Kopte, Robert; Achterberg, Eric Pieter (2025): Shipboard ADCP current measurements (75 kHz) during RV MARIA S. MERIAN MSM130 [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.980750

Current velocities of the upper water column along the cruise track of R/V Maria S. Merian cruise MSM130 were collected by a vessel-mounted 75 kHz RDI Ocean Surveyor ADCP. The ADCP transducer was located at 6.0 m below the water line. The instrument was operated in two different configurations: 1) broadband mode (WM1) with a bin size of 8.00 m, a blanking distance of 8.00 m, and a total of 100 bins, 2) narrowband mode (WM10) with a bin size of 8.00 m, a blanking distance of 8.00 m, and a total of 100 bins. The covered depth range was 22.0 m to 814.0 m. Attitude data from the ship's motion reference unit were used by the data acquisition software VmDAS internally to convert ADCP beam velocities to geographic coordinates. The Python toolbox OSADCP (version 2.0.0) was used for data post-processing. Single-ping data were screened for bottom signals and, where appropriate, a bottom mask was manually processed. Acoustic Interferences were identified based on outliers in the ADCP echo intensity data. Echo intensity data were cleaned accordingly and affected velocity cells were flagged to be removed prior ensemble-averaging. The ship's velocity was calculated from position fixes obtained by the Global Navigation Satellite System (GNSS), taking into account lever arms of ADCP transducer and GNSS antenna. Accuracy of the derived water velocities mainly depends on the quality of the position fixes and the ship's heading data. Further errors stem from a misalignment of the transducer with the ship's centerline. Data processing included water track calibration of the misalignment angle (configuration 1: -47.2542° +/- 0.5410°, configuration 2: -47.2217° +/- 0.7196°) and scale factor (configuration 1: 0.9983 +/- 0.0095, configuration 2: 0.9973 +/- 0.0134) of the measured velocities. The velocity data were averaged in time using an average interval of 120 s (configuration 1) and 60 s (configuration 2). Depth cells with ensemble-averaged percent-good values below 25% are marked as 'bad data'. Furthermore, the time series of cell 1 to 4 (configuration 1) and cell 1 to 6 (configuration 2) are flagged as 'potentially correctable bad data' because of velocities biases most likely caused by transducer ringing.