Acoustic and in-situ observations of stratified turbulent mixing near rough bathymetry in the Baltic Sea, Feb– Mar 2019 and 2020

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

This dataset contains acoustic midwater data from the Aland Sea, collected with a wideband Simrad EK80 sonar (70 kHz center frequency) during two cruises in February and March 2019 and 2020. Additionally, video visualisations of the acoustic midwater data are provided. Co-located with the acoustic broadband observations are in situ data from a free-falling microstructure profiler (MSS) from Sea&Sun Technology, ship Acoustic Doppler Current Profiler (ADCP) data that show current velocities in the upper 40 m of the water column and moored ADCPs showing the lower 100 m of the water column.

Midwater echo sounders permit remote observations of changes in the water column, including turbulence microstructure, thermohaline stratification, and suspended particles, as well as individual fish, fish schools, and zooplankton.

The microstructure profiler (MSS) provides oceanographic data from two shear probes (from which energy dissipation rates are inferred), two fast FP07 thermistors as well as conductivity, oxygen, turbidity, and depth.

Data were collected with R/V Electra.

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Data files

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Video previews

Citation

Julia C. Muchowski, Christian Stranne, Martin Jakobsson, Lars Arneborg, Lars Umlauf, Peter Holtermann (2023) Acoustic and in-situ observations of stratified turbulent mixing near rough bathymetry in the Baltic Sea, Feb– Mar 2019 and 2020. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/muchowski-2023-aland-sea-2019-2020-1

References

Muchowski, J. C., Jakobsson, M., Umlauf, L., Arneborg, L., Gustafsson, B., Holtermann, P., Humborg, C., & Stranne, C. (2023). Observations of strong turbulence and mixing impacting water exchange between two basins in the Baltic Sea. Copernicus GmbH. https://doi.org/10.5194/egusphere-2023-920

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 and therefrom derived processed data in the folder processed. Processed data are provided in the form of MATLAB mat structures. ADCP data are subdivided in data collected with R/V Electra's hull mounted ADCP (subfolder shipADCP) and additional ADCPs that were moored during the the two cruises (subfolder mooringADCP).

EK80 data are divided into data collected during EL19 and during EL20 due to their large size. In addition to the raw and processed EK80 data, we provide videos from both EL19 and EL20, in which we interpolated between EK80 data that were collected on the same transect. In total three videos are provided that are assets to the above referenced publication Muchowski et al. 2023.

The location of where the data was collected can be seen in the article by Muchowski et al. 2023 (Figure 1 therein).

Raw data

ADCP/shipADCP/raw

Ship 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.

ADCP/mooringADCP/raw

Mooring ADCP raw data files are named after the vessel used for deployment and recovering and the year of the cruise Electra2019_ADCP or Electra2020_ADCP. During EL20 two ADCP moorings were deployed, raw files therefore have the suffix _1 or _2. For each raw file, a .mat file with information about the raw data is in the same folder with the same name as the raw file and the suffix _rawinfo.

Raw files are provided as outputted by the instrument manufacturer Teledyne RDI software BBTALK.exe with file extension .000 and can be read and displayed using the WinADCP software. Detailed information can be found in the Teledyne Workhorse User's guide.

EK80/EL*/raw

EK80 raw data files have the date and time of the measurement as their filename in the form Dyyyymmdd-Thhmmss and are divided into subfolders for each day in the form yyyymmdd. 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 subfolders for raw and processed calibration data of the echosounder in the folders EL19/EL20_calibration_data, including the EK80 data as well as the data from the corresponding CTD cast.

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/raw

MSS raw data files are divided into files from EL19 and EL20 (subfolders MSS_EL19 and MSS_EL20, respectively). Files from EL20 are subdivided by the two MSS probes used during EL20 into folders MSS_probe_010 and MSS_probe_077. Files have the prefix E19 or 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 subfolders called processed in the form of MATLAB .mat structures with main content listed below. The Matlab structures also include other variables than those listed here.

ADCP/shipADCP/processed

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 (EL19), the ADCP hardware (600kHz), the temporal average of processed velocity data (5 s), the used reference velocity (refNone), and the transect during which the data were collected (T37). Data variables include:

• 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)

ADCP/mooringADCP/processed

The ADCP Matlab structures include the entire time series's collected with the moorings deployed during the time of the cruise duration in EL19 and EL20, as shown in the study by Muchowski et al. The filename includes additional information about the cruise (Electra2019/2020), the ADCP hardware (300 kHz), the temporal average of processed velocity data (60 s), and for the EL20 mooring also the number of the ADCP mooring (1 or 2). Data variables include:

• 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)
• sspd - sound speed velocity (m/s)

EK80/EL*/processed

Processed EK80 data files from EL19 are named by the start and end time of the measurement in the form YYYYMMDD_hhmm_hhmm and according to their general ID (transect_##) for all transects during the cruise. In addition, the file name includes information about the location of the transect (mostly standard - which means across the main sill that was studied), the amount of EK80 data before and after the first and last MSS cast collected on the transect (pad_05min) and the center frequency of the echosounder (70 kHz).

As an example: 20190226_0308_0345_transect_27_standard_EK80_pad_05min_70kHz

• transect number of the cruise: 27
• start time: 03:08 UTC
• end time: 03:45 UTC
  • 5 minutes of acoustic data before the first MSS cast and after the last MSS cast of the transect
  • 70 kHz center frequency

Processed EK80 data files from EL20 are named according to their general ID (transect_##) for all transects during the cruise 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
• start time: 16:45:06 UTC
• end time: 17:15:05 UTC

Data variables from both cruises include:

• range - depth below sea surface (m)
• echogram_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

Processed MSS data files from each cruise are all merged into one mat struct (MSS_all_EL19/EL20).

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

This dataset is used in Muchowski et al. (2023).