Low frequency active sonar (LFA) bottom loss requirements

Abstract

A bottom interaction simulator was developed to investigate LFA bottom bounce losses, i.e., the mismatch losses, which occur in matched filter processing of bottom and target reflected signals due to the time spreading (dispersion) of the signal caused by these boundaries. The motivation behind this was the need to address bottom loss data base deticiencies to aid in future upgrades which would support LFA sonar. The simulator provided a "tool" to examine the mismatch issue and determine the mismatch losses in a low costilow risk approach to bound the problem. The mismatch loss, the additional loss over that of a non-spread signal, is given for a number of realistic situations where measured impulse response functions represent the spreads in a series of convolutions. The target was a 100: 1 scale model of a simple cylindrical shape with rounded endcaps. The bottom was reprcsl!nted by previously obtained SACLANT Undersea Research Center impulse response data . The results indicate that only under ideal (no spread) conditions will a total energy bottom loss data base support LF A sonar performance predictions where coherent processing is used. This highlights the need for the bottom loss data base to include the effects of these spreads.