Using data from immobile benchmarks to work out significance of differences between multibeam swaths

What is it about?

Multiple beam echo-sounders work by measuring the range to the seabed in a series of narrow beams oriented in a fan across the track followed by a vessel. When trying to detect changes in the seabed (in our case, associated with the migration of sand dunes), there are a number of sources of uncertainty with different characteristics. For example, errors in estimating tidal height change or effect of burning fuel on the echo-sounder transducer depth are slowly varying and can be treated as simple biases when studying short (in time) lengths of data. On the other hand, motion sensor uncertainties affect the data with shorter periods and different beams differently, with roll errors in particular affecting the outer beams. Studying how depth differences vary after filtering the data over different spatial scales and for different beams can help to quantify some of these uncertainties. Ultimately, the intention is to derive estimates of uncertainty in depth change that can be used to mask out areas of insignificant differences between survey datasets.

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