SYSTEM AND METHOD FOR DETERMINING THE POSITION OF AN UNDERWATER VEHICLE

• US 20090216444A1
• Filed: 02/15/2007
• Published: 08/27/2009
• Est. Priority Date: 02/23/2006
• Status: Active Grant

• Current Assignee: L3 Technologies, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: Ocean Farm Technologies Inc. (Baja Aquaculture, Inc.)
• Inventors: Crowell, Jonathan C.
• Granted Patent: US 9,223,002 B2
• Time in Patent Office: Days
• US Class Current: 701/213
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: G01S 2013/466 by Trilateration, i.e. two antennas or two sensors determine separately the distance to a target, whereby with the knowledge of the baseline length, i.e. the distance between the antennas or sensors, the position data of the target is determined
• CPC Class Codes: G01S 5/0045 Transmission from base station to mobile station G01S5/009 takes precedence
• CPC Class Codes: G01S 5/0284 Relative positioning

Abstract

A system and a method are provided for determining the position of an underwater vehicle while the vehicle is operating underwater. A buoyant float stays on or near the surface of the water and is attached to the vehicle by thin tether that can include insulated wires. The vehicle moves under the water and pulls the float behind it. The float can receive a localization signal, such as a signal indicating its GPS position, and so can determine its position precisely. The position can be transmitted to the underwater vehicle over the wires located in the tether. The underwater vehicle can use sensors and/or calculations to determine the positional offset of the vehicle from the float buoy and generates its true position based on the known position of the float and the positional offset. The float can be constructed with attributes that will allow the float it operate with a greater tether length, and in turn allow the underwater vehicle to operate at greater depths. The float may also generally carry a radio system for high speed communication of signals from the vehicle while the vehicle is submerged.

Claims

1. A system for determining the position of an underwater vehicle comprising:

a float, the float including a receiver for receiving a position signal representing the position of float and the float being sufficiently buoyant so as to place the receiver in a position to receive the signal;

a tether connecting the float to the underwater vehicle and providing a communication channel between the float and the underwater vehicle; and

an offset calculation element provided on at least one of the float and the underwater vehicle to provide a position offset distance between the underwater vehicle and the float;

wherein the position offset distance is added to the position of the float to result in a position of the underwater vehicle.

2. The system of claim 1, wherein the offset calculation element includes a range finding element for sending a signal through the water between the float and the underwater vehicle and a processor configured to determine the time it takes for the signal to pass between the float and the underwater vehicle and to calculate the distance between the float and the underwater vehicle using the speed of the signal in water and the determined time.

3. The system of claim 2, wherein the range finding element is an acoustic transmitter.

4. The system of claim 2, wherein the range finding element is configured to provide a pulse of light of a wavelength suited for travel through water.

5. The system of claim 2, wherein the offset calculation element further includes a depth sensor for determining a depth of the underwater vehicle.

6. The system of claim 5, wherein the processor solves for the position offset distance using the depth of the underwater vehicle and the distance between the float and the underwater vehicle.

7. The system of claim 6, wherein the position offset distance is determined in a direction of travel of the underwater vehicle and in a direction perpendicular to the direction of travel of the underwater vehicle.

8. The system of claim 1, wherein the tether includes a fiber optic communication channel.

9. The system of claim 1, wherein the receiver is a GPS receiver.

10. The system of claim 1, wherein the tether length in the water is adjustable during operation by a motor and control system based on the depth of the vehicle and its speed.

11. The system of claim 1, wherein the float buoy is both hydrodynamic and smoothly shaped so that it can be pulled through obstacles without catching.

12. The system of claim 1, wherein the float buoy as a propulsion device that pushes the float based on sensing the tension between the tether and the float.

13. A method for determining the position of an underwater vehicle, comprising:

providing a float having a receiver tethered to the underwater vehicle;

receiving on the receiver a signal representative of a position of the float;

calculating a position offset distance between the float and the underwater vehicle; and

adding the position offset distance to the position of the float to determine the position of the underwater vehicle.

14. The method of claim 13, wherein calculating the position offset distance includes:

determining a distance between the float and the underwater vehicle;

determining the depth of the underwater vehicle; and

solving for the position offset distance.

15. The method of claim 13, wherein the position offset distance is determined in a direction of travel of the underwater vehicle and in a direction perpendicular to the direction of travel of the underwater vehicle.

24. The system of claim 13, wherein the angle of the float is measured to increase the accuracy of the fix offset.

16. A system for accurately determining the position of a vehicle located under the surface of a body of water, comprising:

a. a buoyant float having a GPS receiver with an antenna disposed above the surface of the water;

b. a tether having a communication channel that is connected between the underwater vehicle and the float;

c. a range finder for measuring the distance between the float and vehicle;

d. a heading sensor for determining a heading for the underwater vehicle; and

e. a processor for generating an offset for addition to a GPS fix obtained for the float to represent the location of the underwater vehicle.

17. The system of claim 16, wherein the range finder is an acoustic range finder provided on at least one of the float and the vehicle.

18. The system of claim 16, wherein the range finder is a light based range finder provided on at least one of the float and the vehicle.

19. The system of claim 16, wherein the distance measurement is performed using acoustic ranging between the float buoy and vehicle wherein an acoustic transmitter on the float transmits a signal to an acoustic receiver on the vehicle and calculates the distance between the two and the synchronization of the transmit pulse is achieved by signaling through the tether.

20. The system of claim 16, wherein the tether comprises a fiber optic cable.

21. The system of claim 16, wherein the tether cable has added buoyancy so that its weight in water is controlled to lighten the downward pull on the float.

22. The system of claim 16, wherein the distance between the devices is calculated based on knowing the amount of tether that is un-reeled and the speed of the vehicle.

23. The system of claim 22, wherein the distance is calculated using a table based experimental data measured.