Detecting surface cracks using acoustic signals

A method for detecting cracks in an underwater structure, the method comprising:

• receiving, from an acoustic field receiver, a first plurality of resulting acoustic fields, wherein the first plurality of resulting acoustic fields emanate from a first plurality of acoustic signals traveling through a first portion of the underwater structure, wherein the acoustic field receiver is disposed proximate to, but without physically contacting, the first portion of the underwater structure;
• receiving, from the acoustic field receiver, a second plurality of resulting acoustic fields, wherein the second plurality of resulting acoustic fields emanate from a second plurality of acoustic signals traveling through the first portion of the underwater structure;
• analyzing the first plurality of resulting acoustic fields and the second plurality of resulting acoustic fields;
• and
• detecting, based on analyzing a third harmonic of the first plurality of resulting acoustic fields and analyzing a third harmonic of the second plurality of resulting acoustic fields, a crack in the first portion of the underwater structure.

A method for detecting cracks in a structure, the method comprising:

• receiving, from an acoustic field receiver, a first plurality of resulting acoustic fields, wherein the first plurality of resulting acoustic fields emanate from a first plurality of acoustic signals traveling through a first portion of the structure, wherein the acoustic field receiver is disposed proximate to, but without physically contacting, the first portion of the structure;
• receiving, from the acoustic field receiver, a second plurality of resulting acoustic fields, wherein the second plurality of resulting acoustic fields emanate from a second plurality of acoustic signals traveling through the first portion of the underwater structure;
• analyzing the first plurality of resulting acoustic fields and the second plurality of resulting acoustic fields;
• and
• detecting, based on analyzing a third harmonic of the first plurality of resulting acoustic fields and a third harmonic of the second plurality of resulting acoustic fields, a crack in the first portion of the structure.