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Measuring Bathymetric Uncertainty of the Edgetech 4600 Sonar

Tom Hiller, Lisa Nicole Brisson

Total propagated uncertainty (TPU) models of sonar systems are required in order to apply sophisticated postprocessing techniques such as the CUBE algorithms.  Empirical measurements of system uncertainty can be used to refine and verify the sonar models and ensure that the TPU used in sonar processing is consistent with the data collected.  In early 2012 a series of tests was carried out to determine the system repeatability of the Edgetech 4600 swath bathymetry and side-scan sonar system.  The 4600 is an interferometric system with eight receive transducers which enhances rejection of multi-path effects, reverberation and acoustic noise.  EdgeTech’s Full Spectrum® chirp processing also provides denser data in the nadir region compared to other interferometric systems.  The aim of the trials was to gather sufficient survey data to measure the 4600 sonar system repeatability, minimising other error sources.  Repeat surveys were run over shallow (3m) and navigation depth (10m) areas in the intercoastal waterway near Lake Worth Inlet, Palm Beach FL, with the aim of generating reference bathymetric surfaces.  Single survey lines were then run over the test areas for comparison with the reference surfaces.  Sonar performance was analysed by comparing the single lines with the reference surface; the single line repeatability plot could then be used as a proxy for the sonar system’s uncertainty.  Statistical techniques were used to determine the system repeatability as a function of horizontal distance from nadir and hence obtain an empirical measure of the sonar’s contribution to the bathymetric uncertainty.