Systems and methods for bi-static or multi-static holographic navigation
The application relates to bi-static or multi-static holographic navigation systems, including methods of localizing an emitter or receiver with high precision relative to the sea floor. The system and methods can be used with a fully active sonar or radar system using well synchronized transmitters and receivers. The system and methods can be used with a passive sonar or radar system localizing a transmitter or a receiver based on poorly timed received signals.
1. A high frequency sonar system comprising a phase error corrector configured to:
receive a sonar image;
estimate a range varying phase error of the received sonar image;
determine that a variation in the range varying phase error across the received sonar image is greater than a first error threshold;
in response to determining that the variation in the range varying phase error across the received sonar image is greater than the first error threshold:
split the received sonar image into a plurality of sub-regions;
estimate, for each sub-region of the plurality of sub-regions, a respective range varying phase error;
determine, for a sub-region of the plurality of sub-regions, that a variation in the range varying phase error across a respective sub-region is less than a second error threshold;
in response to determining that the variation in the range varying phase error across the respective sub-region is less than the second error threshold, correct the sub-region to reduce the variation in the range varying phase error across the respective sub-region.
2. The system of claim 1 , wherein the received sonar image is a real aperture image.
3. The system of claim 2 , wherein the phase error corrector is further configured for modifying the real aperture image with grazing angle compensation.
4. The system of claim 2 , wherein the first error threshold is based on a maximum range of the real aperture image.
5. The system of claim 1 , wherein the received sonar image is a synthetic aperture image.
6. The system of claim 1 , wherein the sub-regions are of equal size.
7. The system of claim 1 , wherein the sub-regions are of varying size, and the variation in size is based on the range.
8. The system of claim 1 , wherein the first error threshold is the same as the second error threshold.
9. The system of claim 1 , wherein the sub-regions have constant altitude phase error or constant sound speed error.
10. The system of claim 1 , wherein the respective range varying phase error is substantially constant across the sub-region.
11. A method of correcting range varying phase errors, comprising:
receiving a sonar image;
estimating a range varying phase error of the received sonar image;
determining that a variation in the range varying phase error across the received sonar image is greater than a first error threshold;
in response to determining that the variation in the range varying phase error across the received sonar image is greater than the first error threshold:
splitting the received sonar image into a plurality of sub-regions;
estimating, for each sub-region of the plurality of sub-regions, a respective range varying phase error;
determining, for a sub-region of the plurality of sub-regions, that a variation in the range varying phase error across a respective sub-region is less than a second error threshold;
in response to determining that the variation in the range varying phase error across the respective sub-region is less than the second error threshold, correcting the sub-region to reduce the variation in the range varying phase error across the respective sub-region.
12. The method of claim 11 , wherein the received sonar image is a real aperture image.
13. The method of claim 12 , further comprising modifying the real aperture image with grazing angle compensation.
14. The method of claim 12 , wherein the first error threshold is based on a maximum range of the real aperture image.
15. The method of claim 11 , wherein the received sonar image is a synthetic aperture image.
16. The method of claim 11 , wherein the sub-regions are of equal size.
17. The method of claim 11 , wherein the sub-regions are of varying size, and the variation in size is based on the range.
18. The method of claim 11 , wherein the first error threshold is the same as the second error threshold.
19. The method of claim 11 , wherein the sub-regions have constant altitude phase error or constant sound speed error.
20. The method of claim 11 , wherein the respective range varying phase error is substantially constant across the sub-region.