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ISPRS Journal of Photogrammetry Remote Sensing 54 1999 289–297
Pass processing of IRS-1Cr1D PAN subscene blocks
1
P.V. Radhadevi
AdÕanced Data Processing Research Institute, Department of Space, 203 Akbar Road, Tarbund, ManoÕikasnagar Post, Secunderabad 500 009, India
Received 30 September 1998; accepted 29 April 1999
Abstract
This paper describes a method for pass processing of IRS-1Cr1D imagery acquired by the three CCD arrays of the Ž
. panchromatic PAN camera. It is based on the fact that during a single pass, the image data stream from the three CCD
arrays of the PAN camera can be adjusted together as a single image, exploiting the knowledge of the internal geometry and the angular relationships between the CCD arrays. The geometry of this extended image can be rectified with a single
Ž .
ground control point GCP . A full PAN scene consists of nine subscenes, each with a dimension of 23.5 km = 23.5 km. The Ž
. method is not restricted in the number of continuous full scenes in the same pass that can be adjusted. The scale variations
between the images from the three detectors are corrected by computing the relative focal lengths of detectors 1 and 3 with respect to detector 2. Two tests were conducted to verify the accuracy of the adjustment procedure. Average root-mean-square
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RMS errors of 10.5 m in the latitude direction and 11.3 m in the longitude direction were obtained with a single surveyed GCP and a set of survey points used as checkpoints. The results of the tests show that the adjustment of full PAN
scenes, as proposed in this paper, is an effective means of reducing the number of GCPs required for precise determination of ground coordinates. q 1999 Elsevier Science B.V. All rights reserved.
Keywords: IRS-1Cr1D PAN; sensor modelling; block adjustment; rectification; ground control points; planimetric accuracy analysis
1. Introduction
High resolution and off-nadir viewing capability are the most innovative features of the IRS-1C PAN
camera. Details of the IRS-1C spacecraft and its Ž
. camera systems are given by George et al. 1996
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and Kasturirangan et al. 1996 . The PAN camera has a spatial resolution of 5.8 m and consists of three
CCD arrays, each having 4096 active sensor ele- ments. This camera can be steered up to 268
E-mail: pv _
radhadevihotmail.com
1
Revised version of a paper presented at the ISPRS Com. I Symposium, Feb. 25–27, 1998, Bangalore, India.
across-track which, in turn, increases the revisit ca- pability to five days. The nominal inter-pixel dis-
tance in the image plane is 7 mm. Each multispectral LISS-III scene can accommodate four full PAN
scenes designated as A, B, C and D. An overlap of approximately 1 km exists in the path direction
between A and C, and B and D. During a single pass, either A and C or B and D are acquired. We
have developed a method for orienting the continu-
Ž ous image data streams A and C of one pathrrow
and subsequent quadrants A and C of the next row of the same path, i.e., four full PAN scenes along the
. same path and pass with a single ground control
Ž .
point GCP . A PAN full scene consists of nine subscenes, each of dimensions 23.5 km = 23.5 km.
0924-2716r99r - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž
. PII: S 0 9 2 4 - 2 7 1 6 9 9 0 0 0 2 1 - 0
IRS-1C imagery is acquired in a continuous strip mode and any subscene segment represents an artifi-
cial window that is extracted from a long digital image and defined in a uniform coordinate system.
The fact that the IRS-1C PAN camera has three CCD arrays offers a possibility to simultaneously
adjust the images acquired by them by exploiting the knowledge of inter-CCD alignment angles.
Currently, many remote sensing sensors exist that can be practically used for space cartography, includ-
ing IRS-1Cr1D PAN. Successful exploitation of the high accuracy potential of these systems depends on
good mathematical models for the sensor modelling. A number of papers have been published on different
approaches for the position and attitude determina-
Ž .
tion of these sensors Westin, 1990; Dowman, 1991 . The approaches differ in the use of constraints and in
the methods of determining the initial values of the unknowns. These methods demand multiple control
points for sensor modelling and orientation. The requirement of highly accurate control is a major
problem in remote areas, where IRS-1C PAN images are most useful for topographic mapping. Therefore,
with the aim of reducing the control requirements to a minimum, a model for the orientation of full
IRS-1C PAN scenes was developed.
The approach was initially developed for a single image and strip, but has been extended in this study
to include a block of subscenes. The satellite position is derived using the collinearity condition equations.
The initial orbit is obtained from the given ephemeris data and refinement is carried out using an iterative
least squares solution. This can be done directly, as long as the digital image data is given in a fully
continuous stream of scan lines in a uniform time frame. The method described represents a rigorous
geometric reconstruction of ground coordinates from IRS-1C PAN images. This method of processing is
ideal when the following conditions exist:
Ø multiple, monoscopic coverage from different de-
tectors during the same pass are available; Ø
minimal control points are available or cost con- Ž
siderations require reduction of used control in this model, a minimum of one GCP for process-
. ing is required ; and
Ø the desirable geometric accuracy is to be compa-
rable with the input GCP accuracy or the resolu- tion of the sensor.
2. Adjustment model
