MODELING BISTATIC BOTTOM SCATTERING STRENGTH INCLUDING A FORWARD SCATTER LOBE

Sound scattering from the sea floor is a very complex phenomenon. Although it has been studied extensively, a full understanding of a three-dimensional scattering function is still lacking. Most often cited as the working hypothesis is Lambert's law with an empirical coefficient developed by Mackenzie and a bistatic extension based on assumed symmetry about the vertical. However, this form is deficient in several respects. Two important, but often overlooked, deficiencies are the model's lack of a coherent scattering component and its inability to model a ''forward'' scatter lobe. The Naval Oceanographic and Atmospheric Research Laboratory (NOARL) developed the Bistatic Scattering Strength Model (BISSM) in 1987 to overcome these and other deficiencies. In addition to being able to account for a forward lobe, BISSM includes an ability to compute the local incident, specular, and scattering angles with respect to the local facet normal, and with additional assumptions, it may predict the coherent component. Recent improvements in the capabilities or Navy and civilian survey and academic and international research organizations to resolve bathymetry to fine scales stimulated an upgrade to the original BISSM to make use of these finer scales. Reported here is the upgrade to the BISSM scattering strength algorithm and its integration with broad-coverage high-resolution bathymetric databases. The relationship between BISSM and composite roughness theory is discussed. Also discussed are deficiencies in data support available to BISSM and problems in the algorithm that are fundamental in available scattering theory.