Abstract
A relatively unknown yet powerful technique, the so-called fractional Fourier transform (FrFT), is applied to SAR along-track interferometry (SAR-ATI) in order to estimate moving target parameters. By mapping a target's signal onto a fractional Fourier axis, the FrFT permits a constant-velocity target to be focused in the fractional Fourier domain thereby affording orders of magnitude improvement in SCR. Moving target velocity and position parameters are derived and expressed in terms of an optimum fractional angle a and a measured fractional Fourier position up, allowing a target to be accurately repositioned and its velocity components computed without actually forming an SAR image. The new estimation algorithm is compared with the matched filter bank approach, showing some of the advantages of the FrFT method. The proposed technique is applied to the data acquired by the two-aperture CV580 airborne radar system configured in its along-track mode. Results show that the method is effective in estimating target velocity and position parameters.
Highlights
Canada’s RADARSAT-2 commercial synthetic aperture radar (SAR) satellite, to be launched in spring 2006, will have an experimental mode that will allow the full antenna to be broken into two subapertures with two parallel receivers to define two independent data channels [1]
In addition to the dual-receive mode of operation, RADARSAT-2 will support an alternating-transmit mode where pulses are transmitted alternately from each wing and received alternately on each wing. This mode allows greater separation of the two-way phase centers in the along-track direction and the possibility of generating a third phase center for three-aperture ground moving target indication (GMTI). This mode of operation is currently being investigated in preparation for RADARSAT-2 MODEX demonstration but is not examined in this paper, since it has been recognized that a two-aperture approach is suboptimum [2, 3]
The ability of a matched filter to focus an accelerating target does not necessarily mean that the target’s parameters can be estimated more than the fractional Fourier transform (FrFT) approach. As it turns out, the obvious advantage of the FrFT method is that it has fewer intermediate parameters to be estimated than the MF approach in the case of constant velocity targets, making the FrFT method a more robust and preferred technique
Summary
Canada’s RADARSAT-2 commercial SAR satellite, to be launched in spring 2006, will have an experimental mode (called MODEX for moving object detection experiment) that will allow the full antenna to be broken into two subapertures with two parallel receivers to define two independent data channels [1]. In addition to the dual-receive mode of operation, RADARSAT-2 will support an alternating-transmit mode where pulses are transmitted alternately from each wing and received alternately on each wing This mode allows greater separation of the two-way phase centers in the along-track direction and the possibility of generating a third phase center for three-aperture ground moving target indication (GMTI). Moving target signals are embedded in the imaged stationary scene, which is called “clutter.” The interferometric phase φATI is often used to estimate a target’s radial velocity and azimuth shift, without considering the fact that φATI is corrupted by the overlapping stationary clutter (cf [5]). Moving target position and motion parameters can be derived and expressed in terms of a best FrFT angle α and position up, which can be computed from the experimentally measured data
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