Interferometry against differential Doppler: performance comparison of two emitter location airborne systems

A comparative random error analysis of two airborne systems that provide the location of a stationary emitter is presented. Both systems utilise only two airborne receivers. In the interferometric system, the separation between the receivers (baseline) is of the order of one wavelength, and the phase measurements yield bearing measurements. In the differential Doppler system, the baseline can extend to the full length of the aircraft, and phase measurements yield accumulated range difference. Both systems employ the Gauss-Newton iterative algorithm to obtain an unbiased, least-squares estimate of the emitter location. Simple analytical expressions are obtained for the random error of both systems when the observation section is centred near the point of closest approach. Results of Monte-Carlo computer simulations are also presented, which confirm the theoretical error expressions.