Abstract

A method of filtering an acoustic B-scan (500) for passive detection of an object (106, 108) underwater comprising ensonifying (400) a region (104) of an underwater environment (102) and receiving (402) acoustic signals from the ensonified region (104) of the underwater environment (102), the received acoustic signals corresponding to a plurality of sonar beams. The method also comprises generating (404) the acoustic B-scan (500) from the received acoustic signals and pre-processing (406-414) the acoustic B-scan (500) to remove historic artefacts and mitigate influence of reverberant energy. Energy content is then scored (416) in respect of the pre-processed acoustic B-scan (524) to provide a plurality of energy scores and at least one local maximum (200) of the plurality of energy scores is; identified (418). A predetermined criterion is then applied (808) to a local maximum (700) of the at least one local maximum (700) identified.

IPC Classes  ?

• G01S 7/531 - Scan converters
• G01S 7/527 - Extracting wanted echo signals
• G01S 7/539 - Details of systems according to groups , , of systems according to group using analysis of echo signal for target characterisationTarget signatureTarget cross-section
• G01S 15/66 - Sonar tracking systems
• G01S 15/89 - Sonar systems specially adapted for specific applications for mapping or imaging

Abstract

A method of pre-processing acoustic signals received from an ensonified region (104) of an underwater environment (102) for passive detection of an object (106, 108) in the underwater environment (102). The method comprises generating (404) an acoustic B-scan (500) in respect of a predetermined time frame, and selecting (406) a temporal portion (502) of the acoustic B-scan (500) in accordance with a predetermined selection criterion. The method also comprises compressing (408) the selected temporal portion (502) of the acoustic B-scan (500) to provide a compressed acoustic B-scan (510), and applying (410) a B-scan background mask (512) to the compressed acoustic B-scan (510) to suppress any historic reflectivity samples of the compressed acoustic B-scan (510) and to provide an extant compressed acoustic B-scan (524), A dynamic range of the extant compressed acoustic B-scan (524, 600, 602, 604) is then suppressed (412).

IPC Classes  ?

• G01S 15/66 - Sonar tracking systems
• G01S 7/527 - Extracting wanted echo signals
• G01S 7/53 - Means for transforming co-ordinates or for evaluating data, e.g. using computers
• G01S 15/87 - Combinations of sonar systems

Abstract

A method of measuring underwater depth comprising: an active sonar translating (420) in a predetermined direction of travel through a water column, the active sonar having an acoustic transducer. A region of the water column is ensonified (402) as the active sonar travels over a plurality of time frames. A plurality of reflections is received (404) in respect of each of the plurality of time frames and each of a plurality of selected locations to be measured within a field of view of the transducer. A plurality of slant ranges and corresponding slant angles to the selected locations for each of the plurality of time frames is calculated. The slant ranges and slant angles and an estimate of a degree of refraction in the water column are used to calculate (416) a plurality of normalised depth estimates. A global relationship between the plurality of normalised depth estimates and squares of the plurality of slant ranges is modelled (584), and the relationship is used to update (588) the degree of refraction in respect of the plurality of selected locations.

IPC Classes  ?

• G01S 7/52 - Details of systems according to groups , , of systems according to group
• G01S 7/53 - Means for transforming co-ordinates or for evaluating data, e.g. using computers
• G01S 15/89 - Sonar systems specially adapted for specific applications for mapping or imaging

Abstract

A method of filtering an acoustic B-scan (500) for passive detection of an object (106, 108) underwater comprising ensonifying (400) a region (104) of an underwater environment (102) and receiving (402) acoustic signals from the ensonified region (104) of the underwater environment (102), the received acoustic signals corresponding to a plurality of sonar beams. The method also comprises generating (404) the acoustic B-scan (500) from the received acoustic signals and pre-processing (406 - 414) the acoustic B-scan (500) to remove historic artefacts and mitigate influence of reverberant energy. Energy content is then scored (416) in respect of the pre-processed acoustic B-scan (524) to provide a plurality of energy scores and at least one local maximum (700) of the plurality of energy scores is; identified (418). A predetermined criterion is then applied (808) to a local maximum (700) of the at least one local maximum (700) identified.

IPC Classes  ?

• G01S 7/539 - Details of systems according to groups , , of systems according to group using analysis of echo signal for target characterisationTarget signatureTarget cross-section
• G01S 15/42 - Simultaneous measurement of distance and other coordinates
• G01S 15/46 - Indirect determination of position data
• G01S 15/87 - Combinations of sonar systems
• G01S 15/89 - Sonar systems specially adapted for specific applications for mapping or imaging

Abstract

A method of pre-processing acoustic signals received from an ensonified region (104) of an underwater environment (102) for passive detection of an object (106, 108) in the underwater environment (102). The method comprises generating (404) an acoustic B-scan (500) in respect of a predetermined time frame, and selecting (406) a temporal portion (502) of the acoustic B-scan (500) in accordance with a predetermined selection criterion. The method also comprises compressing (408) the selected temporal portion (502) of the acoustic B-scan (500) to provide a compressed acoustic B-scan (510), and applying (410) a B-scan background mask (512) to the compressed acoustic B-scan (510) to suppress any historic reflectivity samples of the compressed acoustic B-scan (510) and to provide an extant compressed acoustic B-scan (524). A dynamic range of the extant compressed acoustic B-scan (524, 600, 602, 604) is then supressed (412).

IPC Classes  ?

• G01S 7/539 - Details of systems according to groups , , of systems according to group using analysis of echo signal for target characterisationTarget signatureTarget cross-section
• G01S 15/46 - Indirect determination of position data
• G01S 15/87 - Combinations of sonar systems
• G01S 15/89 - Sonar systems specially adapted for specific applications for mapping or imaging