Acoustic and in-situ observations of stratified turbulent mixing in the Baltic Sea, February 2019

Julia Muchowski, Christian Stranne, Martin Jakobsson, Lars Umlauf, Lars Arneborg, Peter Holtermann, Elizabeth Weidner

This dataset contains broadband acoustic midwater data, ship and mooring 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 2019 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. Mooring ADCP data were collected with a 300 kHz Teledyne RDI Workhorse ADCP.

The free-falling microstructure profiler (MSS) measurements provide 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.

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Data files

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Citation

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

References

Muchowski, J., Umlauf, L., Arneborg, L., Holtermann, P., Weidner, E., Humborg, C., & Stranne, C. (2022). Potential and Limitations of a Commercial Broadband Echo Sounder for Remote Observations of Turbulent Mixing. Journal of Atmospheric and Oceanic Technology, 39(12), 1985–2003. https://doi.org/10.1175/jtech-d-21-0169.1

Data description

The data are provided in folders EK80, MSS, shipADCP, mooringADCP, 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.

The location of where the data was collected can be seen in the article by Muchowski et al. 2022, in Figure 1.

Raw data

shipADCP/raw

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.

mooringADCP/raw

One mooring ADCP raw file is provided with the name Electra2019 and file extension .000 , as outputted by the instrument manufacturer software Teledyne RDI VmDas. The file can be read and displayed using the WinADCP software. Detailed information can be found in the VmDas User's guide.

EK80/raw

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 EK80, including the EK80 raw data (subfolder raw) as well as raw and preliminary processed CTD data (subfolder Electra190222083353_EL19-IGV01_CTD02).

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 have the prefix el19 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 variables than those listed here.

shipADCP/mat

The ADCP Matlab structure includes only data that were collected on a subset of the data, used in the study by Muchowski et al. Data variables include:

• u_corr_rot - rotated and corrected current velocity east-west (m/s) - which was corrected using navigation speed and multiplied by a factor of 1.2 due to a shield mounted under the transducer with a refraction index different to that of water.
• v_corr_rot - rotated and corrected current velocity south-north (m/s) - corrected the same way as u_corr_rot
• time - time (UTC) in MATLAB datenum format
• depth - depth bin mid-point (m)
  • times_48h - start and end time of continuous measurements of the transect across the sill

mooringADCP/mat

The Matlab structure Electra2019_ADCP_300s_val.mat contains processed and over 300 s averaged mooring ADCP data. 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)

EK80/mat

Processed EK80 data files are named by the date, start and end time of the measurement in the form yyyymmdd_hhmmss_hhmmss, followed by their general ID (transect_##) for transects used in Muchowski et al. (2022), followed by the location of the transect (mostly standard which refers to a transect across the sill shown in Fig. 1 in Muchowski et al. (2022)) and followed by general information about the instrument (70 kHz EK80) and the amount of acoustic data included before and after MSS casts taken on the transect (pad_05min - refers to 5 minutes of acoustic data before the first MSS cast and after the last MSS cast of the transect).

As an example: 20190226_0808_0905_transect_32_standard_EK80_pad_05min_70kHz.mat

• date: 26 February 2019
  • start time: 08:08 UTC
  • end time: 09:05 UTC
  • transect number of the cruise: 32 Data variables 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/mat

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)