Acoustic and in-situ observations of stratified turbulent mixing over rough bathymetry, Baltic Sea, March 2020

Julia C. Muchowski, Christian Stranne, Martin Jakobsson, Lars Arneborg, Lars Umlauf, Peter Holtermann

This dataset contains broadband acoustic midwater data, ship acoustic doppler current profiler (ADCP) data, and in situ microstructure profiler (MSS) data from the Åland Sea, Baltic Sea. The dataset was collected with research vessel R/V Electra af Askö in 2020 and was used with a focus on turbulence measurements.

The acoustic data were collected with a hull-mounted broadband Simrad EK80 sonar (70 kHz center frequency). Midwater echo sounders permit remote observations of turbulence microstructure, but also more generally changes in the water column, its stratification and suspended particles, as well as individual fish, fish schools, and zooplankton. Ship ADCP data were collected with a hull-mounted 600 kHz Teledyne RDI Workhorse ADCP.

The co-located in situ data were collected with a free-falling microstructure profiler (MSS) and include high-resolution oceanographic data from two shear probes (from which energy dissipation rates are inferred), two fast FP07 thermistors as well as conductivity and depth data.

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Data files

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Citation

Julia C. Muchowski, Christian Stranne, Martin Jakobsson, Lars Arneborg, Lars Umlauf, Peter Holtermann (2023) Acoustic and in-situ observations of stratified turbulent mixing over rough bathymetry, Baltic Sea, March 2020. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/muchowski-2023-midwater-2020-1

References

Muchowski JC, Arneborg L, Umlauf L, Holtermann PL, Eisbrenner E, Humborg C, Jakobsson M, Stranne C (2022) Diapycnal Mixing Induced by Rough Small-Scale Bathymetry. Geophysical Research Letters (in review).

Data description

The data are provided in folders ADCP,EK80, MSS, named after the instruments. We include the collected raw data in the sub-folder raw.zip and therefrom derived processed data in the folder processed. Processed data are provided in the form of MATLAB mat structures.

The location of where the data was collected can be seen in the article by Muchowski et al. (their Figure 1).

Raw data

ADCP

ADCP raw data files have the prefix ADCP and a running number in their file name. Several file extensions are included as outputted by the instrument manufacturer software Teledyne RDI VmDas:

• .ENR: raw current velocity (ADCP) data, current velocity data in beam coordinates.
• .ENS: .ENR data with navigational data from NMEA, current velocity data in beam coordinates.
• .ENX: content of .ENS files transformed from beam to earth coordinates using NMEA heading, pitch, roll, as well as bin-mapped, screened for error velocity, and false targets.
• .STA: short time average.
• .LTA: provide long time average.
• .N1R: .NMS ASCII NMEA files.
• .VMO: option settings for collecting the ADCP data.
• .LOG: text file with instrument log, including beam width, beam direction, and time stamps.

NMEA data is fed from the positioning system on the ship into the ADCP raw files and provides the real time coordinates of the vessel.

.ENR, .STA, and .LTA files can be read and displayed using the WinADCP software. Detailed information can be found in the VmDas User's guide.

EK80

EK80 raw data files have the date and time of the measurement as their filename in the form Dyyyymmdd-Thhmmss. Note that the time stamp in the file name comes from computer time on the data acquisition PC and may differ from the GPS time stored in the actual raw data. EK80 raw data consist of the following file types:

• .raw: measurement data
• .idx: index files
• .XYZ: files that contain longitude, latitude, depth, and time. The .XYZ files have the following additional information about the transducer in their filename: ES70-7CSerialNo0.

NMEA data is fed from the positioning system on the ship into the EK80 raw files and provides the real time coordinates of the vessel.

In the EK80 data folder, we also included a subfolder for raw data of the calibration of the echosounder in the folder calibration_data, including the EK80 raw data (subfolder EK80-raw) as well as raw and preliminary processed CTD data (subfolder CTD_calibrationEK80.zip).

EK80 raw files can be opened and visualized with e.g. the instrument manufacturer Simrad EK80 software as well as the python based ESP3 software (open source), and Echoview (commercial).

MSS

MSS raw data files have the prefix E20 and a running number in their file name. File extension is .MRD. File format is according to SSDA Sea & Sun Technology's Standard Data Acquisition software package rev. 228 28.06.2018.

Processed data

Processed data are provided in the form of MATLAB .mat structures with main content listed below. The matlab structures also include other varables than those listed here.

ADCP

The ADCP Matlab structure includes only data that were collected on a subset of the data, used in the study by Muchowski et al. The filename includes additional information about the cruise (EL20), the ADCP hardware (600kHz), the temporal average of processed velocity data (30s), the used reference velocity (refNone). Data variables include:

• u - current velocity east-west (m/s)
• v - current velocity south-north (m/s)
• curr - complex double, current velocity east-west (m/s) (real part) and south-north (m/s) (imaginary part)
• rtc - time (UTC) in MATLAB datenum format
• depth - depth bin mid-point (m)
• lat - latitude (decimal °N)
• lon - longitude (decimal °E)
• nvel - navigation velocity (m/s)
• bottom - seafloor depth as measured with ADCP bottom track function
• sspd - sound speed velocity (m/s)

EK80

Processed EK80 data files are named according to their general ID (transect_##) for all transects during the cruise, their region and transect number (SRUL#), followed by the start and end time of the measurement in the form Thhmmss_Thhmmss.

As an example: transect_27_SRUL7_T164506_T171505

• transect number of the cruise: 27
• transect in the specific sub-region: 7
• start time: 16:45:06 UTC
• end time: 17:15:05 UTC

Data variables include:

• range - depth below sea surface (m)
• Sv - volume backscatter (dB)
• lat - latitude (decimal °N)
• lon - longitude (decimal °E)
• time - time of the measurement (UTC)
• transceiver - technical information about the hardware and hardware settings

MSS

Processed MSS data files are named according to the date, start, and end time when they were collected (yyyymmdd_hhmm_hhmm) and their station number (MSS_station_###).

Each Matlab structure has four components:

• MSS.STA: station information, including
  • LON - longitude
  • LAT - latitude
  • GPSTime - GPS time
  • date - date
  • fname - filename of raw data file
• MSS.DATA: raw data from raw data file, including
  • T - temperature
  • C - conductivity
  • P - pressure
  • SH1 and SH2 - shear probe measurements
  • Vsink - sinking velocity of the profiler
  • rawO2 - oxygen
• MSS.CTD: 0.1 m resolution data, including:
  • P - pressure (dbar)
  • T - temperature (°C)
  • CT - conservative temperature (°C)
  • S - salinity from (g/kg)
  • SA - absolute salinity from (g/kg)
  • O2 - uncalibrated oxygen (O2)
  • Turb - uncalibrated turbidity
  • SIGT - water density minus 1000 (kg/m³) calculated with the TEOS-10 Gibbs Sea Water toolbox
  • N2 - buoyancy frequency (1/s²) calculated with the TEOS-10 Gibbs Sea Water toolbox
• MSS.MIX: 0.5 m resolution data, including:
  • P - pressure (dbar)
  • eps - dissipation rate of turbulent kinetic energy (W/kg)
  • N2 - buoyancy frequency (1/s²) calculated with the TEOS-10 Gibbs Sea Water toolbox
  • Vsink - sinking velocity of the profiler (m/s)

Comments

The following table links transects (T1⁠ – ⁠T6) that are analyzed in the study by Muchowski et al. to the microstructure (MSS ) profiles that were collected during those transects. Each transect has a number that is related to the total number of transects during the cruise (T21⁠ – ⁠T27) and a number that only takes into account transects within a sub-region (with acronym SRUL) of the study area (T1⁠ – ⁠T7). All data were collected during R/V Electra cruise EL20-IGV01 in 2020.