default Calibration of cardioid beamforming algorithms

By

Calibration of cardioid beamforming algorithms. NURC-FR-2006-003. May 2006.

Many nations are now using or considering cardioid towed arrays as their principle receive array in active low frequency sonar applications.A drawback of cardioid array beamforming is that it is not obvious how the obtained signal levels, after processing, relate to the hydrophone pressure level. Calibrated signal levels are important, for example, for the comparison of processed cardioid data with sonar model predictions or to measure the difference in performance between cardioid arrays and line arrays. In this report mathematical expressions are derived that allow, in the case of CW or LFM signals, calibration of the cardioid processed data. The validity of these expressions is demonstrated with simulated and real active sonar data.