Communications – electrical: acoustic wave systems and devices – Echo systems – Side scanning or contour mapping sonar systems
Reexamination Certificate
2000-04-07
2001-10-30
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Echo systems
Side scanning or contour mapping sonar systems
Reexamination Certificate
active
06310830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to sonar apparatus and more particularly to a sonar system which adaptively modifies its vertical beamwidth and steering angle in accordance with the water depth in which it is operating so as to maximize the range at which detection and classification of underwater targets is possible.
2. Description of Related Art
The shift in emphasis from blue water to the littoral naval operations has increased the importance of capably detecting targets, such as mines, in shallow waters. However, detecting and classifying these targets, particularly mines in shallow water, is complicated by the proximity of the boundaries within which the target threat is found. In the case of Very Shallow Water (VSW), ranging from 10 feet to 40 feet water depth, the extreme proximity of the sea surface and bottom result in highly reverberant, multi-path environment with severe impact on the operation of conventional mine-hunting sonars, such as side looking sonars (SLS).
As sonar range potential increases due to technical advances such as Synthetic Aperture Sonar (SAS), the effect of boundary reverberation and multi-path is extended to deeper waters in the same way that the VSW affects state of the art sonar systems, i.e. as range is extended, deeper waters will tend to exhibit the same limitations as “shallow” water. Although particularly directed to VSW, the technique which will be disclosed hereinafter is also applicable to water depths that are substantially in excess of those found in the VSW environment. To regain a substantial measure of performance enjoyed in deeper water and to increase the search rate to acceptable levels, similar arrays must be modified to operate in this environment.
The basic problem associated with the VSW environment, or in water depths that are shallow with respect to sonar range, is depicted in FIG.
1
. As shown in
FIG. 1
, a side looking sonar (SLS)
10
is operating against a mine
12
residing on the bottom
14
of a body of water having a surface indicated by reference numeral
16
. Both the return sonar signal
18
and the acoustic shadow
20
behind it, where the mine body blocks the acoustic energy from hitting the bottom
14
, compete with multi-path
22
, and surface reverberation
24
arriving at the same time. Because both detection and classification rely on the target highlight and shadow so as to indicate both mine presence and dimension, operation is compromised.
Two possible methods to combat the adverse effects of the VSW environment include: (a) narrowing the vertical beamwidth to decrease the vulnerability to both multi-path and direct verberation; and (b) the placement of a dynamic null in the vertical beam pattern to counteract direct surface verberation. In the latter case, both the geometry of the situation and the sound velocity has to be known to enable the null to track the expected source point of the surface reverberation. In the multi-path environment, however, a null directed at the surface will not remove all the interfering paths. Accordingly, the approach chosen in the subject invention is to dynamically narrow the vertical beamwidth until sufficient gain is achieved against interference.
SUMMARY
Accordingly, it is an object of the present invention to provide an improved method and apparatus for detecting and classifying underwater targets.
It is a further object of the invention to provide an improved method and apparatus for detecting and classifying targets in shallow waters.
It is also an object of the present invention to provide an improved method and apparatus for detecting and classifying targets in water depths that are shallow with respect to sonar range.
And yet it is still another object of the invention to provide an improved method and apparatus for detecting and classifying underwater targets such as mines in both very shallow waters and in water depths that are shallow with respect to sonar range.
The foregoing and other objects of the invention are achieved in a sonar system by adaptively modifying the vertical beamwidth of the received beam of a sonar return signal as a function of water depth, altitude and range. The received beam is also vertically steered as a function of altitude and is steered at least once prior to the adaptive modification of the beamwidth. The received vertical beamwidth is made smaller as range increases by growing or enlarging the vertical aperture by increasing the number selected elements in the hydrophone array. This is achieved by dynamically controlling a vertical beamformer by controlling the number of elements selected and the vertical steering angle in response to sensors which provide, among other things, data as to water depth, altitude or sonar depth, platform dynamics, and sonar range/time.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the method and apparatus set forth in a detailed description are provided by way of illustration only, since various changes and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art.
REFERENCES:
patent: 3922634 (1975-11-01), Warner
Northtrop Grumman Corporation
Pihulic Daniel T.
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