We present analysis methods that may be used to geolocate emitters using one or more moving receivers. While
some of the methods we present may apply to a broader class of signals, our primary interest is locating and
tracking ships from short pulsed transmissions, such as the maritime Automatic Identification System (AIS.)
The AIS signal is difficult to process and track since the pulse duration is only 25 milliseconds, and the pulses
may only be transmitted every six to ten seconds. Several fundamental problems are addressed, including
demodulation of AIS/GMSK signals, verification of the emitter location, accurate frequency and delay estimation
and identification of pulse trains from the same emitter. In particular, we present several new correlation methods,
including cross-cross correlation that greatly improves correlation accuracy over conventional methods and cross-
TDOA and cross-FDOA functions that make it possible to estimate time and frequency delay without the need of
computing a two dimensional cross-ambiguity surface. By isolating pulses from the same emitter and accurately
tracking the received signal frequency, we are able to accurately estimate the emitter location from the received
D. J. Nelson and J. L. Townsend, "Multi-ball and one-ball geolocation and location verification," Proc. SPIE 10202, Automatic Target Recognition XXVII, 102020S (Presented at SPIE Defense + Security: April 11, 2017; Published: 1 May 2017); https://doi.org/10.1117/12.2271698.
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