derivative measurements in the processor. The whole 
process is identical to quadruplex correlation detec- 
tion. techniques described by the illustrations in 
Figures 4 and 5. 
AUTOMATIC OPTICAL SYSTEM 
A completely automatic stereo-image matching 
system must have the capability of detecting and 
correcting image misalignment and distortion as well 
as controlling the aperture size of the correlator. Such 
a system is illustrated in Figure 8. The major part of 
the system is the multi-aperture correlator shown in 
the previous figure. 
Image distortion correction is accomplished by 
means of a servo-driven anamorphic zoom system 
that is placed between the transform and imaging lens 
in the correlator. The system contains the necessary 
cylindrical and spherical lens elements to accommo- 
date for first-order image distortion. 
The correlator aperture is controlled by a servo- 
driven zoom lens system. Aperture control helps to 
maintain a constant loop gain through the system. It 
is required for accurate automatic stereo-image 
matching. Besides controlling the aperture, the zoom 
system conserves laser power. The zoom technique 
maintains a constant power level in the entrance aper- 
ture of the correlator. 
Aperture 
Zoom Control X and Y 
Collimated Alignment Control 
Laser Beam Signals 
Sh Î 
- » 
0) 7 
dno 
7 1 
£ 
EI ^ 
- > 
Photo 1 
T-Lens 
    
  
Anamorphic Image 
Distortion Correction 
System 
Image Scanner 
Photo 2 
The X and Y photo alignment servo-driven car- 
riages are not shown; however, the error signals are 
labeled and their function is depicted graphically in 
terms of photo 1. 
ELECTRONIC CORRELATION 
Present stereo image electronic correlation systems 
almost universally use flying-spot scanners as an inte- 
gral part of the system. The flying-spot scanners con- 
vert the pictorial information in the stereo diaposi- 
tives to electrical signals that are processed by the 
electronic correlator. A description -of the electronic 
image correlator, therefore, necessarily includes the 
scanner system. Indeed, the operational characteris- 
tics of the image correlator are usually limited by the 
performance of the flying-spot scanners. 
The basic elements of a flying-spot scanner correla- 
tor are shown in Figure 9. Each channel of the dual 
flying-spot scanner system contains a scan signal 
generator, a cathode-ray tube (CRT), a transfer lens, 
and a phototube. The dynamic performance of the 
scanner is illustrated in the drawing. The CRT gen- 
erates a scanning spot that moves in a fixed pattern 
called a raster; the scan signal generator controls the 
size and form of the raster. The transfer lens images 
the scanning spot and raster in the plane of the stereo 
diapositive. As the scanning spot moves across the 
Signal 
Processor 
Multi-Aperture 
Correlator Output 
  
  
  
  
  
  
  
Signals 
Scanner Vom 
Synch. Signals 
Distortion 
Detector 
I-Lens Quadrant Lens 
and Detector Assembly 2 
(es 
AA A 
NAVAS 
«T x 
v 
Beam Cr ss 
Expander N 
- 
77 f). ZA \ \ 
IN 
M /1 / = N 
ke A 
3 = 
x ~ 
> 
IN - E. 
> a 
~ Alignment 
DS £5 Detector 
/ s 
/ ^ 
Beam -d-- 
Splitter 
O- Lens 
Figure 8 Multi-Aperture Optical Stereo Image Matching Correlator S ystem 
THERMAL MAPPING 
77