1 x imaging sonar and 2x sonar profilers. All within 25cm range of the triads. We couldn’t push the triads any further out as the system would be exceptionally unstable. Like using a donkey to steer an oil tanker. Our vehicle was rather small.
Axeman, it wasn’t quite so simple as that, we were operating sub 30Hz due to simops and noise passband of the other vehicle which was lead on the job. 60Hz AC was not an issue, neither were the harmonics.
We did pick up a lot of broadband ac/dc hum, probably from the switch mode supplies used onboard our vehicle, also from our thrusters which generated various amounts of noise (depending on rotor speed).
I was going on the presumption that the sonars have high torque rotation stages inside with high voltage piezo transducers on them. We couldn’t simply just go for a high threshold background subtraction as the signal to noise ratio was about 3:1 when we were sitting above the target (depth over 1.5m). Any lower and we just lost the cable because we couldn’t boost the signal either.
Killing the sonars and operating the dc thrusters at a frequency outwith our passband was the only way we could reduce the background noise in our passband. We managed to vastly improve our tracking. Target wobbed like hell with the sonars on.
We must have just been on the limit. Strictly speaking, SNR of 3.0 is normally the limit of detection for spectral analysis and peak detection.
Anyway, got the job done, but check your sonars just in case. It made a difference to us.
