Communications – electrical: acoustic wave systems and devices – Echo systems – Speed determination
Reexamination Certificate
1999-09-17
2001-05-08
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Echo systems
Speed determination
C367S089000, C367S090000
Reexamination Certificate
active
06229761
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to the determination of ship velocity, and more particularly to a method and system for estimating ship velocity through the water (i.e., relative to the water) and over the ground (i.e., relative to the ground).
(2) Description of the Prior Art
In shipboard active sonar systems, the change in received frequency (i.e., Doppler shift) based on relative speed of the ship is a critical issue when trying to differentiate moving targets from background (stationary) sources of reflection or reverberation. The Doppler shift in the echo from a stationary object is a function of the speed of the sonar's transmitter (i.e., ship velocity) through the water in the direction of the object. One device used to measure ship velocity is an electromagnetic velocimeter wherein a pitot tube is used to measure the speed of the ship in water. A change in pressure on the tip of the pitot tube is experienced due to the ship's speed in water which is measured by a corresponding change in its electrical resistance. However, this type of device is operationally unreliable, quickly drifts out of calibration and has a high error factor. Any errors in ship velocity lead to errors in Doppler compensation of the active sonar thereby degrading sonar and fire control performance.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method and system for accurately estimating own ship velocity through the water and over the ground.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, a method and system are provided to estimate a ship's velocity relative to the water and relative to the ground. A sonar system onboard a ship is operated to generate sonar returns. Two returns originating from two different directions are selected. Each return includes volume reverberation data and bottom reverberation data. A Doppler shift in frequency for each of the two returns based on the volume reverberation data is determined as a basis for estimating ship velocity relative to the water. A Doppler shift in frequency for each of the two returns based on the bottom reverberation data is determined as a basis for estimating ship velocity relative to the ground.
REFERENCES:
patent: 5050133 (1991-09-01), Buddery
patent: 2232488 (1990-12-01), None
D'Amelia Henry Ralph
D'Amelia Henry Robert
Korolenko Kyrill V.
Lall Prithvi C.
Lobo Ian J.
McGowan Michael J.
Oglo Michael F.
The United States of America as represented by the Secretary of
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