This invention relates generally to radio detecting and ranging (radar) systems and, more specifically, to processing radar signals to automatically detect targets.
Currently developed automatic radar target detection systems generally lack accuracy needed for effective target detection. In particular, space-based radar systems may miss many targets or, on the other hand, may yield high false alarm rates. Generally speaking, current radar transducing technology is capable of providing the data needed to manually and automatically detect targets with greater accuracy. However, methods and systems used to process that data cannot automatically detect targets with sufficient accuracy.
As a result of the shortcomings of automatic target detection, aerial radar platforms relay image data to ground stations where human analysts manually inspect the image data for targets. This process is costly in many ways. Manual verification necessitates increased transmission bandwidth to get the image data to the human analysts. Further, staff of analysts presents considerable manpower and facilities costs. Moreover, this costly process is time-consuming, and therefore undermines the value of the resulting analysis. By the time an analyst receives, reviews, and renders a conclusion, the target may have moved, possibly out of range of further tracking and/or prosecution.
Current automatic target detection research tends to concentrate on systems based on single polarization radar systems. Single polarization radar provides only a single set of planar transmit and receive data. Thus, it is more manageable for processing purposes than multiple polarization radar. Respecting limits of on-board processing systems of radar platforms, therefore, much research has been concentrated in how to better process single polarization radar data to identify targets.
Unfortunately, currently developed single polarization radar processing techniques have yet to yield satisfactory results. For example, the Defense Advanced Research Projects Agency (DARPA) has set as a goal having a detection probability rate of 98 percent, while having a false alarm rate on the order of 0.001 false alarms per square kilometer. However, current automatic target detection systems using single polarization radar with adequate sensitivity generally have false alarm rates of 2 false alarms per square kilometer. This false alarm rate is orders of magnitude higher than is desired.
Multiple polarization radar has the potential to enhance automatic detection of targets. Multiple polarization radar transmits and receives signals in both vertical and horizontal planes. Thus, multiple polarization radar yields four sets of data. These sets include two forms of single polarization data: vertical transmit/receive data and horizontal transmit/receive data. These sets also include two forms of cross polarization data: vertical transmit/horizontal receive data and horizontal transmit/vertical receive data. Accounting for the varied alignment and resulting reflection of signals by differently oriented targets, multiple polarization radar can potentially detect targets that single polarization radar might not. The wealth of data returned by multiple polarization radar also demands greater processing resources.
In an attempt to exploit multiple polarization radar without exceeding available on-board processing capabilities, current multiple polarization radar automatic detection systems have attempted to limit their processing to one or more yielded parameters, such as radar cross section. Unfortunately, limiting the processing to a single quantity has not resulted in the type of automatic detection accuracy desired. Similarly, combinations of quantities researched to date also have failed to result in desired accuracy within the capabilities of available processing systems.
Thus, there is an unmet need in the art for an automatic target detection algorithm that takes advantage of the data provided by multiple polarization synthetic aperture radar to yield greater sensitivity and low false alarm rates.
The present invention provides a system, method, and computer-readable medium having instructions stored thereon for processing radar signals to more accurately identify targets of interest. From data yielded by multiple polarization radar, targets can be detected with improved accuracy using only two quantities which can be readily calculated from the multiple polarization radar data. These calculated quantities can be compared to an empirically derived table indicating which combinations of values of these quantities do and do not indicate the presence of a desired target.
An exemplary embodiment of the present invention detects targets in radar signals by first calculating, for a working point in a working radar data, a working total radar cross section and a working asymmetry angle from a working scattering matrix. The working total radar cross section and the working asymmetry angle are then evaluated to determine whether the working point should be classified as a target point or a clutter point.
In a preferred embodiment, the working total radar cross section and the working asymmetry angle for the working point are evaluated through the use of a look-up table. The look-up table associates combinations of a total radar cross section and an asymmetry angle representing target points and clutter points based on previously classified combinations of total radar cross sections and asymmetry angles. In addition, synthetic aperture multiple polarization radar is employed to collect basis and working data from both vertical and horizontal single polarization planar transmit and receive data, and one or both cross polarization data scans. A look-up table is created empirically from calculated combinations of total radar cross sections and asymmetry angles, eliminating suspected cultural clutter points as desired.