Locating emitters using a cross-spectral cross-ambiguity function (CSCAF)

We present two methods to accurately estimate the location of an emitter from the received signal. The first of these methods is a variation of the standard cross-ambiguity function (CAF) for which we introduce a cross-spectral frequency estimation technique to replace the conventional methods based on the power spectrum. We demonstrate the use of the CSCAF in estimating the source location of an RF emission. The CSCAF is computed as the product of the complex-valued CAF and the conjugate of the time-delayed CAF. The magnitude of the CSCAF is the conventional CAF energy surface, and the argument of the CSCAF is the unquantized frequency difference of arrival (FDOA) computed as the phase of the CAF differentiated with respect to time. The advantage of the CSCAF is that it provides an extremely accurate estimate of FDOA. We demonstrate the use of the CSCAF in providing emitter location estimates that are superior to those provided by the conventional CAF. The second method presented provides a precision geolocation of the emitter from the signal received by a single moving receiver. This method matches the Doppler characteristics of the received signal to the Doppler characteristics estimated from the geometry of the transmitter and receiver. Both the CSCAF and the single receiver methods are enabled by cross-spectral frequency estimation methods that provide extremely accurate frequency estimation and tracking.