CHARACTERIZATION OF SURFACE ROUGHNESS ALONG THE ROCKY COASTLINE USING STEREO PHOTOGRAPHY TECHNIQUES

Abstract

High-resolution images have been used to estimate and characterize the roughness of the rocky seafloor in terms of small-scale roughness and power spectral density. The application of this work is acoustical modeling of scattering from the sea floor. Two camera systems were designed and built to collect images of the ten different types of surfaces along the rocky shoreline on the Monterey Peninsula at low tide. Using commercial photogrammetry software, the images were processed to calculate height Digital Elevation Maps, which were then used to estimate 1-D and 2-D roughness power spectra. A power-law model was fit to the spectrum and had two parameters, the spectral strength and spectral slope. These roughness power spectra parameters were compared to previously collected parameter data on sandy seafloor, and the scattering strength values were compared to recently collected data along the same rocky coastline of the Monterey Bay. The lower-frequency rocky seafloor spectral strength and slope showed overlap with some of the sand surfaces at varying spatial scales. These parameters were used as inputs into a small-scale roughness perturbation theory model to predict scattering strength of the ten different surfaces for a frequency of 200 kHz and three different grazing angles. The predictions using this scattering strength method were within 10 dB of measurements collected within the same area in the Monterey Bay.