Analysis of multibeam-Hydrosweep echo peaks for seabed characterisation

Echo-peak data of outer and normal incidence beams from five different Southern Ocean bottom topographic regions have been analysed. The Rice and Extremal probability density function (PDF) statistical approaches reveal that the seabed roughness is, in general, Gaussian in nature except in the case of the Kainan Maru seamount summit (area D). The outer beams of the Enderby abyssal plain (area C) echo-peak PDF statistics reveal the highest possible large-scale feature dominance. Interestingly, Extremal PDF fit parameters ( alpha ) from the Agulhas Basin (area A) show a less dominant large-scale roughness than in the case of area C. Large-scale feature dominance up to 15 degree beam angle is observed in the case of mixed roughness seabeds such as area B (southwest Indian ridge) and area E (Meteor Rise). No increase in the 30 degree -beam Extremal PDF parameters is observed in these areas. Maximum microtopographic roughness is documented in area D on the summit of Kainan Maru seamount. The estimated fit parameters using Extremal statistics of outer-beam peak data provide a better understanding of the scattering process. Previously determined power law and volume roughness parameters using composite roughness theory are given for the five different areas. These support the results obtained using Rice and Extremal PDFs. The existence of higher volume roughness parameters and power law parameters for medium-scale roughness, along with dominant microtopographic features, are evident from the results of this study.