Unambiguous Doppler Shift Estimation for Moving Targets with High Range Velocity Using SAR Data

This paper presents a new methodology to retrieve slant-range velocity estimates of moving targets inducing Dopplershifts beyond the Nyquist limit determined by the pulse repetition frequency (PRF ). The proposed approach exploits the linear dependence (not subject to PRF limitations) of the Doppler-shift with respect to the slant-range velocity, at each wavelength. Basically, we propose an algorithm to compute the skew of the two-dimensional spectral signature of a moving target. Distinctive features of this algorithm are its ability to cope with strong range migration and its e ciency from the computational point of view. By combining the developed scheme to retrieve the slant-range velocity with a methodology proposed elsewhere to estimate the velocity vector magnitude, the full velocity vector is unambiguously retrieved without increasing the mission PRF . The e ectiveness of the method is illustrated with simulated and real data. As an example, slant-range velocities of moving objects with velocities between 6 and 12 times the Nyquist velocity are estimated with accuracy better than 3%.