Long-range acoustical positioning system on continental shelf regions
Methods and systems for determining a geophysical position of an object in an underwater channel are provided. Acoustic signals from at least two sources are received by a receiver of the object. The acoustic signals have a frequency corresponding to at least one waveguide mode associated with the underwater channel, where the acoustic signals are transmitted at predetermined transmission times. An arrival time for the at least one waveguide mode is determined from the received signals, based on the predetermined transmission times. The geophysical position is determined based on the arrival time and a modal group velocity for the at least one waveguide mode.
1. A method for determining a geophysical position of an object in an underwater channel, the method comprising:
receiving, by the object, acoustic signals from at least two sources, each received acoustic signal including one or more waveguide modes associated with the underwater channel excited by a frequency of the respective acoustic signal transmitted through the underwater channel, the acoustic signals being transmitted at respective predetermined transmission times;
identifying a waveguide mode among the one or more waveguide modes in the received acoustic signals;
determining a modal group velocity corresponding to the identified waveguide mode, based on a sound speed profile of each source and a frequency of the identified waveguide mode from the received acoustic signals;
determining an arrival time for the identified waveguide mode from the received acoustic signals, based on the respective predetermined transmission times; and
determining the geophysical position based on the arrival time of the identified waveguide mode and the modal group velocity for the identified waveguide mode.
2. The method according to claim 1 , further comprising determining the sound speed profile of each source.
3. The method according to claim 2 , wherein the sound speed profile of each source is determined as a function of temperature relative to depth of the underwater channel.
4. The method according to claim 3 , wherein the determining of the sound speed profile of each source includes:
measuring the sound speed profile of each source using a thermistor string in an operation area associated with the at least two sources.
5. The method according to claim 3 , wherein the determining of the sound speed profile of each source includes:
estimating the respective sound speed profile based on predetermined temperature values for an operation area associated with the at least two sources.
6. The method according to claim 1 , wherein the geophysical position of the object is determined relative to the at least two sources for a range of less than or equal to about 100 km.
7. A receiver disposed on an object in an underwater channel comprising:
a receiving element configured to receive acoustic signals from at least two sources, each received acoustic signal including one or more waveguide modes associated with the underwater channel excited by a frequency of the respective acoustic signal transmitted through the underwater channel, the acoustic signals being transmitted at respective predetermined transmission times; and
a processor configured to:
identify a waveguide mode among the one or more waveguide modes in the received acoustic signals;
determine a modal group velocity corresponding to the identified waveguide mode, based on a sound speed profile of each source and a frequency of the identified waveguide mode from the received acoustic signals;
determine an arrival time for the identified waveguide mode from the received acoustic signals, based on the respective predetermined transmission times, and
determine a geophysical position of the object based on the arrival time of the identified waveguide mode and the modal group velocity for the identified waveguide mode.
8. The receiver according to claim 7 , further comprising a clock synchronized with respective clocks of the at least two sources.
9. The receiver according to claim 7 , further comprising a memory for storing at least one of the predetermined transmission time for each source and modal group velocities for a plurality of waveguide modes.
10. The receiver according to claim 7 , further comprising a transmitting element for transmitting a further acoustic signal to a remote observer,
wherein the further acoustic signal and one or more of the acoustic signals from the respective at least two sources are received by the remote observer and used to determine the geophysical position of the object.
11. The receiver according to claim 7 , wherein the sound speed profile is a function of temperature relative to depth of the underwater channel.
12. The receiver according to claim 7 , further comprising a depth sensor for determining a depth of the object in the underwater channel.
13. The receiver according to claim 7 , wherein the geophysical position of the object is determined relative to the at least two sources for a range of less than or equal to about 100 km.
14. The receiver according to claim 7 , wherein the object includes an autonomous underwater vehicle (AUV).
15. An acoustical positioning system for an underwater channel comprising:
at least two sources configured to transmit acoustic signals, each acoustic signal including a frequency to excite one or more waveguide modes associated with the underwater channel, the acoustic signals being transmitted at respective predetermined transmission times; and
a receiver disposed on an object configured to receive the acoustic signals from the at least two sources, each received acoustic signal including the one or more waveguide modes excited via the respective source, the receiver including:
a processor configured to:
identify a waveguide mode among the one or more waveguide modes in the received acoustic signals;
determine a modal group velocity corresponding to the identified waveguide mode, based on a sound speed profile of each source and a frequency of the identified waveguide mode from the received acoustic signals;
determine an arrival time for the identified waveguide mode from the received acoustic signals, based on the respective predetermined transmission times; and
determine a geophysical position of the object based on the arrival time of the identified waveguide mode and the modal group velocity for the identified waveguide mode.
16. The system according to claim 15 , wherein each of the at least two sources and the receiver includes clocks synchronized with each other.
17. The system according to claim 15 , wherein each source includes a memory for storing at least one of the respective predetermined transmission time and the sound speed profile associated with the source.
18. The system according to claim 15 , wherein each source includes a further processor for determining the sound speed profile associated with the respective source, the sound speed profile being a function of a temperature relative to a depth of the underwater channel.
19. The system according to claim 18 , wherein the at least two sources are associated with at least one thermistor string, and, the further processor determines the sound speed profile for each source based on temperature values from the at least one thermistor string.
20. The system according to claim 18 , wherein the further processor determines the sound speed profile based on predetermined temperature values for an operation area associated with the at least two sources.
21. The system according to claim 18 , wherein:
the receiver includes a transmitting element for transmitting a further acoustic signal,
one or more of the at least two sources includes a receiving element for receiving the further acoustic signal and the acoustic signals from the remaining sources, and
the further processor determines the geophysical position of the object.
22. The system according to claim 15 , wherein one or more of the at least two sources includes an array of sources for transmitting respective acoustic signals.
23. The system according to claim 15 , wherein the frequency corresponding to the at least one waveguide mode is less than or equal to about 500 Hz.
24. The system according to claim 15 , wherein each source transmits the respective acoustic signal at a same time.
25. The system according to claim 15 , wherein one or more of the at least two sources transmits the respective acoustic signal at a different time.
26. The system according to claim 15 , wherein one or more of the at least two sources transmits the respective acoustic signal with a further frequency corresponding to a different waveguide mode.