ISPRS Commission III, Vol.34, Part 3A „Photogrammetric Computer Vision“, Graz, 2002 
  
LABORTARY SELF-CALIBRATION OF A MULTI-BAND SENSOR 
Abdullatif Alharthy, James Bethel 
School of Civil Engineering, Purdue University, 1284 Civil Engineering Building, West Lafayette, IN 47907 
alharthy@ecn.purdue.edu, bethel@ecn.purdue.edu 
KEY WORDS: Camera Calibration, CAMIS, Self-Calibration, image matching, radial distortion, decentering distortion 
ABSTRACT: 
CAMIS is a multi-band airborne remote sensing instrument and is designed to utilize modern solid-state imaging and data 
acquisition technology. It is composed of four CCD cameras with band pass optical filters to obtain four band images. In this paper, 
we summarize the geometric calibration procedure and results of the CAMIS sensor. We modified the conventional calibration 
procedure especially for this sensor to make the process more efficient. A network bundle adjustment program was developed and 
used to adjust the laboratory measurements and locate the targets. Images of the target field were then taken by each of the four 
cameras of the CAMIS sensor. Two matching techniques were used to determine and refine the target locations in the image space. 
We modified the matching algorithm to overcome certain radiometric effects and thereby found the location of the target centers in 
image space. 
A full math model was used to recover the most significant camera parameters. The unified least squares approach was used 
iteratively to solve this nonlinear overdetermined system. In order to determine the lens distortion behaviour, the radial and 
decentering components were estimated. Then the radial distortion curve was equalized and the corresponding changes to the 
sensor parameters were recorded. Finally, we present four sets of adjusted parameters, one per camera. For simplicity, the 
graphical user interface feature in MATLAB was used to create a small user-friendly window with an executable file to adjust the 
image measurements for the four images based on their parameters. 
1. INTRODUCTION 
CAMIS stands for Computerized Airborne Multicamera 
Imaging System. The CAMIS sensor consists of four co- 
boresighted area-CCD cameras with band pass filters: blue, 
green, red, and near infrared as shown in figure 1. In this 
paper, we summarize the work that has been done during the 
geometric calibration of the CAMIS sensor. The procedure 
required many preliminary steps such as preparing the 
calibration site which involved target layout, setting up the 
coordinate system and locating fiducial monuments within that 
system. Three arc-second theodolites and a steel tape were 
used to measure the angles and distances in the network of 
calibration targets. In order to adjust those measurements and 
to get the target coordinates into the reference coordinate 
system, we developed a network bundle adjustment program. 
Images of the target field were then taken by each of the four 
cameras of the CAMIS sensor. The coordinates of the targets in 
both the object and the image system were used as 
observations for estimating the sensor parameters in a second 
bundle program configured for self-calibration. 
The images were taken and the calibration procedure was 
started after planning the data flow. To cover the most 
significant conventional parameters, a full math model was 
used. This math model and its use are fully explained in 
(Samtaney, 1999) and also they are outlined in this paper. The 
unified least square approach was used iteratively to solve this 
nonlinear overdetermined system since we have some prior 
knowledge about a number of the sensor parameters (Mikhail 
and Ackerman, 1976). The parameters were classified carefully 
into measurements and fixed groups in order to get reliable 
results by minimizing the dependency between the parameters. 
Moreover, in order to see the distortion behavior, the radial 
and decentering distortions were calculated and plotted 
separately. Afterward, the radial distortion curve was equalized 
and the corresponding changes to the sensor parameters were 
recorded. We repeated the procedure for each camera 
individually and consequently our results have four sets of 
adjusted parameters, one per camera. The basic steps and 
algorithms that were used during the calibration process are 
outlined below. In the actual use of this imaging system, often 
three of the bands are registered and resampled to a reference 
band. In that case, only the calibration of that reference band 
would be used. 
    
Figure 1. CAMIS sensor (four cameras) hi 
2. CALIBRATION 
The aim of this work was to make a laboratory calibration for 
the geometric parameters of the CAMIS sensor. It is composed 
of four CCD cameras with band pass optical filters to obtain 
four band images. The center wavelength of those bands is as 
follows: 450, 550, 650 and 800 nm. However, each sensor has 
its own optics and obtains its own image independently from