Free-Rising Microstructure Profiler in Full-Water-Column of Ocean

Turbulent mixing within a few meters near the ocean surface and bottom plays a crucial role in air-sea and sea-solid interactions, but it is often under-sampled due to observational challenges. To address this issue, the Free-rising Full-water-column Microstructure Profiler (FFMP) has been developed to perform the microstructure measurement in full water depth under an undisturbed condition. FFMP has a spherical shape and possesses the advantages of low fluid resistance, minimal disturbance, and easy operation. The main sensor package on FFMP includes fast-response thermistors (FP07), conductivity-temperature-depth (CTD), acoustic trans-ducer, three-dimensional (3D) inclinometer, and acceleration. In the in-situ application, the FFMP attached with a disposable iron anchor is deployed from the ship deck downwelling to the sea floor. After making sure that the FFMP arrives on the sea floor, the acoustic signal from the ship is sent to release it by dropping off the anchor. The FFMP rises freely through the whole water column, meanwhile, the full-water-column microstructure signals are recorded. Turbulent dissipation rate is inferred based on the theoretical spectral analysis of the microstructure data. On the sea surface, the FFMP transmits radio signals to facilitate location for recovery. The FFMP has been tested in the South China Sea with the water depth ranging from 28 to 3095 m, and the results are verified to be consistent with those of the commercial free-falling microstructure profiler.