Communications: directive radio wave systems and devices (e.g. – Clutter elimination
Patent
1999-07-20
2000-03-21
Sotomayor, John B.
Communications: directive radio wave systems and devices (e.g.,
Clutter elimination
162 91, 162 93, 162115, 162192, G01S 13534
Patent
active
060407972
DESCRIPTION:
BRIEF SUMMARY
The invention is based on a method of detecting a radar target, as defined in the preamble to claim 1.
The term "radar target" as used in this patent application is a synonym (abbreviation) for the expression "a target that can be detected by means of a radar system." "Target" refers to an object that reflects radar waves and possesses at least one predeterminable characteristic, for example, it exceeds a predeterminable minimal radar backscatter cross section.
The invention can be applied particularly to the detection of sea targets, such as ships, that are surrounded by possible so-called (radar) clutter caused by, for example, ocean waves and/or environmental influences such as clouds and/or precipitation.
In the detection of sea targets in particular, it is known to divide a region to be monitored into cells (measurement windows) having a predeterminable area. Each cell contains a predeterminable number of so-called radar resolution cells. It is obvious to first select at least one measurement window that contains only (possibly time-dependent) clutter, and to determine a so-called clutter threshold value (in the video signal) for this cell (in the video signal of the radar system) that is based on, for example, the formation of a clutter average value within the window. If a predeterminable (amplitude) pulse exceeds the clutter threshold value in the video signal, this pulse is first considered a possible echo of a radar target (sea target), and may be supplied to a further evaluation, such as a classification and/or identification, if needed.
It is apparent that, in the detection of sea targets, the associated clutter threshold value is dependent on both time and location. This is because the motion of water waves can change over time, for example due to an impending storm. Furthermore, the wave motion and therefore the clutter can vary by location, at least from the viewing direction of a radar system; for example, they may assume different values in the close and far ranges. Such conditions interfere with and impede the detection of sea targets in particular.
It is the object of the invention to improve a generic method so as to permit a reliable determination of a clutter threshold value, especially in the detection of sea targets.
This object is accomplished by the features disclosed in the characterizing portion of claim 1. Advantageous embodiments and/or modifications ensue from the further claims.
A first advantage of the invention is that the determination of the clutter threshold in a wide range is independent of (radar) targets located within the (measurement) window selected for determining the clutter threshold value. It is advantageously not necessary to extract the target amplitudes (in the video range) present in this (measurement) window, which amplitudes are associated with the (radar) targets, for example by reducing the (measurement) window and increasing the number to be evaluated. In other words, it is advantageously not necessary to know where (radar) targets are located within the (measurement) window, because an extraction is only possible with such (difficult-to-obtain) knowledge. It is advantageously possible to reliably determine the clutter threshold value even if the component of the target amplitudes assumes a value of about 50% of all amplitudes to be evaluated in a selected (measurement) window.
A second advantage is that the method is virtually independent of the design of the radar system, particularly the target extractor used in the system. The extractor generally includes a digital data-processing system that preferably has a programmable microprocessor. If, for example, the method of the invention is to be employed in an existing radar system, it is advantageously only necessary to change the program (software) of the data-processing system. Thus, no assemblies (hardware) need to be changed, which is also advantageous.
Further advantages ensue from the following description.
The invention is described in detail below by way of embodiments, with reference to schem
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Daimler-Chrysler AG
Kinberg Robert
Sotomayor John B.
Spencer George H.
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