This map shows Regional Cabled Array infrastructure at the summit of Southern Hydrate Ridge and the location of MARUM instruments, denoted by a 1 superscript. Credit: University of Washington.

The Southern Hydrate Ridge Overview Sonar (SHROS) was developed in 2017 by Dr. Yann Marcon, Professor. Gerhard Bohrmann, and a team of engineers at the MARUM Center for Marine Environmental Sciences and the Department of Geosciences, University of Bremen, Germany. It was funded by the German Federal Ministry of Education and Research (BMBF) within the scope of the “M³: Monitoring Marine Methane” projects (grants 03F0765A and 03F0854A). The SHROS monitors methane bubble plumes located within its 200 m range covering the entire Southern Hydrate Ridge summit.

The SHROS consists of a rotating multibeam echosounder mounted on a 3 m-high tripod (Figure 1). The echosounder is installed on top of a heavy-duty rotator with a rotation range of 360°, and is mounted on its side to orient the swath vertically and with a 45° tilt angle (Figure 2). With this setup, the volume of water that is scanned by a single 360° rotation of the sonar is equivalent to a half-sphere centered on the sonar and with a radius of 200 m. A processing unit located in a pressure vessel near the base of the instrument temporarily records the raw sonar data during the scans (up to 1Gbit/s) to prevent any data loss. The raw data are automatically downloaded at a maximum speed of 100Mbit/s to the NSF funded Regional Cabled Array PI network at the University of Washington after each scan.

The SHROS is scheduled to conduct one 360° scan of the water column every two hours. Each scan starts facing south (-180°) and rotates clockwise to +180°. During the bi-hourly scans, the sonar pings at a frequency of 350 kHz and a maximum pulse rate of 1 Hz. Depending on the scans, the pulse length settings vary between 70 µs and 560 µs. Depending on the needs, pinging frequencies ranging from 200 kHz to 450 kHz may also be used. The sonar can also ping at 700 kHz with a reduced swath opening.

Access OVRSRA101 Data

Instrument Models & Deployed Locations

The SHROS was installed near the center of the summit at Southern Hydrate Ridge at a water depth of 780 m. The instrument is connected to the medium- powered junction box MJ01B. It consists of a multibeam sonar (R2Sonic 2022), a heavy-duty titanium rotator (Sidus Solutions SS352), a data-logging computer in pressure housing, and a foldable tripod. The instrument control and data collection scheduling is run remotely on a shoreside computer located at the Regional Cabled Array Operation Center, University of Washington.

Reference Information

Data Format

Raw and processed PI instrument data for the SHROS can be accessed through via the following link http://piweb.ooirsn.uw.edu/marum/data/. Within the accessed ftp site, a read me text file provides information about data formats and instrument data. The data from the SHROS are provided both in raw and post-processed format. The raw data files (.wc) contain the water column data sent by the sonar in the form of binary packets. The format of the binary packets is described in the manufacturer's documentation (Sonic 2022-2024-2026 Operation Manual v6.3r000.pdf). The overview sonar produces a single raw data file for each scan. The size of a raw data file ranges between 0.8 GB and 20 GB, depending on the pulse length settings. The file naming includes the UTC starting time of the scan. Automated post-processing is applied to the raw data in order to facilitate the visualization of the gas emissions. The post-processing steps consist of filtering and clustering the magnitude data points (i.e. the intensity of the backscattered signal) to detect individual gas emissions. These steps are performed at the University of Bremen within 24 hours after data collection. The post-processing results are then pushed-back once a day to the OOI server. The data products include for each scan:
  • A raw data file (.wc) format (start time of the scan is in the filename),
  • A 3D image showing the bubble plumes detected in post-processing (Figure 3),
  • A HTML file documenting the UTC time of the scan, the sonar pinging frequency, the number of pings in the scan, the number of data samples in the scan, the estimated number and the average intensity of the bubble plumes that were detected during the scan. The intensity is expressed in terms of magnitude of the backscattered signal.
Publications related to the SHROS include: Marcon, Y., Kopiske, E., Leymann, T., Spiesecke, U., Vittori, V., Wahl, T. von, Wintersteller, P., Waldmann, C., Bohrmann, G., 2019. A Rotary Sonar for Long-Term Acoustic Monitoring of Deep-Sea Gas Emissions, in: Proceedings of the IEEE/MTS OCEANS 2019 Conference. Presented at the OCEANS 2019 - Marseille, pp. 1–8. https://doi.org/10.1109/OCEANSE.2019.8867218.