Schneider von Deimling, Jens

OceanRep

  Cruise Report RV Littorina  LIT/1907 (11.06.2019 – 14.06.2019)   Hydroacoustic assessment of the seagrass Zostera marina with modern multibeam echosounding in the Geltinger Bucht and the Kolberger Heide        Jens Schneider von Deimling (University Kiel)  June 2019   Scientific Crew  Research programme The cruise was carried out as part of the European joint project BONUS ECOMAP, coordinated by the CAU. The aim of the research&development project ECOMAP is to significantly improve the remote sensing of different habitats in the Baltic Sea and therefore to better understand the underlying control mechanisms and the environment. Various optical and acoustic methods are currently being developed for this purpose. For LIT1907 a NORBIT multibeam echosounder was optimized for the mapping of submarine vegetation. We here focus on the seagrass Zostera marina which is known for its large potential in terms of longer term CO2 storage in the sediment, for being a nursery ground for fish, for mitigating coastal erosion, and even for improving the water quality. The interested reader is referred to related work in ECOMAP, which is dedicated to seagrass assessments in the Baltic Sea (www.bonus-ecomap.eu).  Cruise narrative Tuedsay, 11th of June: Embarking the vessel, installation of the multibeam via the Littorina pole, steaming to Geltinger Bucht, calibration of the motion reference unit. RTK operated unstable via a radio connection. First multibeam survey lines were run including a roll calibration which was measured to -0.21°. Moderate wind and sea state during this day. Wednesday, 12th of June: Achieving permanent RTK fix with a cabled ethernet solution to the ships mobile connection. Continuation of surveying the shallow parts of the Geltinger Bucht between 3 and 7 meters. Groundtruthing by video and grab sampling. Calm weather and sea state. Thursday, 13th of June: Continuation of surveying the shallow parts of the Geltinger Bucht between 3 and 7 meters. Survey along the east coast off Damp to Boknis Eck along the 5 m contour line. Transit to the Kolberger Heide in the late afternoon and subsequent survey during the night. Surveying transect lines normal to the coastline from 5 m to 10 m water depth with a line spacing of about 420 m, to derive maximum growing depth of Zostera Marina in the main EcoMap test area. Calm weather. Name Affiliation FunctionJens Schneider von Deimling CAU Cruise LeaderPhilipp Held CAU HydroacousticsFlorian Gausepohl CAU HydroacousticsFlorian Weinberger GEOMAR BiologieMeghan Troup Dalhousie University HydroacousticsFriday, 14th of June: Completion of the profile lines normal to the coastline. Then several lines were sailed approximately parallel to the coast over the found maximum growth depths of Zostera Marina. Sailing one test line with the new STX-Modus of the Norbit MBES. Subsequently, groundtruthing with underwater video and grabs at locations marked during the MBES measurements. Finally, calibration profiles were run for the MBES. Transit back to Kiel. Figure 1: Overview over the recorded MBES data during cruise L1907, with zooms into the main research areas: Geltinger Bucht and the main EcoMap test area at Kolberger Heide off Heidkate.     Scientific report and first results The Geltinger Bucht and a transect from Kalkberg to Boknis Eck were selected as the first working areas with the focus on the 5 m depth contour line and the acoustic detection of the seagrass Zostera Marina thereon. Afterwards, mapping of the seagrass in the Kolberger Heide continued to assess the maximum depth of occurrence as a baseline study. Both study sites are known to be populated by Zostera marina (Schubert et al. 2015).    Fig. 2: (left) perspective view on a multibeam echosounder point cloud spanning a few meters showing Zostera marina as depth anomalies (orange) in the Geltinger Bucht (b) adjacent patch where each sounding is color-coded by uncompensated backscatter amplitude also redrawing the seagrass distribution. Sonar is known to be sensitive to seagrass, but there is no consensus of the ideal system yet (Gumusay et al., 2019), and many unsolved questions remain from a bio-acoustic point of view. We here present data from a novel and very promising approach.  We sailed our survey lines with 3.5-4.5 knots. The prototype NORBIT STX was operated at 400 kHz with 80 kHz bandwidth sending out a 150° swath angle 20-35 times a second. Therefore we achieved very dense point cloud data with more than 80 soundings per square meter. The system was  calibrated before with spheres in an acoustic test basin by our project partner NORBIT. The sonar parameters were fine-tuned to achieve a best performance for detection of submerged aquatic vegetation (SAV), afterwards we kept the sonar parameters constant to make the data comparable throughout the survey. CTDs were taken to later correct for sound refraction and absorption effects and also to evaluate temperature, salinity, pH, O2 saturation, and sound velocity of the water column. The multibeam system performed very well and we achieved high quality point cloud data in the centimeter (vertical) to decimeter (horizontal) positioning accuracy that are prone for our automatic detection of seagrass (Held and Schneider von Deimling, 2019). In the Geltinger Bucht seagrass was acoustically detected in depths between ca. 3-6 m, exact depth values will be available after postprocessing. Fig. 2 shows both, the characteristic depth anomalies redrawing the seagrass canopy height, and the beam backscatter intensity amplitude being indicative for seagrass. The acoustic interpretation of Fig. 2 was validated by video and grab samples both showing Zostera marina growing on a well-sorted fine sand (Fig. 3).   Fig. 3: Video still shot showing Zostera marina growing on sand. Sediment samples were sieved for grain size analyzes and collected for later analyses of total organic carbon onshore. Other acoustic anomalies were found in in the Bay (Grab01-04), but here, groundtruthing showed the existence of appr. 10 cm high algae (Ceramium) in a poorly sorted sediment with silty sand to gravel grain sizes.   The succeeding survey from Kalkberg to Boknis Eck along the shoreline in 5 m water depth was designed to detect stones ~0.5 m, which are known to occur in this area. From an acoustic perspective, rocks of such size present a possible candidate to be confused with Zostera marina showing typically a canopy height of similar magnitude during this time of the year. Overall, the acoustic signatures between the two candidates appear visually very diverse and are most likely discernable after re-training of our data-driven, machine learning classification model (Held and Schneider von Deimling, 2019).  The Kolberger Heide area was acoustically surveyed for seagrass in 2017 and a maximum water depth of occurrence of Zostera was determined at 7.5 m below sea level in a Msc thesis (Lübmann, 2018). Next to seagrass occurrences the seabed here is characterized by sand and sorted bedforms like sandbars along the shoreline as well as ripple structures. The ripples and the acoustic seagrass anomalies are well visible in the snippet multibeam backscatter data (Fig. 4), plotting similar to sidescan, but providing precise geolocation of the backscattered signals. Characteristic patterns of Zostera are elevated backscatter at near-nadir often occurring in a patch-like manner. Towards the outer beams the backscatter remains high, but dedicated shadowing effects occur. Beyond the outer beams the snippet sidescan data often extend in a blurry manner with elongated sonar travel time, which we interpret as multipath effects between seagrass canopy-canopy and/or canopy-seafloor acoustic interaction.      Fig.: 4: Multibeam echosounder snippet backscatter data showing (left) ripples and seagrass. Across distance is around 10 m, bright colors indicate high acoustic energy. (right) sand ripples and a few stones with prominent acoustic shadows similar to sidescan imagery.  To map out the maximum depth of Zostera marina on a larger extent we performed in-and-out surveying with lines perpendicular to the coastline every 400 meters within the depth interval of 5-10 m. Therein, the maximum depth occurrence of Zostera was mapped out (Fig. 1).     Scientific equipment and sampling  Multibeam: NORBIT iWBMS prototype STX with 400 kHz center frequency. Survey settings were fixed to Static Gain: 6 dB; Spreading: 40 dB/km; Absorption: 75 db/km (T=15, S=16, @ 5 m  75.2 dB, after Ainslie); Backscatter mode: snippets/scan; F: 400kHz, Mode: FM deep; range res. 0.9 cm; ping rate adaptive, up to 35 Hz; Adaptive gates: off; roll/pitch stab.: off; Pulse amp.: 15; beam distr. Equiang. 512; multidetect, on max sens. upper/lower on. Data were recorded as .wbm and .s7k via NORBIT Version 10.4FW5.1., and in parallel as .db and .qpd with Qinsy 8.18.3 (ETRS 89, GCG2016). Intertial Navigation and motion reference unit: Applanix Wavemaster provided with Axio Net RTK RTCM 3.1 correction with ID#15 (ETRS 89, GCG2011). CTD: Sea and Sun Technology CTD60M, equipped with a Pt 100 temperature sensor, a pressure sensor of type PA7-10, a cylindrical 7 electrode conductivity sensor, an oxygen sensor of type AMT-DO and a PH sensor of type AMT-pH.  GoPro: GoPro Hero3. Video settings: wide angle, 1080p and 24 fps; additionally, every 3 s a still shot with 24 Mpx. Underwater camera: towed live-view camera, equipped with a CMOS image sensor with 100 TV lines. Van-veen-grab Acknowledgements We highly acknowledge the expertise of captain Volkmar Marks and his crew and appreciate their great support throughout the cruise with RV Littorina. This work resulted from the BONUS ECOMAP project, supported by BONUS (Art 185), funded jointly by the EU and the Federal Ministry of Education and Research of Germany (BMBF), the National Centre for Research and Development of Poland (NCBR), and the Innovation Fund Denmark (Innovationsfonden). We also appreciate the free use of the RTK service kindly provided by the AXIOnet GmbH. The authors would also like to thank the German Federal Maritime and Marine Hydrographic Agency BSH, and the environmental authorities LLUR, and LKN.SH for knowledge exchange and continuous support of ECOMAP. References Gumusay, M.U.; Bakirman, T.; Tuney Kizilkaya, I.; Aykut, N.O. A review of seagrass detection, mapping and monitoring applications using acoustic systems. Eur. J. Remote Sens. 2019, 52, 1–29. Held, P., & Schneider von Deimling, J. (2019). New Feature Classes for Acoustic Habitat Mapping—A Multibeam Echosounder Point Cloud Analysis for Mapping Submerged Aquatic Vegetation (SAV). Geosciences, 9(5), 235. Lübmann, 2018. Hydroakustische Untersuchung der Seegraswiesen in der Kolberger Heide. Msc thesis Geophysics, University Kiel.  Schubert, P. R., Hukriede, W., Karez, R., & Reusch, T. B. (2015). Mapping and modeling eelgrass Zostera marina distribution in the western Baltic Sea. Marine Ecology Progress Series, 522, 79-95.   Stationbook   Date/UTCStation[#]GearLocationLat []Long []Water depthCommentGrab table11.06.2019St 1MBES TransitSt2CTD1, O2 1Geltinger BuchtSt3MBES SurveyGeltinger Bucht12.06.201906:10St4CTD02Geltinger Bucht506:50St5Grab01-1Geltinger Bucht54:46.5809:52.92152 pictures taken #107:04Grab01-2Geltinger Bucht54:46.5809:52.92152 pictures taken #207:11St6Grab02Geltinger Bucht54:46.6049:52.963with St# in photo#307:20MBES TransitGeltinger Buchtnow with RTK via Eth0 Brücke08:00St7Grab03Geltinger Bucht54:47.7989:47.999with video#408:03St8Grab04-01Geltinger Bucht54:47.9249:48.015leer08:07Grab04-02Geltinger Bucht54:47.9249:48.015sand, kies, steine , Algenaufwuchs#508:15MBES TransitGeltinger BuchtTRK fix08:53St9MBES Roll CalibGeltinger Bucht54:46.7769:53.637to N, 3.5kn09:01MBES Roll CalibGeltinger Buchtto S, 3.5kn09:14St10CTD03Geltinger Bucht54:46.7429:53.60309:23St11MBES surveyGeltinger Bucht4-5 knots09:50MBES surveyGeltinger Buchtstrong noise, restart10:01MBES surveyGeltinger Buchtback to survey10:20MBES surveyGeltinger Buchtadjacent survey line12:27MBES surveyGeltinger Buchtnow without MD13:23MBES surveyGeltinger Buchtnow without WCI14:29St12Video startGeltinger Bucht54:47.7319:53.730tow track GoPro14:44Video stopGeltinger Bucht54:47.5889:53.693tow ende14:49St13MBES video validationGeltinger Bucht14:58St14Grab 05Geltinger Bucht54:47.7479:53.745validate Zostera ground; 5 pictures taken#613.06.2019Geltinger Bucht06:05St15CTD04Geltinger Bucht54:47.84109:53.2101006:10St16MBES surveyGeltinger BuchtWCI on, MD on06:5506:55WCI res set to highest for 1 line07:24Test ELAC record 1 line10:07St17CTD05Ostküste Pottloch54:44.43509:59.65012:08giant stone site13:29St18CTD06Boknis Eck54:32.79910:02.64216:06St19CTD07Kollberger Heide54:27.31710:17.43310O2 Kalib Schwankung +-10 %16:29St20MBES Roll CalibKollberger Heide1016:42Ende Roll calibSt21Survey ZigZagKollberger Heide14.06.201902:25St22Survey Max Depth zosteraKollberger Heidestandard setting02:32Pockmark?02:42UXO?06:28St23Yaw CalibKollberger Heide06:52St24Drop Camera 01Kollberger Heide54:26.52610:20.232stones overgrown with algae; sparse seagrass occurrences on more sandy parts07:05St25Drop Camera 02Kollberger Heide54:26.56810:20.615sandy bottom; frequent ripple occurrences; some seagrass, only individual stalks; high amount of mussels/mussel shells07:16St26Drop Camera 03Kollberger Heide54:26.47410:20.812some dense seagrass patches; sandy bottom; few rocks with algae07:32St27Drop Camera 04Kollberger Heide54:26.78810:20.246sandy bottom; frequent overgrown cobbles; some shell fragments07:52St28Drop Camera 05Kollberger Heide54:27.48610:18.605sparse seagrass occurrences (individuals; 3-5 leaves); sandy; shell fragments; benthic life (Ostracoda) and Lebensspuren08:08St29Drop Camera 06Kollberger Heide54:27.09310:17.850sandy bottom; frequent seagrass occurrences; shell fragments; benthic life (Ostracoda) and LebensspurenSt30Drop Camera 07Kollberger Heide08:36St31Grab06Kollberger Heidewith full res WCI, seagrass with 0.8m length, fine sand, turning anoxic#708:54St32MBES STX testKollberger HeideSTX scan on09:06St33MBES Pitch calib forthKollberger HeideSTX scan off09:13pitch backKollberger Heide_______________________________CTD (Weinberger) h UTC+2h 10 minMBES has timeUTCScreenshots has timUTCWater level at lighthouse Kalkgrund   Water level time series from wsv for later RTK height validation (WSV).   Wind conditions during the survey:  Screenshots from www.windfinder.de 11.06.2019: Station Kegnæs Fyr    12.06.2019 station Kegnæs Fyr:     13.06.2019 Station Schönhagen    station Kieler lighthouse   14.06.2019  Station Kieler lighthouse  

Cruise Report R.V. Littorina, Cruise No.: L19/07 [L19-07]:

Cruise Report RV Littorina LIT/1907

(11.06.2019 – 14.06.2019)

Hydroacoustic assessment of the seagrass Zostera marina with modern multibeam echosounding in the Geltinger Bucht and the Kolberger Heide

http://oceanrep.geomar.de/46977/1/Lit1907_Fahrtbericht_zostera_final.pdf

Cruise Report R.V. Littorina, Cruise No.: L19/07 [L19-07]: Cruise Report RV Littorina LIT/1907 (11.06.2019 – 14.06.2019) Hydroacoustic assessment of the seagrass Zostera marina with modern multibeam echosounding in the Geltinger Bucht and the Kolberger Heide

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