Communications – electrical: acoustic wave systems and devices – Underwater system – Telemetering
Reexamination Certificate
1999-09-17
2001-04-10
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Underwater system
Telemetering
C367S902000
Reexamination Certificate
active
06215732
ABSTRACT:
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a system and method for measuring a sound velocity profile in a medium and particularly, to a system and method that uses an expendable vehicle to measure a sound velocity profile in a body of water surrounding a submarine or other water vessel.
(2) Description of the Prior Art
Underwater sonic equipment has many uses including, for example, fish and depth finding as well as sophisticated ranging and navigating. This equipment typically transmits a sonic signal from an underwater vessel, such as a submarine, and detects the return of an echo signal. Calculations based upon the elapse of time between the transmission of a sonic signal and the return of an echo makes it possible to ascertain the distance between the sonic transmitter and the object reflecting the sonic energy. Thus, knowledge of the sound velocity in the water between the submarine and the target is important to accurately interpret the acoustic data received from the sonar.
The sound velocity in water varies with localized conditions, such as water temperature, density, depth, salinity, and other factors. The sound velocity should therefore be measured at numerous points between the submarine or other such vessel and the target in order to obtain an accurate sound velocity profile. The present devices and techniques for measuring sound velocity, however, have a number of disadvantages.
One technique includes determining the velocity of sound by measuring the water temperature, salinity and other factors at given depths and then empirically finding the velocity using charts, tables and other data. These techniques are inherently inaccurate and time consuming. Another limitation is that the sound velocity can only be determined in those regions in which the temperature and other conditions can be measured.
Attempts have been made to measure the velocity directly within the medium itself, for example, using unmanned underwater vehicles (UUVs). Although the sound can be measured directly at locations remote from the submarine or other such vessel, the existing devices typically used to provide this direct measurement, e.g., conductivity-temperature-depth measuring devices (CDT), are expensive and require a relatively large, expensive vehicle for deployment. These devices must also be connected to the submarine or vessel using a fiber optic cable to relay the measured data back to the submarine. Because of the expensive equipment used in the UUV, the UUV must be recovered at the completion of its mission, a potentially dangerous and time consuming undertaking under combat conditions. Moreover, the submarine or other deployment vessel must be modified to allow it to recover the UUV.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is a system and method for measuring a sound velocity profile within a medium, such as a body of water, at a relatively wide range of locations.
Another object of the present invention is a system and method for measuring the sound velocity profile in a medium that uses an expendable device that does not have to be physically connected to the submarine or vessel and does not have to be recovered.
A further object of the present invention is to measure the sound velocity profile in a body of water around a submarine or vessel in a covert manner.
The present invention features a system and method for measuring sound velocity in a medium, such as a body of water. The system comprises an acoustic signal transmitting system disposed at a transmitting location in the medium for transmitting one or more acoustic signals through the medium at a predetermined transmission time. An acoustic signal receiving and processing system is disposed at a receiving location remote from the transmitting location for receiving the acoustic signal at an arrival time. The acoustic signal receiving and processing system processes the acoustic signal to determine a sound velocity in the medium between the transmitting location and the receiving location based upon the predetermined transmission time, the arrival time, and a distance between the transmitting location and the receiving location.
In the preferred embodiment, the acoustic signal transmitting system includes a first precision clock, and the acoustic signal receiving and processing system includes a second precision clock substantially synchronized with the first precision clock. The acoustic signal transmitting system preferably includes a controller, responsive to the first precision clock, for controlling transmission of the acoustic signal at the predetermined transmission time, and a transmitter, responsive to the controller, for transmitting the acoustic signal.
The acoustic signal receiving and processing system preferably includes a receiver, for receiving the acoustic signal at the arrival time, an acoustic processor, responsive to the receiver and the second precision clock, for processing the acoustic signal and for determining the arrival time of the acoustic signal, and a calculator, responsive to the acoustic processor, for determining the sound velocity in the medium between the transmitting location and the receiving location based upon the predetermined transmission time, the arrival time, and the distance between the transmitting location and the receiving location.
In one example, the acoustic signal transmitting system is disposed on an expendable underwater vessel, and the acoustic signal receiving and processing system is disposed on a submarine.
The method of measuring the sound velocity in the medium comprises the steps of predetermining at least one predetermined transmitting location and at least one predetermined transmission time for transmitting at least one acoustic signal from an acoustic signal transmitting system, transmitting the acoustic signal at the predetermined transmission time through the medium from the acoustic signal transmitting system at the transmitting location, receiving the acoustic signal at an arrival time in an acoustic signal receiving system at a receiving location remote from the predetermined transmitting location, and calculating a sound velocity in the medium between the transmitting location and the receiving location using the arrival time, the predetermined transmission time, and a distance between the predetermined transmitting location and the receiving location. The calculating is performed by the acoustic signal receiving and processing system at the receiving location.
The preferred method includes predetermining a plurality of predetermined transmitting locations and predetermined transmission times. The sound velocity in the medium between each of the transmitting locations and receiving locations form a sound velocity profile. The acoustic signals can be transmitted at a single frequency or in a range of frequencies. The frequency of each acoustic signal can also be varied with time.
REFERENCES:
patent: 3611276 (1971-10-01), Massa
patent: 4093934 (1978-06-01), Urick et al.
Lall Prithvi C.
McGowan Michael J.
Oglo Michael F.
Pihulic Daniel T.
The United States of America as represented by the Secretary of
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