Accuracy assessment of depth estimates from variation in pre- and post-processing of multi-beam SONAR surveys in a fjord environment
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[author abstract] The demand for accurate, high resolution bathymetric maps has risen with increases in utilization of offshore resources. This demand has been met with advances in technology. However, surveyors must trade-off between high data quality and minimizing survey costs. Outer beams of modern multi-beam SONAR systems, particularly when wide-beam swaths are used, return the most errors, as opposed to the nadir of a survey track-line. This is due, in part, to the inherently wider beams and the greater amount of time required for the outer angled pings to reach their destination and return. This study closely examined the accuracy of the Kongsberg EM302 outer beams during a survey in a fjord environment aboard the R/V Thomas G. Thompson. An area within Nootka Sound, British Columbia, Canada was surveyed first with a control and then the outer beams of both wide-beam and narrow-beam swaths were aligned with the center line (nadir) of the control survey. ...The results of this investigation illustrate that the outer beams of a wide-beam survey produce a significant number of errors compared to the nadir beams and that sound velocity is a contributing factor to post-processing error.