Spherical wave effects in sediment reflection coefficients

Abstract

Several research institutions are investigating models to properly describe high frequency, sandy-sediment, acoustic properties because of their importance in shallow water operations. In this talk we will focus on the error contribution of spherical wave effects on each of four common models: the visco-elastic model, the Effective Density Fluid Model (EDFM), Buckinghams micro-sliding model and the Biot/Stoll poro-elastic model. This will be accomplished by comparing the known models of reflection coefficients to laboratory measurements. Theoretical data will be calculated for each of the models using OASES, which utilizes the depth-dependent Green’s function and a direct global matrix approach to calculate the full field. Parameters for the visco-elastic model have been measured and verified at the test location. Parameters for the EDFM, Buckingham and Biot/Stoll models were determined from measured values and previous inversions of plane wave reflection data taken at the same location. Air/water interface data will be measured and computed for each model as a test case. Linearly Frequency Modulated (LFM) chirps over the range of 30–160 kHz will be used to establish ranges in frequency. [Work supported by ONR, Ocean Acoustics.]