 1996) was developed and tested with 
Cartosat-1 to derive platform parameters making use of only 
image points as observations in the presence of other ancillary 
data. Absolute accuracy could be achieved with the help of a 
few controls. Preliminary results from these exercises are 
shown for comparison purpose in Table 2.0. 
Date Of Pass 
Camera 
Pre resection 
at system level 
(pixels) 
Coplanarity 
Model 
( pixels) 
No control 
used 
Line Based 
Approach 
(pixels) 
Two control 
points used 
RMS 
Scan 
RMS 
Pixel 
RMS 
Scan 
RMS 
Pixel 
RMS 
Scan 
RMS 
Pixel 
08 Jun.’05 
F 
29.86 
5.84 
6.58 
7.74 
6.67 
2.27 
A 
12.69 
3.21 
2.87 
4.31 
2.47 
1.81 
04 Nov.’05 
F 
29.13 
10.39 
4.28 
10.58 
9.35 
1.32 
A 
17.2 
26.77 
1.08 
25.43 
3.46 
1.02 
Table 2.0 Cartosat-1 results with different imaging models 
3.7 Results and discussions 
As described above, in-flight geometric calibration exercises 
has helped in re-estimation of some of the payload and 
platform parameters for use in Cartosat-1 DP s/w and SST s/w. 
The experiments conducted with SST s/w at various test bed 
regions using very precise GCPs establish that pre-resection 
results are within system level accuracy of 200m and post 
resection show model performance of SST better than 25m 
(Srinivasan et al. 2006). It is seen from SST results that large 
error occurring during earlier dates have come down 
considerably after accounting for various biases (Figure 4.0). 
Proper usage of payload alignment parameter, estimation of 
platform biases and adjustment of focal length for Cartosat-1 
had resulted in improvement of system level accuracy and 
standard deviation of data products thus meeting the Cartosat-1 
mission specifications. 
Tim* (mmm-yy) 
Figure 4.0 SST results showing improvement 
4. EXPERIMENTS WITH CARTOSAT-2 
As part of initial phase operations, in-flight geometric 
calibration exercises were taken up for Cartosat-2 to re 
establish the imaging geometry especially for step-stare 
viewing in order to improve the system level accuracy and 
deliver high-precision cartographic quality products. Various 
Cartosat-2 data sets along with a large number of test bed 
GCPs and TCPs from Cartosat-1 were used to re-estimate 
pseudo platform parameters. Report on the in-orbit geometric 
calibration exercises is given in the following subsection. 
4.1 Estimation of platform biases 
One of the activities identified as part of Cartosat-2 Post-launch 
Initial Phase Activities is the estimation of payload alignments 
with respect star sensor-1 (SSI) & star sensor-2(SS2). This 
activity demands precise identification of GCPs or TCPs in 
Cartosat-2 images. Using DP s/w utilities and precise imaging 
model, which in turn uses Cartosat-2 orbit, attitude and other 
payload, mission alignment parameters, image coordinates are 
estimated for the known ground coordinates of GCPs or TCPs. 
Then, a comparison was made between observed scan, pixel 
positions against estimated positions for all GCPs or TCPs. The 
differences observed in image positions are used to statistically 
derive various bias and alignment parameters as was done for 
Cartosat-1. 
4.2 Results and discussions 
It was observed that system level accuracy of Cartosat-2 data 
products during initial days were of the order of 1.3 km in 
along (scan) and around 1.1km in across (pixel) directions. All 
calculations carried out for this exercise was based on start 
sensor-1 knowledge. GCPs and/or TCPs were identified over 
various scenes from different test bed areas to assess the 
system level accuracy of the Cartosat-2 mission at model and 
product level. The overall initial system level accuracy at 
model points, taken up for analysis is given in Table 3. The 
data sets used include lm as well as 2.5m cases. Cartosat-1 in 
flight experiences were used for Cartosat-2 to derive the 
platform biases. As seen from the Table 3, it is observed that 
there is a consistency among various data sets in terms of along 
track and across track errors i.e around 1600 pixels and 1300