Development of a Precise Geodetic Survey System

The development of a system to perform first-order airborne geodetic surveying is described. It is shown how existing distance measuring techniques were applied to solve the operational requirement for a system that can measure the length of lines up to 900 nautical miles long with a probable error of 0.0017 nautical miles, and determine the nadir points of aerial photographs within twenty-four feet for ninety percent of the measurements. The implementation of the Distance Measuring Equipment (DME) using a CW carrier phase modulated by four ranging tones is described at the block diagram level, it is shown that modulation with a large index (twelve radians) reduces the ranging errors associated with multipath propagation which formerly were a significant source of error in DME systems. Results of a flight test program are presented.