ON-ORBIT GEOMETRIC CALIBRATION OF THE 
ORBVIEW-3 HIGH RESOLUTION IMAGING SATELLITE 
David Mulawa, Ph.D 
ORBIMAGE, 1835 Lackland Hill Parkway, St. Louis, MO 63146, USA — mulawa.david@orbimage.com 
KEY WORDS: calibration, geometric, satellite, camera, accuracy 
ABSTRACT: 
Current high resolution satellite design includes several sensor types such as: GPS receivers, star trackers, rate gyros and 
cameras. In order to produce high quality metric imagery, the on-orbit data from all of these sensors need to be combined in a 
calibration process to produce the geometric model parameters of the sensor system. The calibration process is also used to 
determine an on-orbit stochastic model for the sensors and the estimated calibration parameters. 
The OrbView-3 (OV-3) on-orbit geometric calibration is based on the mathematical modelling and estimation of calibration 
parameters incorporated into a rigorous and flexible self-calibration triangulation, Kalman filter software suite and orbit 
determination software. The principal components of the geometric model are: orbit determination, attitude determination 
and camera model. The satellite orbit determination is based on the GIPSY-OASIS software from Jet Propulsion Lab (JPL). 
The calibration of the attitude determination system uses an Alignment Kalman Filter to estimate the alignment angles and 
gyro scale factor calibration parameters associated with the star trackers and rate gyros. Medium scale aerial imagery is used to 
form the basis of a geometric camera calibration range. To reduce the collection time and improve the quality of the camera 
calibration solution, the calibration range imagery is combined with image correlation software techniques to automatically 
acquire tie points with the satellite imagery and to allow the assembly of an extremely dense collection of ground control 
points ÿ 
The operational geolocation accuracy performance of the OV-3 satellite is represented by the observed geolocation accuracy at 
several test sites. 
1. INTRODUCTION 
Imaging satellites are subjected to several factors that may 
cause the values of the geometric calibration parameters to 
vary between the time of ground calibration and on-orbit 
operation. Some of these are: launch shock; loss of moisture 
due to vacuum; and gravity release. The ground calibration 
process is used to obtain the best a priori estimates of the 
on-orbit values of the, calibration parameters. Generally, the 
satellite builder can perform mechanical analyses to estimate 
the range in which the critical calibration parameters are 
expected to change between ground calibration and on-orbit 
use. 
The geometric calibration plan for the OrbView-3 (OV-3) 
satellite calls for an initial geometric calibration during the 
satellite commissioning phase and periodic geometric 
calibrations there after. There is a significant effort 
associated with the initial calibration. However, the 
accumulated magnitude of effort involved with the periodic 
geometric calibrations over the life of the satellite will 
surpass the one time initial effort. It is important that the 
on-orbit geometric calibration method be able to take 
advantage of autonomous methods as much as possible in 
order to drive down the effort and time required to perform 
the periodic geometric calibrations. 
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2. GEOMETRIC CALIBRATION RANGE 
The OV-3 Geometric Calibration Range is a metric standard 
that the OrbView-3 satellite data was compared against 
during geometric camera calibration. In order to provide the 
best geopositioning capability from the satellite systems, it 
is necessary that the calibration range have both good 
absolute and relative accuracies. 
Cost should also be considered. The calibration range 
should be cost effective to create, use and maintain. Two 
types of ranges can be considered: ground surveyed photo 
identifiable points and controlled aerial photography. The 
use of controlled aerial photography offers many 
advantages. For example, the calibration range is the set of 
aerial photographs and support data. As many ground 
control points as are needed can be generated from the set of 
aerial photographs. Powerful image correlation methods can 
be used to help reduce the cost and time needed to measure 
the control points in the aerial and satellite imagery. In 
terms of maintenance, if some of the photographs become 
unusable due to changes in the ground texture, such as new 
construction, additional aerial photography can be flown 
and triangulated into the block. 
The OV-3 Geometric Calibration Range covers an area of 
50km in the north-south direction and 50km in the east-west 
direction. The aerial photographs were acquired with a 
standard frame mapping camera at a scale of 1:25,000. All 
the points in the interior of the calibration range appear on a 
minimum of 4 photographs and some points fall on 9 
photographs. This redundancy leads to reliability suitable 
for a geometric calibration range. 
Ground control of the aerial photographs was provided 
through targeted GPS survey points. The exposure stations 
of the aerial photographs were acquired with differential GPS 
in order to: increase redundancy; stiffen the block; and to 
allow an improved self-calibration of the aerial mapping 
camera. 
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