Methods for Quantifying Mid-Frequency Active Sonar in the SOCAL Range Complex

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A new method was developed to provide better metrics for quantifying Mid-Frequency Active Sonar (MFAS) occurrence and levels, and was applied to passive acoustic monitoring data collected in the Southern California (SOCAL) Range Complex. MFAS signals are composed of both tones and frequency swept ‘pings’, often with multiple pings grouped closely in time as packets. These packets often occur repeatedly at intervals >20 s over periods of hours as wave train events with gaps between events >1 h. The new approach uses a higher received level packet detection threshold (130 dBpp re 1 µPa) than previous analyses, which limits the detection range to about 20 km, reducing the number of overall detections but also reducing the false detection rate.