David Mulawa 
  
PREPARATIONS FOR THE ON-ORBIT GEOMETRIC CALIBRATION 
OF THE ORBVIEW 3 AND 4 SATELLITES 
David Mulawa, Ph.D. 
ORBIMAGE 
mulawa.david@orbimage.com 
KEY WORDS: Geometric, Camera, Calibration, and Satellite 
ABSTRACT 
A new generation of commercial satellites offers 1 meter resolution, GPS orbit tracking with star tracker and gyro 
attitude determination. This powerful combination of sensors can be used to precisely locate positions on the Earth 
without the need of ground control points. However, this goal can only be realized after the sensor suite has been 
properly calibrated on-orbit. 
A robust system for on-orbit geometric calibration is composed of several essential components: computer hardware 
and software, and geometric calibration range(s). This paper discusses a Geometric Calibration System to address these 
necessary tasks for the geometric calibration of the OrbView 3 and 4 satellites. 
The OrbView on-orbit Geometric Calibration System is based on the mathematical modeling and estimation of 
calibration parameters incorporated into a rigorous and flexible self-calibration triangulation and Kalman filter software 
suite. Medium scale aerial imagery is used to form the basis of a geometric calibration range. To reduce the collection 
time and improve the quality of the calibration solution, the calibration range imagery is combined with powerful 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. 
The components used in the OrbView Geometric Calibration System are easily modified to perform geometric 
calibrations of other satellite or aerial imaging systems. 
1 BACKGROUND 
Imaging satellites are subjected to several factors that may cause the value of the geometric calibration parameters to 
vary between the time of ground calibration and their use on-orbit. 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 analysis to 
estimate what range the critical calibration parameters are expected to vary between ground calibration and on-orbit use. 
After calibration, the OrbView satellites will have the capability to position points on the Earth without need of ground 
control points. Determining positions without ground control points and by using only the satellite data is known as 
stand alone positioning. The accuracy of stand alone positioning relies heavily on the quality of the geometric 
calibration. An incorrect geometric calibration can result in unaccounted for systematic errors (biases). If unaccounted 
systematic errors are present after the geometric calibration, their effects may be driven down into the determination of 
object space positions. Furthermore since no ground control points were used, the results of the systematic errors may 
not be easily discovered leading to a possible false sense of accuracy of the stand alone positioning capability of the 
satellite system. If ground control points are available, they can be used with the OrbView 
The geometric calibration plan for the OrbView 3 and 4 satellites calls for an initial geometric calibration during the 
satellite commissioning phase and a monthly geometric calibration there after. There is a significant effort associated 
With the initial calibration. However, the accumulated magnitude of effort involved with the periodic monthly 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 monthly geometric calibrations. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part Bl. Amsterdam 2000. 209