Multiplatform sonar system and method for underwater surveillance

• US 5,231,609 A
• Filed: 09/28/1992
• Issued: 07/27/1993
• Est. Priority Date: 09/28/1992
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Gaer, Marvin C.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US07/952,380
• Time in Patent Office: 302 Days
• Field of Search: 367/99, 367/118, 367/136, 367/117
• US Class Current: 367/99
• CPC Class Codes: G01S 15/00 Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
• CPC Class Codes: G01S 15/003 Bistatic sonar systems; Multistatic sonar systems
• CPC Class Codes: G01S 15/872 Combination of several systems for attitude determination using inertial means G01C9/00, control of attitude G05D1/49

Abstract

A system and method of indirect underwater acoustic ocean surveillance is sclosed requiring at least two sonar platforms, usually ships, travelling some distance apart. At least one of the platforms transmits sonar pulses, portions of which are scattered off the ocean floor to at least one companion sonar receiver platform. The receiver platform is provided with means to analyze the received scattered sonic pulses to determine if a submerged object such as a submarine is obstructing a portion of the pulse, thus casting an acoustic shadow. With accurate positioning information supplied by a navigation information system such as the NAVSTAR GLOBAL POSITIONING SYSTEM (GPS), and by combining pulse measurements over several positions the system will be able to locate, identify, and track the obstructing object by analyzing these acoustic shadows or silhouettes. Geometric silhouette reconstruction techniques and other mathematical techniques may be employed to construct an image of the submerged object.

Claims

1. A system for underwater surveillance of the ocean through the transmission and reception of underwater sonic pulses, said system comprising at least two platforms positions or travelling some distance apart from each other, wherein at least one of said platforms is equipped with means for transmitting underwater sonic pulses and scattering them off the ocean floor in directions such that portions of the scattered pulses are intercepted by at least one of said transmitting platform'"'"'s companion platforms in the absence of submerged sonic obstructing objects, means on at least one of said platforms for receiving said sonic pulses and determining the angles of arrival of said intercepted pulses, means on each of said reception platforms for determining the times of transmission and the times of reception of said conic pulses, means on each of said reception platforms for sensing acoustic shadows cast by submerged sonic obstructing objects, position fixing means on each moveable platform for determining its global location;

said system having a relative position fixing means for determining the positions of said platforms with respect to each other, communication means on each platform for transmitting and receiving data from its companion platforms;

said system having means for recording, processing, and analyzing portions of said intercepted pulses to estimate the depth of the ocean floor at the locations of the pulse reflections, and means for estimating the directions, distances, boundaries, and dimensions of the sonic obstructing objects casting said acoustic shadows, and said system having means for recording selected portions of said analyzed data.

2. The system of claim 1, wherein said platforms are ships.

3. The system of claim 1, wherein at least one of said platforms has a means for determining and directing the course, velocity, and sonic pulsing of each of its moveable companion platforms.

4. The system of claim 1, wherein said means for transmitting said sonic pulses are sonar projector arrays.

5. The system of claim 1, wherein said means for receiving said sonic pulses are sonar hydrophone arrays.

6. The system of claim 1, wherein said position fixing means on each of said platforms for determining its absolute location, and said relative position fixing means of said system for determining the relative positions of said platforms with respect to each other, are the apparatus and receivers associated with a space satellite positioning system.

7. The system of claim 6, wherein said space satellite positioning system is the NAVSTAR GLOBAL POSITIONING SYSTEM.

8. The system of claim 1, further comprising a remote data processing facility for processing the obtained data and directing the surveillance operation;

said system further comprising means for rapid remote communication and data transfer between system elements.

9. A method for underwater surveillance of the ocean through the transmission and reception of underwater sonic pulses, comprising the steps of providing a system of sonar transmitting and receiving platforms having at least one platform equipped with means for transmitting underwater sonic pulses in a direction such that portions of said pulses are scattered off the ocean floor to at least one companion receiver platform located or travelling some distance from said transmitter platforms;

said receiver platforms being kept sufficiently close to said transmitter platforms to be able to intercept portions of said scattered pulses;

said receiver platforms being equipped with sonic receiver equipment, having said receiver platforms intercept portions of said scattered sonic pulses not obstructed by submerged sonic obstructing objects;

said receiver platforms being provided with means for processing and analyzing said received pulses, providing each of said platforms with a data transmission and reception communication system, providing position fixing data to said platforms enabling each of said platforms to determine its global location and its relative position with respect to its companion platforms, providing each of said platforms with the times of transmission of said pulses, having each of said platforms determine the times it intercepts portions of said pulses, having each of said platforms determine the angles of arrival of portions of said intercepted scattered sonic pulses, having said system record said angles of arrival, position and time data of said received portions of said pulses, having the system process and analyze said intercepted pulses to estimate the depths of the ocean at the locations of the pulse reflections, having said system analyze said intercepted pulses to estimate the directions, locations, boundaries and dimensions of the acoustic shadows cast by submerged sonic obstructing objects which may be encountered by said scattered sonic pulses and having said system record selected portions of this analyzed data.

10. The method of claim 9, further comprising the step of designating one of the platforms as the controlling or master platform, this platform to determine the courses and velocities of its companion platforms and also to determine the timing of the transmission of said sonic pulses, their directions and their shapes.

11. The method of claim 9, further comprising the steps of estimating the locations, boundaries, and dimensions of said sonic obstructing objects by estimating the position of closest mutual approach of rays geometrically projected from at least two receiver reference positions through the centroids of said acoustic shadows in the direction of said shadows, said location of closest mutual approach of said rays being used to estimate the true scale of the distance, location, and dimensions of said boundaries of said sonic obstructions.

12. The method of claim 11, further comprising the steps of estimating the identity of said sonic obstructing object by synthesizing a three-dimensional image of said object using silhouette reconstruction techniques and comparing said image with the images of known objects.

13. The method of claim 11, further comprising the step of tracking said sonic obstructions by computing changes in position of said locations of closest approach over several of said sonic pulses.

14. The method of claim 9, wherein each set of sonic pulses from a particular transmitting platform is transmitted at a different frequency from the set of sonic pulses transmitted from each of the other of said transmitting platforms.

15. The method of claim 9, wherein the position fixing data is provided by a spaced satellite positioning system.

16. The method of claim 15, wherein said space satellite positioning system is the NAVSTAR GLOBAL POSITIONING SYSTEM.

17. The method of claim 9, further comprising the steps of providing a remote data processing facility for processing the obtained data and directing said surveillance operation, providing rapid remote communication and data transfer means between system elements, transferring said data from said platforms to said remote processing facility, processing said data at said remote facility, incorporating said data processing results in said remote facility'"'"'s surveillance operation directions, and having said remote processing facility communicate said data processing results and surveillance operation directions to said platforms.