Effects of Surface Reflection on Bearing Tracker Performance

Recent at-sea testing of a passive sonar bearing tracker indicated that received signal propagation paths which include a surface reflection can result in a substantial increase in bearing error variance. Measurements at high signal-to-noise ratio showed excessive bearing error variance compared to both theory and other measurements when measured Depression/Elevation angle indicated a surface reflected path. It is hypothesized that wavefront scattering due to surface waves is the mechanism for this increase. Based on a Pierson-Moskowitz surface wave spectrum, a simplified acoustic propagation model, the actual test geometry and the parameters of the broadband tracker, effects of surface reflection on tracker performance were analyzed. Resulting work yielded a simple equation which relates random error to surface reflection dependent on (1) test geometry, (2) wind velocity and direction, (3) spatial correlation coefficients between specular points, and (4) the phase center separation between half- beams. Results of calculations show good agreement with the experimental data.