6. IMAGE PROCESSING 
The raw imagery looks bizarre, because aircraft tilts 
and terrain relief cause the linear arrays to image 
widely varying strips of terrain, which is well 
known. Fig. 13 shows imagery acquired by the nadir 
sensor of the new camera over Berlin. The flight 
direction was from left to right. The top image is 
raw. The bottom image has been rectified and looks 
similar to a conventional aerial photograph. Note the 
correspondence between the edges of the rectified 
image and the roll of the aircraft. Tilts have been 
compensated by adjusting each individual scan line 
for the attitude of the aircraft, using data from the 
airborne GPS and INS units carried on every fight. 
An initial rectification using these data is essential 
even to view the imagery. Thereafter, operations 
such as triangulation, DTM measurement, 
orthophotos and feature extraction continue in the 
usual way. Automated processes, such as point 
measurement for triangulation and DTM extraction, 
can be based on triplet matching using the three 
strips. 
Roll 
Pitch 
Yaw 
Fig. 13. Imagery acquired by the new sensor over Berlin. 
Owing to their positions on the focal plane, 
combined with the aircraft and terrain variations, the 
colour lines image slightly different parts of the 
earth’s surface. Thus full rectification is required, i.e. 
orthophotos are produced, before the colour bands 
can be properly registered and transformed into 
colour composite images suitable for analysis by off- 
the-shelf remote sensing packages.