Use of Doppler Parameters for Ship Velocity Computation in SAR Images

Abstract

This paper deals with the exploitation of Doppler centroid measurements for ship velocity estimation from focused single-look complex synthetic aperture radar (SAR) images. An algorithm is presented, which can be used as a discrimination tool to reduce the false alarm rate of standard adaptive threshold detectors and to complement the ship detection task with velocity estimation. The outputs are the indication of the presence of a moving target and the estimate of its slant range velocity. After a review of its theoretical background, algorithm features and performance are verified by application to TerraSAR-X data. The proposed method performs robust Doppler spectrum derivation for candidate ship targets and background pixels. The presented results show that the estimated radial velocity is in very good agreement (5% root-mean-square deviation) with that resulting from the azimuth offset method. Rejection of bright sea features and azimuth ambiguities is also demonstrated, taking advantage of the performed velocity analysis

Integration of Automatic Identification System (AIS) Data and Single-Channel Synthetic Aperture Radar (SAR) Images by SAR-Based Ship Velocity Estimation for Maritime Situational Awareness

“…Since the target DC is significantly different from both the background ones, one can conclude that the target box includes a ship, which is moving at about 2.5 m/s radial velocity. The method has been tested on X-band single-channel SAR data [40] showing very good agreement with velocities computed by the azimuth offset method.…”

“…However, these techniques require multi-channel or multi-static SAR systems which are currently not available from space [34]. Nonetheless, suitable techniques have been developed that are able to derive the radial velocity even from single-channel SAR images [12,[35][36][37][38][39][40][41][42].…”

“…The applicability is limited by the local conditions, such as wind speed and sea state. In most of the cases [12,35,[37][38][39][40]43] a detectable ship signature covering several image pixels is required, whereas other techniques [36,41] need a well-imaged wake pattern, which is an even rarer case and sets specific requirements on SAR image polarization. However, the analysis of the case study presented in this paper will indicate that when a SAR-based estimate of the radial velocity is available, it is worth using it.…”

“…In this case a different technique, referred to as DC analysis, can be applied, which processes ship signatures only. The method has been introduced in [40] and it is based on the consideration that the SWMF does not completely suppress the difference between stationary and moving targets, especially in the Doppler domain. The Doppler history of a moving target is characterized by a different Doppler rate and a different DC with respect to the stationary target case.…”

“…Incoherent combination is used to achieve noise and interference reduction. The DC estimation can be carried out by applying the clutterlock algorithm to the oversampled spectrum [40] or by polynomial interpolation of Fourier transform coefficients. In this paper the DC has been computed as the frequency corresponding to the maximum of the parabola interpolating the azimuth processed bandwidth of the spectrum [50].…”