Buoy-mounted Acoustic Doppler Current Profiler Research Articles

Improved Current Estimates from Spar Buoy-Mounted ADCP Measurement Station: A Case Study in the Ligurian Sea

Current measurements in the open sea are generally acquired by Acoustic Doppler Current Profilers (ADCPs). In the case of ADCPs mounted on spar buoy, current profiles require to be post-processed, to properly take into account the buoy influence: in fact, ADCP compass may reflect alterations induced by the metal structure of the buoy and apparent currents can occur due to the large displacement of the platform. Uncertainty analysis is finally required to properly consider both these effects and to compute robust velocity estimates. A new methodology is tested for a measurement station in the Ligurian Sea, where an ADCP was mounted on the surface buoy of the W1-M3A (Western 1 Mediterranean Moored Multisensor Array) oceanographic observatory, facing upwards at the depth of about 40 m. Marine current numerical models and historical data in the area have been used as a basis for comparison to test the consistency of the proposed method. A very good agreement is obtained. Only minor discrepancies are reported (e.g., monthly averages from the reference model slightly underestimate the west-east current component along the entire profile), but, in general, the application of the proposed methodology ensures that the spar buoy-mounted ADCP system is able to provide reliable measurements for oceanographic studies and validation of 3D hydrodynamic models.

Low frequency current variability on the shelf break northeast of Taiwan

A buoy-mounted Acoustic Doppler Current Profiler was deployed on the shelf break off the northeast coast of Taiwan to monitor current variations in the upper ocean. The acquired data show that the flow in the upper water column was initially southwest and then abruptly turned northwest. This abrupt change occurred in mid-October, starting from the surface layer and then gradually extending to the deeper layer. In contrast with this flow, the flow in the lower water column was southwest over the entire record, but its amplitude was reduced after the middle of October. The abrupt change of current from southwest to northwest is related to the intrusion of Kuroshio. Examination of two CTD casts showed the salinity of the upper ocean to have increased after the directional shift in mid-October, further indicating the Kuroshio intrusion. The sea level data at Keelung provided other evidence for the intrusion of Kuroshio. The sea level descended as the intrusion occurred and kept the low value until the end of the record. The northwest flow, which carried the water away from the northern coast of Taiwan, is responsible for this descent. Although the intrusion of Kuroshio was mainly confined to the upper ocean, it did have influence on the whole water column. Examination of the wind record at Pengchiayu showed that the time of Kuroshio intrusion was not coincident with the intensification of the northeasterly monsoon. The local wind and the current at 20 m were incoherent. Both the variation of Kuroshio current and the fluctuation of Kuroshio path may be responsible for the variation of the local current. Since the intrusion of Kuroshio has a weak relationship with local wind variation, it appears to be induced by non-local factors.

Effects of a Thermistor String Mounted between the Acoustic Beams of an Acoustic Doppler Current Profiler

Abstract A useful extension of upward-looking buoy-mounted acoustic Doppler current profilers (ADCPs), in particular for studying surface-mixed-layer dynamics from underneath, would be to combine them with a thermistor cable for obtaining simultaneous current and temperature profiles. Measurements with an ADCP, operating at 150 kHz and sampling at 2.2 m vertical bin lengths, were carried out from a barge moored in Lake San Vincente, California, over a water depth of 45 m, to investigate the effects of a thermistor string running along the axis of the instrument between the acoustic beams and held by a small auxiliary float. The biasing effect of the thermistor string itself was only of order 1%. Doppler biasing of the horizontal currents by two different kinds of Coats (one a cylindrical hard foam float with low acoustical reflectivity, the other a hollow sphere) was investigated. The floats were suspended at 15 and 30 m. For floats at 30 m, evidence was not conclusive because of apparent interference by ...

87:6047 Half-year-long measurements with a buoy-mounted acoustic Doppler current profiler [ADCP] in the Somali current: Schott, Friedrich and William Johns, 1987. J. geophys. Res., 92(C5):5169–5176

87:6047 Half-year-long measurements with a buoy-mounted acoustic Doppler current profiler [ADCP] in the Somali current: Schott, Friedrich and William Johns, 1987. J. geophys. Res., 92(C5):5169–5176