Two of the most important missions of Shiran are the 
line crossing and controlled photography• Referring to 
Figure 3, the objective of the line crossing is to deter 
mine the ground distance between two transponders. This 
is accomplished aerially by ranging to the two transponders 
while flying between them. A parabolic curve is formed if 
you plot the range sum (Ri + R2) versus time. The minimum 
range sum denotes the point at which the line between the 
two transponders was crossed. Having obtained this, the 
distance between the two stations can be calculated. Shiran 
obtains this minimum sum. It can determine the minimum sum 
with but 1-mlnute or less of range data taken in the vici 
nity of the center line. The objective of the controlled 
photography mission is to position the nadir points of 
photographs for mapping applications. This is accomplished 
by flying parallel flight lines and taking photographs with 
specified overlap and sidelap (Refer to Figure 4). Shiran 
range information is continually recorded to four ground 
stations. A camera trigger pulse, denoting midpoint of 
shutter opening, is also recorded. With known ground sta 
tion positions, the location of the nadir point of each 
photograph can be determined. Though Shiran ranges are 
continually recorded, only a 10 to 20-second span around 
the camera trigger need be used. Advantages of the four