COMBINATION OF BATHYMETRY AND CALIBRATED IMAGERY IN MULTIBEAM ECHOSOUNDER

Abstract: The scientific community and advanced users have a need for accurately calibrated measurements of acoustic properties of the sea bed. The predominant sensors for underwater survey are based on sonar technology. In this category of remote sensing devices, the latest generation of multibeam echosounder provides high-resolution bathymetry and imagery. This combination offers a unique opportunity to improve the accuracy of the final measurement by the inherent co-localization of the two components. In this paper we present an implementation of backscatter computation that includes a calibration procedure and takes advantage of bathymetry knowledge. It demonstrates that, while a variation of imagery intensity can result either from the topology of the seabed or from a change in the sediment composition, the bathymetry provides a means to separate these causes and compensate for topology. Once all the sonar parameters are carefully measured during a calibration routine and accounted for during the backscatter estimation, only the characteristics of the sediment are present in the resulting data set. This calibration procedure is a critical step of the process as any error during that operation will translate in a loss of accuracy in the final results. The work presented in this paper targets a high-resolution high-frequency system. After the necessary information about this system has been collected during calibration, calibrated backscatter is computed in post-processing on raw data collected during the survey. A test is performed to verify the validity of the implementation and a sample survey is conducted for final validation