Communications: directive radio wave systems and devices (e.g. – Determining direction – Low angle processing
Reexamination Certificate
2000-05-19
2002-06-04
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining direction
Low angle processing
C342S02600R, C342S027000, C342S175000, C342S195000
Reexamination Certificate
active
06400312
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a method of object detection and a device implementing the method, for example detection of the presence or non-presence of an aircraft, specifically the detention of low flying aircraft below the radar horizon.
BACKGROUND
The present invention generally relates to a method of Conventional radio frequency (r.f.) radar systems have been used to detect aircraft for a couple of decades. During this time different sophisticated methods have evolved to gather better and more information about detected aircraft, one such method is Doppler radar systems that can differentiate between ground clutter and a moving target Even with these advances, conventional radar systems possess certain natural limitations in the detection of low flying aircraft, especially aircraft or other objects of interest below the radar horizon There have been attempts to overcome these limitations by the use of acoustic detection methods. Such a system is described in U.S. Pat. No. 4,630,246. The system according to U.S. Pat. No. 4,530,246 relies on the use of microphones and seismic detectors to detect low flying aircraft. It can be considered a disadvantage that in order to cover a large detection area it is necessary to have to scatter a multitude of microphones and seismic detectors over the area in question.
There seems to be room for improvement in the manner of detecting low flying aircraft and other objects of interest.
SUMMARY
An object of the invention is to define a method and a device for efficiently detecting objects of interest which are below the radar horizon.
Another object of the invention is to define a method and a device, which is able to identify different objects of interest, which are below the radar horizon.
The aforementioned objects are achieved according to the invention by a method of detecting objects of interest, which are below the radar horizon. The method according to the invention can only detect objects of interest that emit or are the cause of pressure wave fronts. By emitting radar pulses that interact with the pressure wave fronts that appear above the radar horizon and then by analysis of the detected echo signals in the range bins, the existence of one or more pressure wave fronts can be determined. Thereafter it is evaluated if this or these pressure wave fronts indicate the presence of an object of interest or not. The transmitted radar pulses in relation to the detected echoes can be used for identifying the object of interest. The emitted radar pulses preferably have a wavelength, which is a multiple of the expected wavelength of the pressure wave fronts.
The aforementioned objects are also achieved by a method of detecting objects of interest, which are below the radar horizon. The method utilizes the expected presence of pressure wave fronts above the radar horizon, which pressure wave fronts are emitted from or are caused by the object of interest. The method comprises a number of steps. In a first step radar pulses are emitted in the estimated direction of the object of interest. Preferably the radar pulses are emitted into a volume where there is believed to be no physical objects, so that any returned echoes are not from bouncing of an object but due to an interaction with a pressure wave front. In a second step echoes from the estimated direction of the object of interest are detected. In a third step the existence of pressure wave fronts in the estimated direction of the object of interest are evaluated, in dependence of the detected echoes having interacted with pressure wave fronts. In a fourth step the presence of an object of interest below the radar horizon is evaluated in dependence on the evaluation of the existence of pressure wave fronts above the radar horizon.
The emitted radar pulses preferably have a wavelength being substantially a multiple of, and in some embodiments twice, the wavelength of the expected pressure wave frosts above the radar horizon. The emitted radar pulses can preferably either hare a fixed wavelength or have a wavelength that varies in the vicinity of a wavelength being a multiple of the wavelength or wavelengths of the expected pressure wave fronts above the radar horizon.
Advantageously in the step of evaluating the existence of pressure wave fronts, either only bins representing distances in the approximate range of the object of interest are used, only bins representing distances divergent from but in the approximate range of the object of interest are used, only bins representing distances corresponding to the radar horizon are used, or a suitable mix of the above, for example during different stages in the evaluation. The bins used can in some embodiments preferably be predetermined.
Advantageously the step of evaluating the existence of pressure wave fronts comprises a number of existence substeps. In a first existence substep a probability that there are pressure wave fronts is determined based on received echoes and their spread and magnitude in the bins. In a second existence substep it is determined if the probability is larger than a predetermined pressure wave front threshold value, and if it is determined that the probability is larger than the predetermined pressure wave front threshold value then it is evaluated that there are pressure wave fronts.
Further in some versions the step of evaluating the presence of an object of interest comprises a number of presence substeps. In a first presence substep a probability that there is an object of interest is determined based on the evaluation of the existence of pressure wave fronts, In a second presence substep it is determined if the probability is larger than a predetermined object threshold value, and if it is determined that the probability is larger than the predetermined object threshold value then it is evaluated that there is an object of interest below the radar horizon.
Advantageously the method further comprises the step of identifying the object of interest by analysis of the transmitted radar pulses in relation to the detected echoes.
One or more of the features of the above-described different methods according to the invention can be combined in any desired manner, as long as the features are not contradictory.
The aforementioned objects are also achieved according to the invention by a radar system arranged to detect an object of interest below the radar horizon. The radar system utilizes the expected presence of pressure wave fronts above the radar horizon, which pressure wave fronts are emitted from or caused by the object of interest. The radar system comprises a radar pulse transmitter, a radar pulse receiver, a signal processor and an evaluator. The radar pulse transmitter emits radar pulses in the estimated direction of the object of interest. Preferably the radar pulses are emitted into a volume where there is believed to be no physical objects, so that any returned echoes are not from bouncing of an object but due to an interaction with a pressure wave front. The radar pulse receiver detects echoes from the estimated direction of the object of interest. The signal processor evaluates the existence of pressure wave fronts in the estimated direction of the object of interest, in dependence of the detected echoes having interacted with pressure wave fronts. The evaluator evaluates the presence of an object of interest below the radar horizon in dependence on the signal processor's evaluation of the existence of pressure wave fronts above the radar horizon.
Preferably the radar pulse transmitter emits radar pulses having a wavelength being substantially a multiple of, and in some embodiments twice, the wavelength of the expected pressure wave fronts above the radar horizon. The radar pulse transmitter advantageously emits radar pulses having either a fixed wavelength, or a wavelength that varies in the vicinity of a wavelength being a multiple of the wavelengths or wavelengths of the expected pressure wave fronts above the radar horizon.
The signal processor in evaluating the exis
Burns Doane Swecker & Mathis L.L.P.
Gregory Bernarr E.
Telefonaktiebolaget LM Ericsson (publ)
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