System and method of tracking an object that is at least partly buried in seabed
The disclosure relates to a system for tracking an object that is at least partly buried in seabed, the system comprising: An Autonomous Underwater Vehicle (AUV) having a hull, a controlled electric dipole source mounted on the hull of the AUV; first sensor assembly mounted on the hull in the proximity of starboard side of the AUV ( 1 ); second sensor assembly mounted on the hull in the proximity of port side of the AUV; wherein the first and the second sensor assemblies are configured to measure magnetic field from electromagnetic energy transmitted from the controlled electric dipole source. The disclosure further relates to a method of tracking an object that is at least partly buried in seabed.
1 . A system for tracking an object that is at least partly buried in seabed, the system comprising:
an Autonomous Underwater Vehicle, AUV, comprising:
a hull,
a first sensor assembly mounted on the hull in proximity to a starboard side of the AUV;
a second sensor assembly mounted on the hull in proximity to a port side of the AUV; and
a controlled active electric dipole source for transmitting electric current in sequences mounted on the hull of the AUV,
wherein the first sensor assembly and the second sensor assembly are configured to measure a magnetic field from electromagnetic energy transmitted from the controlled active electric dipole source,
wherein the first sensor assembly and the second sensor assembly are separated from one another by a distance d in a direction that is perpendicular to a longitudinal direction of the AUV, and
wherein the system further comprises:
a processor configured to use measurements from the first sensor assembly and the second sensor assembly to estimate a position of a part of a buried object underneath or close to the AUV by inversion of magnetic field data using amplitudes and phases of the magnetic field measured by the first sensor assembly and the second sensor assembly.
2 . The system according to claim 1 , further comprising a tracking algorithm for calculating uncertainties of an estimated position of the part of the buried object based on input of the estimated position.
3 . The system according to claim 2 , wherein the tracking algorithm comprises a Kalman filter.
4 . The system according to claim 1 , wherein further comprising inversion algorithms that is a least-square minimization algorithm in which a function of a difference between modeled magnetic field data and measured magnetic field data is minimized with respect to coordinates of the part of the buried object underneath or close to the AUV.
5 . The system according to claim 1 , wherein the controlled active electric dipole source comprises at least two metal electrode plates mounted on an outside of the hull of the AUV.
6 . The system according to claim 1 , wherein the first sensor assembly and the second sensor assembly each comprises 3-axes magnetometer.
7 . The system according to claim 1 , further comprising one or more 3-axes gradiometers.
8 . The system according to claim 1 , wherein the controlled active electric dipole source operates in a frequency range between 10 and 10000 Hz, or between 100 and 1000 Hz.
9 . The system according to claim 1 , further comprising one or more acoustic sources for transmitting acoustic signals and acoustic sensors for recording a reflected acoustic signal from the buried object.
10 . The system according to claim 1 , wherein the processor is further configured to estimate a position of the buried object relative to the AUV is estimated from the magnetic field data obtained using the first sensor assembly and the second sensor assembly.
11 . A method of tracking an object that is at least partly buried in seabed, the method comprising:
deploying the AUV according to claim 1 ;
transmitting the electric current in sequences from the AUV, having the hull equipped with the controlled active electric dipole source;
measuring magnetic field amplitude and phase with the first sensor assembly and the second sensor assembly mounted on the AUV, wherein the first sensor assembly and the second sensor assembly are separated from one another by the distance d in the direction that is perpendicular to the longitudinal direction of the AUV; and
estimating the position of the part of the buried object underneath or close to the AUV by the inversion of the magnetic field data using the amplitudes and the phases of the magnetic field measured by the first sensor assembly and the second sensor assembly.
12 . The method according to claim 11 , further comprising calculating uncertainties of an estimated position of the part the buried object by a tracking algorithm based on the estimated position.
13 . The method according to claim 12 , further comprising using a Kalman filter for the tracking algorithm.
14 . The method according to claim 11 , wherein the inversion of the magnetic field data comprises using a least-square minimization algorithm and minimizing a function of differences between modeled magnetic field data and measured data with respect to coordinates of the part of the buried object underneath or close to the AUV.
15 . The method according to claim 11 , wherein the electromagnetic energy transmitted by the controlled active electric dipole source has a 1-10 seconds output sequence and
contains discrete frequencies between 10 and 10000 Hz, or between 100 and 1000 Hz.
16 . The method according to claim 11 , wherein the buried object is a pipeline.
17 . The method according to claim 11 , wherein the processor is further configured to steer the AUV along the buried object.