APES (Amplitude and Phase EStimationl is an adaptive FIR filtering approach introduced recently for complex spectral estimation. For stationary signals, APES can yield more accurate spectral estimates than the widely used Capon and FFT estimators. The authors present a recursive APES algorithm for time-varying spectral analysis, which is computationaly efficient and only involves FFT and simple matrix operations. The recursive APES algorithm is applied to ISAR (inverse synthetic aperture radar) imaging and feature extraction of targets with complex manoeuvring motion. Both numerical and experimental examples are provided to demonstrate the performance of the proposed method.

An adaptive ground bounce (GB) removal algorithm is presented for landmine detection with a downward looking stepped frequency ground penetrating radar fGPlU．The main idea is to estimate and eliminate the GB from a givq3n scan as a shifted and scaled version of an adaptively estimated reference GB. Experimental results are provided to demonstrate that the new algorithm outperforills existing approaches.

Range-Doppler (RD) algorithms are widely used in inverse synthetic aperture radar (ISAR) imaging. In the standard RD algorithm, envelope alignment and autofocus are first applied to transform the original data into equivalent turntable target data, and then FFT is used for the image formation. Usually, the migration through resolution cells (MTRCs) due to target rotation is ignored. With the improvement of resolution or the increase of target size, MTRCs cannot be ignored and must be mitigated. For high speed moving targets, the most widely used 'stop-and-go' data model is violated. In this case, the mitigation of MTRCs becomes even more complicated. In the paper, technical issues associated with high resolution ISAR imaging of high speed moving targets are addressed. A preprocessing algorithm is first proposed to convert the non-coherent raw ISAR data into coherent data, then a keystone formatting algorithm developed for the imaging of slow ground moving targets in SAR is applied to mitigate the MTRCs owing to rotational motion, and, finally, a high resolution time-frequency analysis based range-instantaneous Doppler (RID) algorithm is used to produce the focused ISAR image. Numerical examples are provided to illustrate the performance of the proposed approach.

To detect buried landmines, Planning Systems Incorporated (PSI) has developed a Ground Penetrat-ing Synthetic Aperture Radar (GPSAR) system. GPSAR can be used to generate three-dimensional images of mines. It has been shown that the SAR processing in the PSI GPSAR system can greatly improve the image quality and hence the mine (especially plastic mine) detection performance. Since the electromagnetic wave propagation velocity in the soil depends on many factors, inchlding the soil texture, bulk density, as well as water content, and it changes from one location to another, velocity uncertainty is inevitable. It is well-known that for the conventional airborne/spaceborne SAR processing, velocity uncertainty may result in phase errors that will severely blur the SAR image. However, we have observed from experimental examples that the PSI GPSAR system is very robust against the velocity uncertainty. More specifically, under mild conditions velocity uncertainty does not defoeus the image but only scales the image along the depth dimension, and hence will not affcct the mine detection performance. Theoretical analysis is provided to explain this observation. Although our discussion is based on the PSI GPSAR system, it applies to other GPR based landmine detection systems as well.

With conventional pulse-echo ranging approaches it is diffcult to obtain un accurate range measurement needed by a proximity ultrasonic sensor system owing to the limited bandwidth of the transducer. A continuous-wave multifreouencv ranging method is presented to accurately measure the proximity distance for an ultrasonic distance sensor system A novel time delay estimator is derived based on a nonlinear least-squares-fitting criterion for the case where the received signal amplitude is non-negative owing to the acoustically hard reflection To minimise the highly oscillatory cost function an effcient two-stage estimation algorithm is proposed Numerical results show that the estimation algorithm can approach the Cram6r-Rao bound as the signal-to-noise ratio increases.