Nistad/Westfeld: Fusion of Measured and Synthetic Sound Speed Profiles .
this work took place. In early 2021, a new implementation of the BSH regional
forecast model was released (now called BSH-HBM), which enhances BSHcmod
by increasing the depth resolution and improving the quality of the forecast data.
This updated model warrants a new evaluation. Finally, another advantage of
models such as BSH-HBM in hydrographic operation is their utilization as plan-
ning tools prior to survey operations.
In order to evaluate the accuracy of interpolation in compensating for the lack
of measured sound speed profiles, the MVP-30 dataset was sequentially subsam-
pled; removed measured profiles were replaced with interpolated profiles and
the impact of this change displayed as histograms (Fig. 2 left) and quantified
as an RMS deviation of vertical biases. Interpolation displays a maximum RMS
gain of 0.04 % of depth, representing 1 cm in 20 m depth. While this value may
seem small, it represents the average for an entire dataset. The impact is much
more pronounced when viewed for a single survey line within a dataset in which
sound speed errors are known to be present. Fig. 2 (right) illustrates the gain in
terms of reduced systematic and random error as a function of beam angle for a
single survey line. For the higher beam angles, a factor three reduction in vertical
bias is shown to be possible.
In order to guarantee the absence of sound speed induced beam steering er-
rors, an evaluation of the MVP-30 dataset was attempted. During this process, it
was discovered that a bias above 0.25 % of depth (5 cm in 20 m depth) for higher
beam angles might be present. It is therefore hypothesized that a beam steering
error is present in the datasets. Given that the surface sound speed sensor is
subjected to a regular maintenance and calibration schedule, it is unlikely that a
factory calibration would resolve the issue. A new project has been initiated to
determine the exact cause of this problem.
References
Nistad, J.-G., Westfeld, P. (2022): Improved Techniques to Resolve the Water Column
Sound Speed Structure for Multibeam Ray-Tracing. In: International Hydrographic
Review.
Roemer, S., Hodnesdal, D. A., Ofstad, A. E., Dias, A.E (2017): Sound velocity profile in-
terpolation in space and time - a way to overcome one of the nightmares of mul-
ti-beam processing? Paper presented at the Teledyne CARIS International User Group
Conference, 2017/19-22 June.
Contact
Jean-Guy Nistad | Dr.-Ing. Patrick Westfeld
Federal Maritime and Hydrographic Agency
Neptunallee 5, D-18057 Rostock
jean-guy.nistad@bsh.de | patrick.westfeld@bsh.de
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