Meet Marc Pinto, ECA Group's Robot system program Director to talk about different naval-centered themes.
Thursday 25th October at 9.10 am for the first ECA Group conference, in Ballroom C1.
The long term accuracy (i.e. bias) of Synthetic Aperture Sonar micronavigation using a Displaced Phase-Center Antenna (DPCA) is studied theoretically. We consider a linear
array in an isovelocity medium, in uniform translation with relative trim over a locally planar and homogeneous seabed. For a given range, assuming a narrow field of view, it is shown that the trim introduces a bias on the cross-range displacement in the seabed plane, due to a frequency-independent projection error.
It is also shown that the bias on the line of sight displacement depends on the two components of displacement in plane of sight (defined as the plane normal to the seabed containing the line of sight), the grazing angle, the trim and the square of the rms transmit-receive beamwidth of the DPCA element. This last bias is shown to result from a Fresnel diffraction effect due to a depth of field problem. The impact of these biases on SAS image quality is assessed. It is shown that image degradation results solely from the line-of-sight bias but that the effect is generally very small.
Finally, it is shown that, using an Interferometric Synthetic Aperture Sonar, both the grazing angle and the relative trim angle can be estimated, and all DCPA displacements referred to a vehicle-fixed frame. By combining port and starboard DPCA estimates, the Cartesian velocity vector can be reconstructed, ready for integration in an aided inertial navigation system.
Later the same day, another conference will be held at 3:40 pm. in ballroom C1
The long term accuracy (i.e. scale factor) of a Doppler Velocity Sonar for speed over seabed estimation is studied theoretically, using a simplified physical model. A classical 150 kHz piston DVL, which averages the Doppler phase over the entire beam footprint, is compared with the same piston operated in a new range-gated mode, to reduce the spread in echo strength which biases the estimation. The predicted absorption and terrain biases are lower than 0.1% for the range-gated DVL, whereas they vary between 0.3% and 1% for the classical DVL, depending on operating altitude and grazing angle.
To exploit this benefit of range-gating, the direction of arrival of the echoes from the gate must be accurately estimated in the piston frame, e.g. the gate must be centered on the piston axis without bias. It is shown how this can be achieved by an improved Interferometric DVL design which splits the piston into at least two phase centers, and centers the gate using the zero-crossing of the differential Doppler phase. A 0.1% accuracy at more than 500m altitude above the seabed should therefore be achievable with the new InDVL instrument.
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