modifving these address registers. 
- Subroutine jump, conditional return from subroutine, loop control in- 
structions, but no branch instructions are provided. 
Forimage processing applications, the virtual machine is incorporated 
in a program which reads a mui*ispectral image from disk line by line, 
transfers control to code generated through the virtual machine, which 
operates on that data, and writes the resulting image line onto the COM- 
TAL display refresh memory and optionally to an output disk file. 
The data format on disk is determined by execution time and disk space 
considerations. The format adopted provides a 256 x 256 point image of 
up to nine channels in direct access records of 256 16-bit numbers, each 
record corresponding to one line and one channel. 
A tape of OCS date a3 acquired on June 27, 1977, contains about 1:0 
scan lines of 440 points each (data acquired on the other flight days are 
formatted differently). For covering a reasonable large area with a disk 
file, the averacc value of 2 x 2 points of the originai data is stored as one 
value on the disk file, yielding an image of about 220 v» 256 points. The 
areas to be worked on were selected such that full ship tracks are cover- 
ed. As channel 9 of OCS is optimized for radiances over land, it was the 
natural choice of a channel to be omitted. 
4, Correlation of sea truth and scanner data 
  
A first requirement for correlating image data with sea truth is a proce- 
. dure for locating points with given geographica: coordinates on the image. 
Since on water few, if Any, ground control points can be identified on the 
image, such à procedure must rely on flight attitude and “can geome- 
try data. The program GEC, creiuted and used for the work presented, 
requires one control point of which the geographical coordinates are 
known, to be located on the image, and computes the correspondence 
between geographica. and irrage coordinates for any selected point in the 
image, using flight and scanner parameters which are assumed to be 
constant over the whole image. The positions of the selected points can 
be given in either geographical or image coordinates. Optionally, for 
any point on the image radiance values as measured by the scanner, can 
be extracted. 
By comparing the coast line visible in the imagery with a digitized map 
which was superposed to the image and displayed on the graphics over- 
lay using GEO, discrepancies between computed and actual positions 
could be observed and the flight and scan parameters could be correc - 
ted appropriately. 
   
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