Multispectral and multiangle measurements of acoustic seabed backscatter acquired with a tilted calibrated echosounder.

A multispectral and multiangle analysis of seabed backscatter intensity has been conducted using data from a calibrated single-beam echosounder (SBES) with five frequency channels deployed over four homogeneous areas with different sediment types in the Bay of Brest (France). The SBES transducers were tilted at incidence angles from 0° to 70° to record the seafloor backscatter angular response at discrete frequencies ranging from 35 to 450 kHz. The recorded backscatter levels were analyzed for their angular dependence (average backscatter strength versus frequency and angle) as well as for their sample statistical distribution. The angle and frequency dependence of the seafloor backscatter obtained using a calibrated SBES can potentially be used to calibrate multibeam systems, and it can also help in elucidating the physical processes of backscatter controlled by the interaction between the acoustic wave characteristics and the sediment properties. Backscatter measurements for each area showed a consistent frequency dependence with little variation between the four sediment types.

A statistical approach for analyzing and modeling multibeam echosounder backscatter, including the influence of high-amplitude scatterers.

The statistical analysis of acoustic backscatter samples recorded by multibeam echosounders can be a valuable tool for remote seafloor characterization and interpretation. The present paper aims at analyzing the statistics of backscatter data values, both in "raw" status and after various averaging operations, using field data. It is shown that the statistics of the data can be adequately described by a Weibull distribution parametrized by the incidence angle and the level of applied processing: the distribution of the averaged backscatter amplitude, processed according to various schemes, varies from a Rayleigh law for raw data to lognormal and finally to Gaussian distribution after successive averaging operations. Based on these results, some recommendations for the calculation of the mean backscatter strength are presented. Finally, the influence of high-amplitude scatterers in the backscatter probability density function is addressed; a scheme is suggested to separate the contributions of the substrate from the contributions of the scatterers on the statistical distribution of sonar data samples.