Improving downlooking SAS resolution with transmitter spatial diversity

Abstract

Various low frequency down-looking SAS systems have been designed to produce sub-sediment volumetric imagery for the purpose of detecting unexploded ordnance (UXO), cables, pipelines, or other buried objects. These systems create three-dimensional images by combining an across-track physical array with an along-track synthetic aperture to form a down-looking planar array. The low frequencies used to penetrate the sediment necessitate wide physical arrays to achieve useful resolution in the across-track dimension. Space, cost, and mechanical design limitations place a practical upper bound on the physical array length. An alternative method for resolution enhancement is to use transmitter spatial diversity. In the current paper, simulations comparing a dual-transmitter and single-transmitter design are conducted using the design parameters of the Multi-Sensor Towbody (MuST) system developed at APL-UW. The MuST system has a downward looking array composed of multiple EdgeTech Buried Object Scanning Sonar (eBOSS) panels aligned in the across-track dimension. The system has three separate transmitters: one transmitter located near the middle of the array and two transmitters at opposing ends of the array. The MuST system was designed to have two different transmit modes: one in which the active transmitter alternates between opposing ends of the array, and one in which the active transmitter is always near the center of the array. Both point target and bistatic rigid model simulations for these two transmitter configurations indicate that by using the configuration with alternating transmitters the across-track resolution can be increased.