Method, apparatus, and computer program for detecting one or more objects in the sea floor

1 . A method of detecting one or more objects in a sea floor, the method comprising:

transmitting, from one or more acoustic signal sources, a plurality of acoustic signals into the sea floor, wherein a wavelength of the plurality of acoustic signals is selected to be of the same order of magnitude as an expected size of the one or more objects;

obtaining, from a plurality of acoustic receivers, a receiver signal, the receiver signal comprising electrical waveforms generated in response to acoustic pressure waves scattered by the plurality of acoustic signals at the one or more objects in the sea floor;

generating a detection grid, the detection grid representing a grid at the points of which the one or more objects are being localized, the detection grid extending both below an area spanned by the plurality of receivers and offset from the area;

grouping portions of the receiver signal to points of the detection grid;

performing a travel time correction of the portions of the receiver signal with respect to the points of the detection grid to align the electrical waveforms generated by the scattering into a coherent seismic event;

combining the travel time corrected portions of the receiver signal at the points of the detection grid; and

detecting the one or more objects at the points of the detection grid both below the area spanned by the plurality of receivers and offset from the area based on the combination of the travel time corrected portions of the receiver signal, wherein the detection of the one or more objects is based on the scattering of the multiple acoustic signals at the one or more objects.

2 . The method of claim 1 , wherein the one or more objects are detected based on an amplitude of the combination of the travel time corrected portions of the receiver signal.

3 . The method of claim 2 , further comprising calculating an envelope of the amplitude of the combination of the travel time corrected portions of the receiver signal, wherein the one or more objects are detected based on the envelope.

4 . The method of claim 3 , further comprising calculating a coherence function based on the combination of the travel time corrected portions of the receiver signal, wherein the coherence function is based on a similarity between temporally successive portions of the receiver signal, wherein the one or more objects are detected based on the coherence function.

5 . The method of claim 4 , further comprising calculating a weighted envelope based on the envelope and based on the coherence function.

6 . The method of claim 4 , wherein the coherence function is based on a semblance analysis.

7 . The method of claim 1 , further comprising scaling the respective travel time corrected portions of the receiver signal to achieve a signal amplification of signal portions based on the scattering of the multiple acoustic signals at more distant objects of the one or more objects.

8 . The method of claim 1 , further comprising identifying a reflection of the scattering of the acoustic signal at the one or more objects, wherein the reflection of the scattering of the acoustic signal at the one or more objects is disregarded in the detection of the one or more objects.

9 . The method of claim 1 , wherein a constant seismic velocity is assumed for the travel time correction.

10 . The method of claim 1 , wherein the travel time correction is performed for a range of possible seismic velocities, wherein a seismic velocity is selected for the travel time correction from the range of possible seismic velocities based on a magnitude of a local maximum in the corresponding combination of the travel time corrected portions of the receiver signal.

11 . The method of claim 1 , wherein seismic velocities matched to different material layers between the plurality of receivers and the points of the detection grid are used for the travel time correction with respect to the points of the detection grid.

12 . The method of claim 1 , wherein the portions of the receiver signal are grouped to the points of the detection grid based on a distance of the points of the detection grid from the receivers of the plurality of receivers and from at least one signal source of the multiple acoustic signals.

13 . The method of claim 12 , wherein the portions of the receiver signal are grouped to the points of the detection grid separately for each acoustic signal.

14 . The method of claim 12 , wherein the portions of the receiver signal are grouped to the points of the detection grid for a predefined number of time points combined in the predefined time sequence.

15 . The method of claim 12 , wherein the portions of the receiver signal are grouped to the points of the detection grid for a predefined distance of the points of the detection grid from the receivers of the plurality of receivers and from at least one signal source.

16 . The method of claim 1 , wherein the receiver signal comprises a first signal portion based on the scattering of the multiple acoustic signals at the one or more objects, and wherein the receiver signal comprises a second signal portion based on a reflection of the multiple acoustic signals, wherein the method comprises suppressing the second signal portion compared to the first signal portion, wherein grouping the portions of the receiver signal, performing the travel time correction, combining the travel time corrected portions, and/or detecting the one or more objects are based on the first signal portion.

17 . The method of claim 16 , wherein suppressing the second signal portion is based on an eigenvalue decomposition of a travel time corrected version of the receiver signal.

18 . The method of claim 1 , comprising suppressing, in the receiver signal, a reflection of the multiple acoustic signals.

19 . A non-transitory, computer-readable medium having a program code for performing a method of detecting one or more objects in a sea floor when the program code is executed on a computer, a processor, a control module, or a programmable hardware component, the method causing the computer, the processor, the control module, or the programmable hardware component to:

activate an at least one acoustic signal source to transmit a plurality of acoustic signals into the sea floor, wherein a wavelength of the plurality of acoustic signals is selected to be of the same order of magnitude as an expected size of the one or more objects;

obtain, from a plurality of acoustic receivers, a receiver signal comprising electrical waveforms generated in response to acoustic pressure waves scattered by the plurality of acoustic signals at the one or more objects in the sea floor;

generate a detection grid, the detection grid representing a grid at the points of which the one or more objects are being localized, the detection grid extending both below an area spanned by the plurality of acoustic receivers and offset from the area;

group portions of the receiver signal to points of the detection grid;

perform a travel-time correction of the portions of the receiver signal with respect to the points of the detection grid to align the electrical waveforms generated by the scattering into a coherent seismic event;

combine the travel-time-corrected portions of the receiver signal at the points of the detection grid; and

detect the one or more objects at the points of the detection grid both below the area spanned by the plurality of acoustic receivers and offset from the area based on the combination of the travel-time-corrected portions of the receiver signal, wherein the detection of the one or more objects is based on the scattering of the plurality of acoustic signals at the one or more objects.

20 . An apparatus for detecting one or more objects in a sea floor, the apparatus comprising:

an interface coupled to at least one acoustic signal source and a plurality of acoustic receivers, and

a processing module configured to:

activate the at least one acoustic signal source to transmit a plurality of acoustic signals into the sea floor, wherein a wavelength of the plurality of acoustic signals is selected to be of the same order of magnitude as an expected size of the one or more objects;

obtain, from the plurality of acoustic receivers, a receiver signal comprising electrical waveforms generated in response to acoustic pressure waves scattered by the plurality of acoustic signals at the one or more objects in the sea floor;

generate a detection grid, the detection grid representing a grid at the points of which the one or more objects are being localized, the detection grid extending both below an area spanned by the plurality of receivers and offset from the area;

group portions of the receiver signal to points of a detection grid,

perform a travel time correction of the portions of the receiver signal with respect to the points of the detection grid to align the electrical waveforms generated by the scattering into a coherent seismic event,

combine the travel time corrected portions of the receiver signal at the points of the detection grid, and

detect the one or more objects at the points of the detection grid both below the area spanned by the plurality of receivers and offset from the area based on the combination of the travel time corrected portions of the receiver signal, wherein the detection of the one or more objects is based on the scattering of the multiple acoustic signals at the one or more objects.