Measurement of sea bed topography and bistatic scattering coefficients with steered frequency source arrays

A method of measuring bottom topography and bistatic scattering coefficients with steered frequency source (SFS) arrays is described and illustrated with modeled reverberation data. SFS array design principles are summarized and methods of analyzing the data to obtain sea bed topography and bistatic scattering coefficients are outlined. The SFS source radiates acoustic energy in a set of narrow vertical beams, each at a different frequency. The source consists of a vertical line array of impulsive charges which are detonated in a time delayed sequential order. This generates a set of nested expanding wave fronts centered at each source element. The observed frequency in each vertical beam is defined by the spacing between the wave fronts measured along a vertical angle of departure from the center of the source. Sea bed topography can be measured with the deployment of a distributed field of azimuthally directive receivers and multistatic SFS source arrays. High resolution topography is calculated from the time/frequency return structure of the bottom scattered reverberation by resolving the bistatic intersection of the SFS vertical source beams and the azimuthal directive receivers. The magnitude of the reverberation, at any given bistatic intersection, is a measure of the bistatic scattering function of the reverberating surface. The strength of the reverberation is related to the bistatic scattering coefficient via the RUMBLE reverberation model of Bucker et al. (1993)