Velocity retrieval of moving object from a single channel high resolution SAR data

Two-dimensional velocity retrieval methods from a single channel high resolution SAR data through a joint time-frequency analysis and a fractional Fourier transform (FrFT) are presented. Two-dimensional velocity can be measured by estimation of the Doppler center frequency and Doppler frequency rate for the range and azimuth velocity component, respectively. The Doppler spectrum along a Doppler phase history line in the time-frequency domain was reconstructed and projected onto the frequency and time dimension. The peak of the frequency-axis projected spectrum corresponds to the Doppler center frequency, while that of the time-axis indicates an azimuth time of closest approach. The Doppler frequency rate is also measured by the slope deviation of the Doppler spectrum. Simulation using TerraSAR-X parameters indicated that the velocity errors were less than 1 m/sec or 5% for moving objects with a velocity higher than 3 m/sec. While the measurement of Doppler center frequency was reliable over the entire velocity range, errors in Doppler frequency rate became large if the velocity was lower than 3 m/sec. An experiment using TerraSAR-X and truck-mounted corner reflectors validated the measurement accuracy of the approach. Absolute and percent errors of the range velocity were 1.4 km/h and 2.8%, respectively, while the azimuth velocity measurement was comparatively accurate under an assumption of zero acceleration. To apply the method to single-look complex data, the full Doppler bandwidth must be preserved. Application of a fractional Fourier transform (FrFT) to the same data is also presented. The FrFT approach significantly improves computational efficiency and is superior to the WVD approach in estimation of Doppler frequency rate.