WOBEC SOP Echosounder

Weddell Sea Observatory of Biodiversity and Ecosystem Change – WOBEC Standard Operating Procedures Technical Documentation December 2025 To be cited as Flores, Hauke, Nils Van den Steen, and Anton Van de Putte. ‘WOBEC SOP Echosounder’. Zenodo, 15 December 2025. https://doi.org/10.5281/zenodo.17935658. Co-funded by the European Union (c) The authors This report is licensed under the Creative Commons Attribution International license Versions Date Comment Responsible Approved First draft H. Flores 12/12/2025 Formatting N. Van den Steen Table of Contents 1 Description of sampling gear .......................................................................................................... 3 2 Sampling gear deployment .............................................................................................................. 3 2.1 Deployment ............................................................................................................................................. 3 2.2 Calibration ............................................................................................................................................... 4 2.3 Important preconditions: .................................................................................................................. 6 3 Sample sorting-collection-preservation procedure ............................................................... 8 4 Sample analysis method ................................................................................................................... 8 5 References .............................................................................................................................................. 8 6 Annex ........................................................................................................................................................ 9 Method responsible: Hauke Flores 1 Description of sampling gear This SOP applies to the under-way collection of hydroacoustic raw data for the estimation of abundance and biomass of krill and other macrozooplankton, and pelagic fish from vessels equipped with a ship-mounted split-beam echosounder. This SOP follows instructions of the CCAMLR WG-ASAM for hydroacoustic krill (Euphausia superba) surveys (CCAMLR 2023 and references therein), and of the MOSAiC expedition in the Central Arctic Ocean for hydroacoustic data collection of macrozooplankton and fish (Snoeijs-Leijonmalm 2021). [Schematic figure of echosounder] The specific instruments covered by this manual are limited to Simrad echosounders. However, devices from other manufacturers may be used if the technical specifications are comparable. Ideally, the hydroacoustic system consists of a hull-mounted split-beam echosounder capable of transceiving hydroacoustic backscatter signals at 38, 70, 120 and 200 kHz. 38 kHz is essential for estimating fish biomass, and the 70 and 120 kHz frequencies are needed for krill. Capability of the system to record data in broadband mode (fm) is desirable. The system should be connected to a GPS system with data output, and a data storage device capable of holding all raw data collected during one survey. Depending on the duration of the survey, frequencies used and the recording mode (single band, cw or broadband, fm), the typical storage capacity ranges between 2 TB (cw mode) and 20 TB (fm mode). 2 Sampling gear deployment 2.1 Deployment At the beginning of an expedition, the echosounder should be switched on in recording mode as soon as the vessel enters the WOBEC research area at Kap Norvegia or in the Kronprins Haakon VII Sea. Recording should be continuous until the ship leaves the WOBEC research area at the end of the expedition. Any other acoustic device (e.g. ADCP, Hydrosweep, OFOBS with sidescan sonar, Posidonia) should be switched off to avoid interference. If parallel operations of different hydroacoustic systems cannot be avoided, a syn- chronization device should be used, or raw data should be checked carefully to exclude or minimize data loss due to interference. During temporary actions involving other hydroacoustic devices, the echosounder may be paused. By standard, all data are recorded in cw mode (single frequency) and stored in raw format with UTC time stamp, applying the settings shown in Table x. Settings for recordings in fm mode (broadband) should be selected in such a way that single-frequency data extracted from the broadband data is comparable with genuine cw-mode data applying the settings shown in Table x. Table x: Instrument setting for data collection (CCAMLR 2023). Parameter Unit Setting Frequency kHz: 38 70 120 200 Power1 W 2000 700 250 110 Pulse duration Microsecond 1024 1024 1024 1024 Ping interval Second 2 2 2 2 Data collection range (min.–max.) M 0–1100 0–1100 0–1100 0–1100 Bottom detection range (min.–max.) M 5–1100 5–1100 5–1100 5–1100 Display range (min.–max.) M 0–1100 0–1100 0–1100 0–1100 1Based on Korneliussen et al. (2008) Vessels running EK80 or ES80 systems are encouraged to perform built-in self-test equipment (BITE – accessed through the diagnostics dialog box) diagnostics and provide the result by providing a screenshot of the test (Figure x). 2.2 Calibration The data recorded by the echososunder depends on the efficiency of the transducers under the ship. Because the transducer efficiency can be affected by the physical environment (temperature, salinity), and the aging of the system, the echosounder must be calibrated for every new field campaign in the environment in which it operates in order to maintain accuracy. The principle of the calibration is simple: a metal sphere with known material properties is moved around within the acoustic beam of each transducer while collecting data. A Tungtsen-Carbide sphere is appropriate for all frequencies mentioned in this SOP. By doing many measurements in the center of the beam and within the full beam we estimate potential offsets that can be used to adjust the raw readings of the echosounder into calibrated values. The standard procedure to carry out a sphere calibration is described in ICES (2015). In Simrad EK60 and EK80 systems, the calibration tool from the Simrad software used to control the software can be used (Figure x). For detailed instructions, see manual for Simrad Echosounder calibration (Annex 1). Figure x. Screenshot of the Simrad calibration software during calibration. Green dots show valid measurements within the sound beam. The center and all sectors of the beam must be evenly covered by measurements. 2.3 Important preconditions: For the calibration, the water movement relative to the ship must be minimal. Depending on the local conditions, the ship could be stabilized by anchoring in a sheltered zone (e.g., a fjord), or in “free drift” state in a deep-water area given the wind strength is not significant. It is also possible to perform the calibration when the ship is moored to an ice floe. To perform the calibration from an anchored ship, the water current must not be very strong, e.g., at the turn of tides. Further requirements are: • Water temperature and salinity similar to investigation area • Depth ≥ 50 m • enough ice-free space for free-floating operation, or near-zero currents for anchored operation • Ship is not actively moving • No crane operations • No bottom-sounding • Ideally, no thruster operations Maneuvering a ~2 cm sphere underneath a vessel can be challenging. Often, winch systems are used to position the sphere by adjusting the length of three wires attached to the sphere (e.g., Priou et al. 2020). Alternatively, a Remotely Operated Vehicle (ROV) can be used to position the sphere, e.g., from a moonpool (e.g. Snoeijs-Leijonmalm et al. 2022; Annex 2). The calibration procedure can take 6-12 hours, requiring adequate shiptime to be reserved when planning a hydroacoustic survey in an expedition. Table x (CCAMLR 2023). Instrument and calibration attributes recommended to accompany acoustic data submissions to the Secretariat (SC-CAMLR-42, Annex 4, Table 6). Operating frequency (kHz) Frequency of the transceiver / transducer combination in kHz. Some systems, such as broadband and multibeam, will have a range of frequencies. If so, specify the minimum, maximum and centre frequency Transducer location Location of installed transducer. Refer to ICES SISP 4-TG-AcMeta Appendix B.2 for a list of standard transducer locations Transducer manufacturer Transducer manufacturer Transducer model Transducer model Transducer depth (m) Mean depth in metres of transducer face beneath the water surface Transducer orientation Direction perpendicular to the face of the transducer. A simple description for a ship mounted sounder would be ‘downward-looking’, a mooring could be ‘upward-looking’. If required, ICES SISP 4-TG-AcMeta Appendix C provides a comprehensive description of transducer orientation conventions Transducer equivalent beam angle (dB) Manufacturer-specified transducer equivalent beam angle in dB, expressed as 10log10(Ψ), where Ψ has units of steradians Transducer beam angle major (degrees) Major beam opening in degrees, also referred to as ‘athwartship angle’. See ICES SISP 4-TG-AcMeta Appendix D for description of beam geometry conventions Transducer beam angle minor (degrees) Minor beam opening in degrees, also referred to as ‘alongship angle’. See ICES SISP 4-TG-AcMeta Appendix D for description of beam geometry conventions Transceiver manufacturer Transceiver manufacturer Transceiver model Transceiver model Transceiver serial Transceiver serial number Transceiver firmware version Transceiver firmware version Calibration date Date and time of calibration Calibration method Describe the method used to acquire calibration data (see ICES SISP 4-TG-AcMeta Appendix B.4, Standard lists) Calibration processing method Describe method of processing that was used to generate calibration offsets Calibration accuracy estimate Estimate of calibration accuracy. Include a description and units so that it is clear what this estimate means (e.g. estimate might be expressed in dB or as a percentage) Calibration location Name of the site where the calibration was carried out. Acquisition software name Name of software that controls the echosounder and its data logging Acquisition software version ersion of software that controls the echosounder and its data logging 3 Sample sorting-collection-preservation procedure Once the gear is back how is the sample collected, sorted and preserved (in a sense from deck to jar). Data should be stored in raw format in at least two copies: 1) on a local computer (e.g. the one running the Echosounder); 2) on an external hard drive. The recommended file size for storing acoustic data is 100 MB. Please record the instrument and calibration attributes before data collection (Table x). 4 Sample analysis method What analysis and addition measures are taken from the sample or from live specimen in case there are experiments or additional measures that are performed. Indicate the obtained parameters and units. After careful cleaning and post-processing (see SOP xx), data may be analyzed in terms of mean volume backscatter (Sv) or area-integrated backscatter strength (NASC), representing the relative distribution of abundance or biomass of krill, other macrozooplankton and/or fish. Careful validation with taxonomic and size data from net catches and/or eDNA data may enable calculation of absolute abundances and biomasses, based on certain assumptions (ref). Note that CCAMLR has so far not agreed on a standardized method to estimate krill biomass. 5 References Convention for the Conservation of Antarctic Marine Living Resources (2023) Report of the forty-second meeting of the Scientific Committee. CCAMLR, Hobart. 609 pp: Annex 4, 12, 13 Korneliussen RJ, Diner N, Ona E, Berger L, Fernandes PG (2008) Proposals for the collection of multifrequency acoustic data. ICES J. Mar. Sci., 65: 982– 994 International Council for the Exploration of the Sea (2015) Calibration of acoustic instruments. ICES Coop. Res. Rep., 326: 136 pp, doi:https://doi.org/10.17895/ices.pub.5494 Priou P, Nikolopoulos A, Flores H, Gradinger R, Kunisch E, Katlein C, Castellani G, Linders T, Berge J, Fisher JAD, Geoffroy M (2021) Dense mesopelagic sound scattering layer and vertical segregation of pelagic organisms at the Arctic-Atlantic gateway during the midnight sun. Progress in Oceanography 196: 102611 doi https://doi.org/10.1016/j.pocean.2021.102611 Snoeijs-Leijonmalm P (2021) Hydoracoustic data collection. In: SnoeijsLeijonmalm P (ed) EFICA Standard Operation Protocols for MOSAiC. Report to the European Commission. 36 pp Snoeijs-Leijonmalm P, Flores H, Sakinan S, Hildebrandt N, Svenson A, Castellani G, Vane K, Mark FC, Heuzé C, Tippenhauer S, Niehoff B, Hjelm J, Sundberg JH, Schaafsma FL, Engelmann R (2022) Unexpected fish and squid in the central Arctic deep scattering layer. Sci Adv 8: eabj7536 doi doi:10.1126/sciadv.abj7536 6 Annex 1. Calibration with EK 80 software (https://nextcloud.awi.de/s/eGJo3wzSPXL4KaQ) 2. Calibrating EK80 with an ROV (https://nextcloud.awi.de/s/ZLqDNbWZ3HiaWNm)