In a previous SPIE paper we described several variations of along-track interferometry (ATI), which can be used for
moving target detection and geo-location in clutter. ATI produces a phase map in range/Doppler coordinates by
combining radar data from several receive channels separated fore-and-aft (along-track) on the sensor platform. In
principle, the radial velocity of a moving target can be estimated from the ATI phase of the pixels in the target signature
footprint. Once the radial velocity is known, the target azimuth follows directly. Unfortunately, the ATI phase is
wrapped, i.e., it repeats in the interval [-π, π], and therefore the mapping from ATI phase to target azimuth is non-unique.
In fact, depending on the radar system parameters, each detected target can map to several equally-likely azimuth values.
In the present paper we discuss a signal processing method for resolving the phase wrapping ambiguity, in which the
radar bandwidth is split into a high and low sub-band in software, and an ATI phase map is generated for each. By
subtracting these two phase maps we can generate a coarse, but unambiguous, radial velocity estimate. This coarse
estimate is then combined with the fine, but ambiguous estimate to pinpoint the target radial velocity, and therefore its
azimuth. Since the coarse estimate is quite sensitive to noise, a rudimentary tracker is used to help smooth out the phase
errors. The method is demonstrated on Gotcha 2006 Challenge data.