The 3-hourly CTD observation at the fixed station is for listening to the various voices in the ocean.
The sea water in the surface layer of 0-30 m depth sings with the sun and the moon joins below 80 m depth.
Someone probably should join in the chorus in lower voices behind them.
The high-frequency operation is necessary so that the observation should catch the various melodies.
Qoosaku MOTEKI
YMC Blog 