Originally Posted by DJ77
Can we assume that a 20db signal to noise ratio is about the detection capability of TPLs ?
If they were using a traditional detector, which consists of a narrow-band filter, a peak detector and a threshold comparison, then 20db would be about right. If they are doing more modern signal processing, then it might be considerably better (another 10-15db, perhaps).
Since we are in the ITCZ intermittent heavy showers have a significant probability of occurring at any time. I read in a US Navy paper that rain drops impacting sea surface and implosion of air bubbles caused by rain produce noise in the 1-100 kHz band with max SL @ 20 kHz and SL can be up to 30 dB above sea surface noise though I think the intensity is lower at great depths.
Those numbers sound about right. I expect that the 30db increase is compared with sea state 0; the increase will be comparatively less if the surface already has breaking waves. Also, these high frequencies are attenuated with distance, as I noted in the earlier post; so, yes, the effect will be less at depth. Also, at 4000m depth, the rain noise is being averaged from a similar radius area of the sea surface; thus a rain shower that does not cover that whole area of the sea surface, will have a lower total effect.