Hydrophone calibration in a tank vs open water?

Question

I’m looking to calibrate some hydrophones (specifically SoundTrap 300HFs, but perhaps this applies more broadly). I’m aiming to compare the SoundTrap hydrophone with a reference one, roughly following Chloe’s previous post on SoundTrap calibration at high frequencies using short pulses (SoundTrap calibration at high frequencies).

We have access to a glider balance tank (MRF), roughly 3m x 1.5m and 1m deep, or to a bay which contains a small marina, and so is unlikely to be particulalrly quiet. My question is would the tank or the open bay be more suitable? Would the reflections of the calibration pulse make the tank more difficult to isolate the direct arrival? Or would the noise from the open bay make the tank set up more practical?

Answer 1

IMO, the glider calibration tank is far to small (narrow and not deep enough) for practical calibrations. I would go for the open sea calibration having the reference hydrophone at same distance (and geometry), i.e. very close to each other, then it should work.

To simplify procedure, I would transmit pulses of pseudorandom noise and compare the welch PSD, but you can also use tonal signal, but then the process last longer. Take only the initial part of the received signal, as there is very likely no multipath corrupting the signal. With tonals you can compare amplitudes.