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Accuracy of Synthetic Aperture Sonar Micronavigation Using a Displaced Phase Centre Antenna: Theory and Experimental Validation

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Technical rept.

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The Cramer-Rao Lower Bounds CRLBs on the cross-track translation and rotation of a Displaced Phase Centre Antenna DPCA in the slant range plane between two successive pings known as DPCA sway and yaw in what follows are computed, assuming statistically homogeneous backscatter. These bounds are validated using experimental data from a 118-182 kHz sonar, showing an accuracy of the order of 20 microns on the ping-to-ping cross-track displacements. Next, the accuracy required on the DPCA sway and yaw to achieve a given Synthetic Aperture Sonar SAS beam pattern specification, specified by the expected SAS array gain, is computed as a function of the number P of pings in the SAS. Higher accuracy is required when P increases to counter the accumulation of errors during the integration of the elementary ping-to-ping estimates the standard deviation must decrease as P super -12 for the DPCA sway and P super -32 for the yaw. Finally, by combining the above results, the lower bounds on DPCA micronavigation accuracy are established. These bounds set an upper limit to the SAS length achievable in practice. The maximum gain Q in cross-range resolution achievable by a DPCA micronavigated SAS is computed as a function of the key SAS parameters. It is found that, for P greater than 1, the optimum SAS spatial sampling factor is 4, in the sense that it allows maximum Q. These theoretical predictions are compared with simulations and experimental results. 8 figures, 13 refs.

Subject Categories:

  • Acoustic Detection and Detectors
  • Underwater and Marine Navigation and Guidance
  • Target Direction, Range and Position Finding

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