Near bottom sediment characterization offshore SW San Clemente Island

Normal incidence, 23.5 kHz seafloor acoustic backscatter data and bottom video were measured with the Deep Tow instrument package of the Scripps Institution of Oceanography in 100 meter water depth south of San Clemente Island, CA. The collected data were processed using an echo envelope sediment characterization method, to derive geoacoustic parameters such as particle mean grain size and the strength of the power law characterizing the roughness energy density spectrum of the sediment-water interface. Two regions, sand and silt, were selected based on available ground truth, perceived along-track sediment homogeneity, data quality and tow fish stability. Distinction between sand and fine grain sediments can be accomplished by creation of feature vectors comprised of mean grain size (M_Φ) and interface roughness spectral strength (w₂). Estimates for mean grain size and roughness spectral strength (M_Φ, w₂) were (1.5, 0.0095) for sand, and (6.7, 0.0033) for silt, where M_Φ is expressed in PHI units, and w₂ has units cm⁴. These results are consistent with local ground truth measurements and illustrate the potential of this sediment characterization method in survey mode.