Automatic compensation for seafloor slope and depth in post-processing recovery of seismic amplitudes

摘要

Acoustic remote sensing remains the main tool for seafloor exploration across large areas. Acoustic-reflection analysis and acoustic-backscatter analysis allow for the remote estimation of several seafloor and underground properties, which can be further verified by other data such as seafloor cores and samples. Acoustic waves, however, respond not to just geological factors, like bulk density and sediment grain size, but also to the acquisition geometry, including bathymetry. Bathymetry is usually measured by single-beam and multibeam echo sounders, while high-frequency seismic data is acquired with sub-bottom profilers, boomers etc. In order to estimate geological parameters from high-frequency seismic data, it is important to compensate the seismic amplitude for depth and seafloor slope. The seismic acquisition gain can be automatically compensated in real time during the survey, or during post-processing. The former is more adequately used as a first approximation, while the latter offers results that are more precise. An automatic post-processing algorithm is here presented, which detects the sea-bottom for each time series recorded for each seismic trace. Once the bottom is detected, the algorithm calculates the average energy around the detection point, and applies gain compensation to this signal based on bathymetric and seafloor slope information, both obtained from the multibeam sonar data. In order to calculate the amount of gain compensation, least-squares estimation is employed to the average energy of the signal as a function of two-way travel time and wave incidence angle. The algorithm is then tested on real data captured at the Almirantado Bay in King George Island, Antarctica, showing promising results.