Wideband sonar receiver and sonar signal processing algorithms

• US 9,470,779 B2
• Filed: 04/24/2014
• Issued: 10/18/2016
• 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
• Primary Examiner(s): PIHULIC, DANIEL T
• Application Number:
  US14/261,316
• Publication Number:
  US 20140286131A1
• Time in Patent Office: 908 Days
• US Class Current: 1/1
• 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 shaped baseband replica samples, wherein the correlator comprises a digital signal processor (DSP) configured to divide a frequency-domain version of the shaped baseband replica samples (FSRS) by a frequency-domain version of the baseband samples (FS) to provide a shaping filter response, to multiply the shaping filter response by a conjugate of the FSRS to provide a combined correlation and shaping response, and to multiply the FS with the correlation and shaping response to produce a correlated and shaped 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, and wherein the shaped baseband replica samples correspond to a replica signal shape different from that of the received sonar signal.

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 and shaped signal and extract a power of complex correlation results of the correlated and shaped 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 1, wherein the analog-to-digital converter converts according to a subharmonic sampling rate.

6. The wideband sonar receiver of claim 1, wherein the analog-to-digital converter converts according to a rate of four times a center frequency for the received sonar signal.

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

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

filtering the received wideband sonar signal using the selectable bandpass filter according to the selected filter band;

digitizing the filtered wideband sonar signal to produce digitized samples; and

correlating the digitized samples with shaped replica samples, wherein the correlating comprises dividing a frequency-domain version of the shaped replica samples (FSRS) by a frequency-domain version of the digitized samples (FS) to provide a shaping filter response, multiplying the shaping filter response by a conjugate of the FSRS to provide a combined correlation and shaping response, and multiplying the FS with the correlation and shaping response to produce a correlated and shaped signal.

8. The method of claim 7, further comprising applying a time-varying gain to the filtered wideband sonar signal.

9. The method of claim 7, wherein the digitizing occurs according to a subharmonic sampling rate.

10. The method of claim 7, 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 a basebanded version of the digitized samples before correlating the basebanded version of the digitized samples with a basebanded version of the shaped replica samples.

20. A method of rejecting sonar interference in the received wideband sonar signal processed according to the method of claim 7, comprising:

detecting echoes corresponding to a series of transmitted sonar pulses, wherein each detected echo is represented by a series of time samples, and wherein one of the detected echoes corresponds to the received sonar signal;

for each detected echo, comparing a series of comparison time samples in the one detected echo to corresponding time samples in a preceding echo and a subsequent echo to determine whether detection levels in the comparison time samples exceed the set threshold and exceed the corresponding time samples by a set margin; and

if the comparison time samples exceed the set threshold and the set margin, replacing the comparison samples with alternative sample values determined from the comparison time samples and/or the corresponding time samples in the adjacent echoes.

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

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 shaped replica pulse (FSRP) by a frequency-domain version of the received sonar chirp pulse (FS) to provide a shaping filter response, to multiply the shaping filter response by a conjugate of the FSRP to provide a combined correlation and shaping response, and to multiply the FS 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 further 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, and/or wherein the shaped replica pulse comprises a replica pulse shape different from that of the received sonar chirp pulse.

16. The sonar system of claim 12, wherein the received sonar chirp pulse is an unshaped pulse and/or a symmetric chirp pulse.

17. A method, comprising:

within a sonar system, dividing a frequency-domain version of a shaped replica pulse (FSRP) by a frequency-domain version of a received sonar chirp pulse (FS) 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 FS 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 and/or a symmetric chirp pulse.