SONAR METHOD AND APPARATUS

• US 20160084947A1
• Filed: 04/10/2014
• Published: 03/24/2016
• Est. Priority Date: 04/16/2013
• Status: Abandoned Application

• Current Assignee: Kongsberg GeoAcoustics Ltd.
• Original Assignee: Kongsberg GeoAcoustics Ltd.
• Inventors: HOGARTH, Peter Ian, TAMSETT, Duncan
• Application Number:
  US14/785,041
• Publication Number:
  US 20160084947A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01S 15/8902 Side-looking sonar
• CPC Class Codes: G01S 7/52004 Means for monitoring or calibrating short-range imaging G01S7/5205
• CPC Class Codes: G01S 7/523 Details of pulse systems short-range imaging G01S7/52017; methods or devices for transmitting, conducting or directing sound G10K11/18
• CPC Class Codes: G01S 7/539 using analysis of echo signal for target characterisation; Target signature; Target cross-section

Abstract

A method of calibrating a side scan sonar system by allowing the sonar transducer to roll with respect to the plane of a reference surface to be scanned; measuring the roll angle of the transducer during collection of backscattered sonar data; using backscattered sonar data from a range of transducer roll angles and the measured roll angle to decouple the operating characteristics of the transducer from the angular backscatter characteristics of the reference surface; thereby obtaining an estimate of the operating characteristics of the transducer.

Claims

1. A method of calibrating a side scan sonar system, said system comprising a sonar transducer, said method comprising the steps of:

allowing the sonar transducer to roll with respect to the plane of a reference surface to be scanned;

measuring the roll angle of the transducer during collection of backscattered sonar data from the surface to be scanned;

using backscattered sonar data from a range of transducer roll angles and the measured roll angle to decouple the operating characteristics of the transducer from the angular backscatter characteristics of the reference surface;

thereby obtaining an estimate of the operating characteristics of the transducer.

2. A method according to claim 1 comprising the steps of calculating a plurality of beam sub-functions corresponding to the relative angular transducer response over an angular range encompassed by the range of measured roll angles, said sub-functions together comprising an overlapping set of functions spanning the angular operating field of the transducer;

normalizing the sub-functions with respect to each other by minimization of the overlapping regions;

combining said normalized sub-functions to form a single composite beam function for the transducer.

3. A method according to claim 2 comprising the steps of:

using the composite beam function to estimate the backscatter characteristics of the reference surface by use of the collected backscatter data and the measured roll angle;

using said estimated backscatter characteristics to determine an improved beam function from collected backscatter data and the measured roll angle.

4. A method according to claim 1 wherein said side scan sonar system comprises a plurality of transducers, and the method further comprises the steps of:

using the estimated beam function for each transducer to determine a common estimate of backscatter characteristics of the reference surface; and

using said common estimate of backscatter characteristics to determine a further improved beam function for each transducer.

5. A method according to claim 1 comprising the steps of:

calculating a plurality of seabed scatter sub-functions, each corresponding to the intensity of seabed backscatter over an angular range encompassed by the range of measured roll angles, said sub-functions together comprising an overlapping set of functions spanning the angular range of inclination angles represented in the data;

normalizing the seabed scatter sub-functions with respect to each other by minimization of differences between overlapping regions;

combining said normalized seabed scatter sub-functions to form a single composite scatter function;

using said composite scatter function to derive a beam function from the backscattered sonar data.

6. A method according to claim 5 wherein said side scan sonar system comprises a plurality of transducers, and the method further comprises the steps of:

using the composite scatter function from each of said transducers to determine a single seabed scatter function; and

using this single seabed scatter function to derive a beam function for each transducer from the backscattered sonar data.

7. A method according to claim 1 wherein bathymetry data is further used to correct for the slope of the reference surface.

8. A side scan sonar system configured to incorporate a calibration method according to claim 1.

9. A data processing system, for processing side scan sonar data, configured to incorporate a calibration method according to claim 1.

10. A method of calibrating a side scan sonar system substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings.

11-12. -12. (canceled)