Predictions and Measurements of the Directivity of a Monopole Source in a Floating Ice Plate

Abstract

The directivity of an acoustic monopole in a floating ice plate is examined. Comparison is made between uniform and vertically non-uniform ice and between solutions using the SAFARI numerical propagation code and steepest decent methods. The implications to higher frequency (order 1 kHz) noise resulting from ice fracturing are reviewed. The theory predicts mostly downward radiation, implying that the range to which sound travels is limited by bottom depth. The theory also shows that modeling the ice as a vertically non-uniform plate may be essential. We also see that for shallow grazing angles, events near the ice/air interface radiate better than a source near the center of the ice. An experiment to measure the directivity of a monopole source in ice is described. Comparison of the theory with data is sometimes weak, perhaps indicating that the source configuration did not produce a compact monopole source. However, where comparison was good, greater than expected radiation was measured at low grazing angles, perhaps indicating scattering must be included in the model.