Method and apparatus for fault-tolerant, correlation SONAR processing
A system is disclosed that enables the use of an incomplete SONAR array matrix in a correlation SONAR system. An improvement is achieved through the generation of a correlation-array model matrix of hydrophone correlations, based on an independent estimate of the ship's velocity, such as from an inertial navigator. Meanwhile, estimates of the missing values are generated based on one or more values from the model matrix, an interpolation of values from the SONAR array matrix itself, or some combination thereof. Regardless of how the missing values are generated, the model matrix provides a basis for comparison with the SONAR array matrix, which is populated with the estimated values, wherein subsequent comparisons are made between successive iterations of the model matrix and the SONAR array matrix. By applying the disclosed technique, a correlation SONAR system with incomplete data is able to continue working, and in the presence of a greater number of hydrophone failures than before.
1. A method for fault-tolerant processing for a correlation SONAR system, the method comprising:
receiving a first velocity estimate;
generating a first correlation-array model that comprises a first plurality of estimated correlation products that are based on i) the first velocity estimate and ii) the relative positioning of receivers within a plurality of receivers;
generating a correlation array that comprises a plurality of actual correlation products that are based on SONAR signals that are received by the receivers; and
developing a second velocity estimate, based on a difference between i) the first correlation-array model and ii) the correlation array.
2. The method of claim 1 wherein correlation array further comprises one or more substitute array elements that are based on at least one estimated correlation product from the first plurality of estimated correlation products.
3. The method of claim 2 wherein the elements in the correlation array correspond to a plurality of velocity-vector positions defined by receiver pairs within the plurality of receivers, and wherein the velocity-vector position at which a substitute array element is used is based on a receiver that has failed.
4. The method of claim 3 further comprising:
generating a revised correlation-array model that comprises a second plurality of estimated correlation products that are based on the second velocity estimate;
updating the correlation array with at least one estimated correlation product from the second plurality of estimated correlation products; and
developing a third velocity estimate, based on a difference between i) the revised correlation-array model and ii) the correlation array that comprises the second correlation product.
5. The method of claim 2 wherein the one or more substitute array elements are also based on an interpolation that involves at least one actual correlation product from the plurality of actual correlation products.
6. The method of claim 1 wherein the first velocity estimate is received from an initial navigator.
7. A method for fault-tolerant processing for a correlation SONAR system, the method comprising:
detecting that a receiver within a plurality of receivers has failed;
generating, based on the detection, a first correlation-array model that comprises a first estimated correlation product that is based on i) a first velocity estimate that has been developed independently of the correlation SONAR system and ii) the relative positioning of receivers within the plurality of receivers;
generating a correlation array that comprises i) at least one actual correlation product that is based on SONAR signals that are received by the receivers and ii) a substitute array element that is based on the first estimated correlation product; and
developing a second velocity estimate, based on a difference between i) the first correlation-array model and ii) the correlation array.
8. The method of claim 7 further comprising:
generating a revised correlation-array model that comprises a second estimated correlation product that is based on the second velocity estimate;
updating the correlation array with the second estimated correlation product; and
developing a third velocity estimate, based on a difference between i) the revised correlation-array model and ii) the correlation array that comprises the second correlation product.
9. The method of claim 7 further comprising receiving the first velocity estimate prior to the generation of the first correlation-array model.
10. The method of claim 9 wherein the first velocity estimate is received from an initial navigator.
11. The method of claim 7 wherein the elements in the correlation array correspond to a plurality of velocity-vector positions defined by receiver pairs within the plurality of receivers, and wherein the velocity-vector position at which the substitute array element is used is based on the receiver that has failed.
12. The method of claim 11 wherein the receiver that has failed is a back-up hydrophone.
13. The method of claim 7 wherein the substitute array element is also based on an interpolation that involves the at least one actual correlation product.
14. An apparatus comprising:
a receiver array that comprises a plurality of hydrophones;
means for developing a first velocity estimate independently of the plurality of hydrophones;
means for generating
a) a first correlation-array model that comprises a first estimated correlation product that is based on i) the first velocity estimate and ii) the relative positioning of the hydrophones, and
b) a correlation array that comprises i) at least one actual correlation product that is based on SONAR signals that are received by the hydrophones and ii) a substitute array element that is based on the first estimated correlation product; and
means for developing a second velocity estimate, based on a first difference between i) the first correlation-array model and ii) the correlation array.
15. The apparatus of claim 14 further comprising a transmitter that transmits a series of pulses.
16. The apparatus of claim 15 wherein the receiver array is a planar array of sixteen hydrophones for receiving echoes that are based on the transmitted series of pulses.
17. The apparatus of claim 16 further comprising means for detecting that a hydrophone has failed within the planar array, wherein the generation of the first correlation-array model is based on the detection.
18. The apparatus of claim 17 wherein the elements in the correlation array correspond to a plurality of velocity-vector positions defined by pairs of hydrophones in the planar array, and wherein the velocity-vector position at which the substitute array element is used is based on the hydrophone that has failed.
19. The apparatus of claim 18 wherein the planar array comprises prime hydrophones and back-up hydrophones, and wherein the hydrophone that has failed is a back-up hydrophone.
20. The apparatus of claim 14 further comprising means for performing an interpolation that involves the at least one actual correlation product, wherein the substitute array element is also based on the interpolation.