Volume‐Scattering Observations in Puget Sound and Nearby Waters

In March of 1967, observations of volume scattering at 28.5 kHz were made in Puget Sound and nearby waters. Both day and nighttime measurements were taken in eight sequences, spaced over several days, at each of four stations. Pulse width of 1, 3 and 10 msec were transmitted, the shorter pulses having a greater ability for resolving organisms. The observed return consisted of a continuous envelope of reverberation, plus individual echoes from single scatterers. A nighttime upward migration of the scattering layer was observed at most stations. At two stations the average volume scattering coefficient (Sv) attained a value of −46 dB (re: yd2/cubic yd) at a depth of 100–200 ft. The average value of target strength for the 395 individual targets observed was −40 dB, and the extreme values were −85 and −29 dB.