Control of the repeatability of high frequency multibeam echosounder backscatter by using natural reference areas

The increased use of backscattermeasurements in time series for environmental monitoring necessitates the comparability of individual results. With the current lack of pre-calibrated multibeam echosounder systems for absolute backscattermeasurement, a pragmatic solution is the use of natural reference areas for ensuring regular assessment of the backscattermeasurement repeatability. This method mainly relies on the assumption of a sufficiently stable reference area regarding its backscattersignature. The aptitude of a natural area to provide a stable and uniform backscatterresponse must be carefully considered and demonstrated by a sufficiently long time-series of measurements. Furthermore, this approach requires a strict control of the acquisition and processing parameters. If all these conditions are met, stability check and relative calibration of a system are possible by comparison with the averaged backscattervalues for the area. Based on a common multibeam echosounder and sampling campaign completed by available bathymetric and backscattertime series, the suitability as a backscatterreference area of three different candidates was evaluated. Two among them, Carre Renard and Kwinte, prove to be excellent choices, while the third one, Western Solent, lacks sufficient data over time, but remains a valuable candidate. The case studies and the available backscatterdata on these areas prove the applicability of this method. The expansion of the number of commonly used reference areas and the growth of the number of multibeam echosounder controlled thereon could greatly contribute to the further development of quantitative applications based on multibeam echosounder backscattermeasurements.