Demonstration of target vibration estimation in synthetic aperture radar imagery

Abstract

Synthetic-aperture radar (SAR) can be used to remotely estimate ground target vibrations by exploiting the Doppler in the returned signals. Recent studies suggest that timefrequency signal-processing tools can retrieve the vibration signature from the returned SAR signals. A vibration estimation method based on the fractional Fourier transform (FRFT) was reported earlier and it was tested on simulated SAR data. In this paper, a first-time demonstration of the FRFT-based vibration estimation method is reported using real SAR data collected by the Lynx (K u -band) SAR system. The vibrating target is an aluminum triangular trihedral with lateral length of 15 inches. The FRFT-based algorithm is shown to successfully retrieve a 3 mm peak-to-peak amplitude, 5 Hz vibration of the target from real SAR data.

Limitations and capabilities of the slanted spectrogram analysis tool for SAR-based detection of multiple vibrating targets

“…Fig 7-8 shows that as the value of K increases the slanted and conventional spectrogram gradually fail to detect all targets. Therefore, we can conclude that if the minimum measurable chirp rate for the slanted spectrogram (K min = 0.001rad/samples 2 ) denotes the stationary target's chirp rate and using K min as a lower limit measure for detecting the vibration acceleration, since it had been established in [8] that the chirp rate K is directly proportional to the vibration acceleration a v for a target signal. For values of K > K min , the ratio of detection ρ k = K/K min was used to estimate the threshold for the slanted spectrogram to be within range 1 < ρ k ≤ 4.5 and the improved spectrogram detects all target regardless of the value of K. This can be used to estimate the value of the vibration acceleration a v of targets.…”

“…Vibration signatures associated with objects such as active structures and vehicles can bear vital information about the type and integrity of these objects [3]. These vibrating objects cause phase modulation of the azimuth phase history for a SAR system and this phase modulation is seen as a time-dependent micro-Doppler frequency [8] which is useful for analyzing such signals with appropriate time-frequency methods in order to preserve it superior resolution potential [2].…”

Clutter suppression in synthetic aperture radar targets using the DFRFT and subspace methods with rank reduction

“…(1). Prior work in [2], [3] did not incorporate rank-reduction and filtering of the subspace signals to remove clutter that manifests as high-frequency noise in the center-frequency and chirp-rate slices. Rank reduction employs correlation matrices that retain just the signal or noise subspace, thereby rejecting noise and clutter prevalent in the other subspaces [1].…”

“…In recent years, the DFRFT [7], [8], [9], [6] has become a useful time-frequency tool for multiple chirp parameter estimatiolin [5] and in particular it has been successfully applied to the problem of vibration estimation using SAR [2], [3], [4]. Direct DFRFT based estimation of the vibration frequency involves application of the DFRFT to the target return signal, peak coordinate location and translation of the peak coordinates to center-frequency and chirp-rate estimates using the peak-to-parameter mapping.…”

Performance analysis on synthetic aperture radar-based vibration estimation in clutter

“…The target vibration can be estimated through successive chirp-rate estimations using the discrete fractional Fourier transform (DFrFT), which is inherently geared toward chirprate estimation [3], [4], [5], [6], [7]. Later on, a subspace method was incorporated into the DFrFT-based method and it provides better performance than the direct DFrFT-based method in noise [8], [9].…”