WIDEBAND SONAR RECEIVER AND SONAR SIGNAL PROCESSING ALGORITHMS

• US 20140286131A1
• Filed: 04/24/2014
• Published: 09/25/2014
• Est. Priority Date: 10/26/2011
• Status: Active Grant

• Current Assignee: Teledyne FLIR LLC (Teledyne Technologies Incorporated)
• Original Assignee: FLIR Systems, Inc. (Teledyne Technologies Incorporated)
• Inventors: Stokes, Paul, Webb, Phil
• Granted Patent: US 9,470,779 B2
• Time in Patent Office: Days
• US Class Current: 367/87
• CPC Class Codes: G01S 15/02 using reflection of acoustic waves G01S15/66 takes precedence
• CPC Class Codes: G01S 15/104 wherein the transmitted pulses use a frequency- or phase-modulated carrier wave
• CPC Class Codes: G01S 15/105 using irregular pulse repetition frequency
• CPC Class Codes: G01S 15/108 using more than one pulse per sonar period
• CPC Class Codes: G01S 15/14 wherein a voltage or current pulse is initiated and terminated in accordance respectively with the pulse transmission and echo reception
• CPC Class Codes: G01S 15/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 15/50 Systems of measurement, based on relative movement of the target
• CPC Class Codes: G01S 15/582 using transmission of interrupted pulse-modulated waves and based upon the Doppler effect resulting from movement of targets
• CPC Class Codes: G01S 15/96 for locating fish
• CPC Class Codes: G01S 7/52 of systems according to group G01S15/00
• CPC Class Codes: G01S 7/52001 Auxiliary means for detecting or identifying sonar signals or the like, e.g. sonar jamming signals
• CPC Class Codes: G01S 7/526 Receivers
• CPC Class Codes: G01S 7/527 Extracting wanted echo signals Doppler systems G01S15/50
• CPC Class Codes: G01S 7/5273 using digital techniques
• CPC Class Codes: G01S 7/5276 using analogue techniques

Abstract

A wideband sonar receiver is provided that includes: a selectable bandpass filter adapted to filter a received sonar signal to produce a filtered signal and a correlator adapted to correlate the baseband samples with baseband replica samples to provide a correlated signal. In addition, the wideband sonar receiver may include a shaping filter to shape unshaped received pulses. Finally, a variety of sonar processing algorithms are described with regard to reducing clutter and interference, target detection, and bottom detection.

Claims

1. A wideband sonar receiver, comprising:

a selectable bandpass filter adapted to filter a received sonar signal to produce a filtered signal;

an analog-to-digital converter for converting a version of the filtered signal to provide digitized samples;

a digital basebanding and decimation stage adapted to baseband and decimate the digitized samples to produce baseband samples of the received sonar signal; and

a correlator adapted to correlate the baseband samples with baseband replica samples to provide a correlated signal.

2. The wideband sonar receiver of claim 1, further comprising:

a variable gain amplifier adapted to apply a time-varying gain to the filtered signal from the selectable bandpass filter to produce a variable-gain-amplified version of the filtered signal to provide to the analog-to-digital converter as the version of the filtered signal.

3. The wideband sonar receiver of claim 1, wherein the correlator is a variable-length correlator.

4. The wideband sonar receiver of claim 1, wherein the received sonar signal is a frequency-modulated signal, and wherein the wideband sonar receiver further comprises:

a complex-to-magnitude stage configured to receive the correlated signal and extract a power of complex correlation results of the correlated signal; and

a logarithm stage configured to provide a detected echo signal output based on the extracted power of the complex correlation results.

5. The wideband sonar receiver of claim 4, wherein the analog-to-digital converter converts according to a subharmonic sampling rate.

6. The wideband sonar receiver of claim 4, wherein the analog-to-digital converter converts according to a rate of four times a center frequency for the frequency-modulated signal.

7. A method of processing a received wideband sonar signal, the method comprising:

selecting from a plurality of filter bands based upon a center frequency for the received wideband sonar signal;

filtering the received wideband sonar signal using the selected filter band; and

applying a time-varying gain to a resulting filtered signal.

8. The method of claim 7, further comprising digitizing a version of the resulting filtered signal to produce digitized samples.

9. The method of claim 8, wherein the digitizing occurs according to a subharmonic sampling rate.

10. The method of claim 9, wherein the digitizing occurs according to a rate of four times a center frequency for the received wideband sonar signal.

11. The method of claim 10, further comprising:

generating digital samples of a complex local oscillator signal;

multiplying the digital samples from the complex local oscillator signal with the digitized samples to produce mixed samples; and

low pass filtering the mixed samples to produce basebanded samples.

12. A sonar system for shaping a received sonar chirp pulse according to a shaped replica pulse, comprising:

a digital signal processor (DSP) configured to divide a frequency-domain version of the received sonar chirp pulse by a frequency-domain version of the shaped replica pulse (FSRP) to provide a shaping filter response and to multiply the shaping filter response by a conjugate of the FSRP to provide a combined correlation and shaping response, the DSP being further configured to multiply the frequency-domain version with the correlation and shaping response to produce a correlated and shaped signal.

13. The sonar system of claim 12, wherein the DSP is further configured to limit an extent of the correlation and shaping response to be no more than three times an extent of the FSRP.

14. The sonar system of claim 12, wherein the DSP is thither configured to limit an extent of the correlation and shaping response to be no more than two times an extent of the FSRP.

15. The sonar system of claim 12, wherein the DSP is further configured to taper either end of the correlation and shaping response.

16. The sonar system of claim 12, wherein the received sonar chirp pulse is an unshaped pulse.

17. A method, comprising:

within a sonar system, dividing a frequency-domain version of the received sonar chirp pulse by a frequency-domain version of the shaped replica pulse (FSRP) to provide a shaping filter response;

multiplying the shaping filter response by a conjugate of the FSRP to provide a combined correlation and shaping response; and

multiplying the frequency-domain version of the received sonar chirp pulse with the correlation and shaping response to produce a correlated and shaped signal.

18. The method of claim 17, further comprising detecting a target within the correlated and shaped signal.

19. The method of claim 17, wherein the received sonar chirp pulse is an unshaped pulse.

20. A method of rejecting sonar interference, comprising:

detecting echoes corresponding to a series of transmitted sonar pulses, each detected echo being represented by a series of time samples;

for each detected echo, comparing a series of time samples to corresponding time samples in a preceding echo and a subsequent echo to determine whether the compared time samples exceed the corresponding time samples by a set limit; and

if the compared time samples exceed the corresponding time samples in the preceding and subsequent echoes by the detection threshold, replacing the compared times samples with alternative sample values.

21. The method of claim 20, wherein replacing the compared time samples comprises replacing each compared time sample with an average of the compared time sample and the corresponding time samples in the adjacent echoes.