(10) 
The equipment in use is that available from World War II stock and has been 
modified to improve its use in shoran. Gradual replacement of new airborne and 
ground equipment is taking place and this will, no doubt, contribute to improved 
accuracy. Automatic gain control to offset variable signal strength has been tried 
but so far without success. The attachment of an errorscope to the airborne 
recorder, by which irregularities in the matching of pulses may be assessed and 
corrected for, is believed to be of more value in photographic missions than in the 
line-crossings and to date has not been used. Neither has radar altimetry. 
Difficulty has been experienced in calibration. Nevertheless the results are 
indicated as more than sufficient for the purpose in mind, that of shoran-controlled 
photography. Further, the shoran net is not intended to replace triangulation in 
local areas and future extensions northward of first-order work will give more 
attachments for the shoran net and thus make it possible to improve its general 
overall placement. In this it is admitted that difficulty exists in maintaining direc 
tion over long distances by shoran with the present equipment and methods. Four 
Laplace azimuths have been introduced in the net to offset this tendency to weave 
in direction. 
Application to Mapping 
The application of the shoran system to mapping depends upon the making 
of instantaneous length measurements from the plane on photographic mission to 
two established shoran stations. In bombing operations the system was used as a 
navigation aid to indicate the on-target and bomb-release position according to 
previous calculation. In mapping the bomb gives way to the vertical camera and 
photographs of the shoran dials simultaneous with the camera exposures of the 
terrain correspond to the bomb release. The timing unit is airborne and the slope 
distances from the aircraft to the two ground stations used as a base can be 
determined from the data. When the position and elevation of each ground station 
and the height of aircraft are known, the projected position of each vertical photo 
may be computed. 
The accuracy of these shoran fixes cannot be any more precise on the 
average than the capability of the shoran operator in matching the return pips 
with the marker pip on the oscilloscope screen. In line-crossing this operation is 
strenuous enough but on photo-flights when the aircraft may be on flight lines for 
thirty minutes or more instead of five, fatigue may contribute very seriously to 
inaccuracy. In addition, there is but one value of each of the slope distances, 
that at the time of photo exposure. Delay values, goniometer errors, and other 
factors have an effect on scale as well as in direction of the plot, but as a rule it is 
possible to alter and shift the plot to give a very good placement. 
More factors must be considered in the planning of a shoran-controlled flight 
operation than with conventional methods. The spacing of flight-lines and fore 
and aft overlap called for do not change as they are dictated by the flying height 
and ground relief. The location of the ground stations in respect to the flight area 
is very important. The airborne set must always be within the effective range of 
the ground stations, while for best results the angle subtended at the aircraft by 
these two points should lie between 60 and 120 degrees. The path of the shoran 
ray may be considered for all practical purpose as “line of sight”; this means in a 
certain sense that the ground station and aircraft must be intervisible for efficient