14 
PROPOSALS FOR RADIOMETRIC AND GEOMETRIC ON-LINE CORRECTIONS OF AIRBORNE CCD-PUSH 
BROOM SCANNER DATA 
Dr. M. Scheele, Dipl.-Phys. Th. Terzibaschian 
German Aerospace Research Establishment 
Institute for Space Sensor Technology 
Adlershof 
Rudower Chaussee 5 
D-12489 Berlin 
4 -49 30 69545 521/586 
FAX: +49 30 69545 572 
E-mail terzi@ hardy.ws.ba.dir.de 
KEY WORDS: CCD Push Broom scanner, image correction, on-line photogrammetry 
ABSTRACT 
In the next future it should be possible to make photogrammetric products quasi on-line. CCD line scanner will play an 
important role in on-line photogrammetry. Some problems will be discussed. It is shown, that on-line photogrammetry 
has to use the collinearity equations for a certain projection plane and the velocity vectors in that plane. Then, geome- 
tric and radiometric image corrections can be done. As one example of active methods, the CCD clock control will be 
discussed. This can avoid uncorrectable image gaps. 
1. MOTIVATION 
One challenge of the next future is on-line photogrammetry. This means the on- line generation of ortho-photos and 
DTM on board of airplanes or satellites. It becomes now possible because of the fast technical progress concerning 
inertial navigation systems, gyros and positioning systems. On-line photogrammetry will decrease the costs and 
increase the speed of DTM generation or updating DTM. Actually there are a lot of reasons, that the CCD line scanner 
will play an important role even comparing it with CCD matrices (OEEPE,Paris 1994). 
Comparing it with classical Photogrammetry it is necessary to reduce the pixel size by a factor two and to increase the 
pixel number up to 23..30 Kpixel. But even today many users could live with the lower resolution of present CCD lines 
as for example the telecommunication or road building companies. Another important filed is the detection and 
monitoring of catastrophes and the fast evaluation of their consequences (landslides, fire, flood disaster)(see for example 
Jahn et al., 1994). Low cost and „fast reaction“ photogrammetry will prefer airborne use of scanners. 
But this is connected with the disadvantages of the rather irregular airplane motion (yaw,pitch,rol, altitude and velocity 
variations) which can make the photogrammetric use of image data quite impossible. It is only possible, when all 
attitude data are known with a sufficient accuracy and time resolution. Another way is the use of stabilised platforms. 
But this is rather expensive and is not our topic and our way. Algorithms, which do the geometrical image correction 
only by using all available attitude and positioning information are important for the actual and future photogrammetry. 
One of the most sensitive steps of the photogrammetry is to find corresponding image points in a stereo image pair. 
This matching is strongly influenced by radiometric and geometric image disturbances. One line scanners as imaging 
spectrometers have to do the orthophoto projection without additional pass point information. There is a close relation 
between radiometric and geometric resolution. Scenes with low contrast can be imaged with a better geometric 
resolution, when the radiometric resolution is sufficient. The stereo matching uses correlation algorithms of grey level 
values. The correlation functions are directly affected by the signal/noise ratio. The consequence is, that radiometric on- 
line corrections are an essential part of on-line photogrammetry. It is the state of the art to do the most important 
radiometric corrections on-line as: dark signal correction, pixel related photo response non uniformity (PRNU) and 
even/odd channel deviations. (Sandau, R., 1994, Eckardt 1995). This problem is solved. 
The contents of this report will be the completion of necessary equations to describe the imaging process with respect 
to its dynamic. Then we will analyse the consequences of this equations and we make one next step toward to on-line 
photogrammetry by controlling the CCD clock rate. 
2. A MATHEMATICAL FORMULATION OF DYNAMIC IMAGING PROCESS 
The parts from two WAOSS (Wide Angle Optoelectronic Stereo Scanner) stereo image pairs (raw data after radiometric 
on-line correction) illustrate the influences of the irregular airplane motion(Fig.1). In the worst case the interference of 
all disturbances (yaw, pitch, roll ..) make it impossible, to realise details. The matching of corresponding image points is 
impossible. But using the attitude information this image can be corrected and even in the most damaged parts you 
can find details. The known bundle adjustment (Müller,1991) can not be used, as the number of orientation images 
would be too high. In order to evaluate the disturbances we have to compare the relation of the pixel IFOV and the 
IAPRS, Vol.30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995 
  
  
Fig. 
Of c 
This 
Zz 2, 
A na 
dista 
The 
ratio 
terra 
Real 
time. 
moti 
The. 
At le 
angu 
to ot 
and | 
This 
by it 
plan 
JAPF