Working together in Seattle, we are still struggling to understand and compute how loud commercial ships are at high-frequencies (1-100 kHz). In pursuit of the optimal way to convert our receive levels into source levels, we are considering spherical spreading vs a frequency-dependent model informed in part by our tonal transmission loss experiments at Lime Kiln. We also MUST tackle how to apply the physics of sound absorption in sea water, at least for those ships for which we have measured a signal above noise in the 10-100 kHz frequency range.
Today Val is working on comparing 1/3 octave band levels for a few key ships with measurements made by JASCO. He is also comparing our transmission loss experimental results with theirs, ideally seeing whether we have similar frequency-dependent spreading models and assessing how different they are from a simple assumption of spherical spreading with or without absorption.
I continue scouring the literature (some of it rooted in WWII Naval measurements) for comparable measurements of surface ship noise. I’m also trying to understand cavitation better, including searching for any measurements of noise from cavitating propellers and/or ships. Thus far the best recent examples are Kipple and Hildebrand’s single ship (among many measurements of noise below ~1 kHz), but I’ve just found some declassified measurements of surface ships and submarines that appear to extend up into the 10-100 kHz range.
On a procedural note, I need to add Zotpress to this blog so I can insert citations properly…