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High-resolution bathymetric mapping with the new broad-bandwidth, split- beam, scientific, multibeam sonar installed on the new NOAA FSVs G. R. Cutter.

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Presentation on theme: "High-resolution bathymetric mapping with the new broad-bandwidth, split- beam, scientific, multibeam sonar installed on the new NOAA FSVs G. R. Cutter."— Presentation transcript:

1 High-resolution bathymetric mapping with the new broad-bandwidth, split- beam, scientific, multibeam sonar installed on the new NOAA FSVs G. R. Cutter Jr. 1 D. A. Demer 1 L. Berger 2 1 NOAA NMFS Southwest Fisheries Science Center, La Jolla, CA 2 IFREMER, Département NSE, Plouzané, France.

2 NOAA ME70s NOAA FSVs Mount: ME70 transducer in centerboard Nav/Pos: POS/MV NOTE: SWFSC methods & IFREMER methods differ slightly but result in statistically the same FM bathymetry. Therefore, we present SWFSC results. Description and demonstration of seafloor characterization results available from ME70 (following methods developed for EK60) New NOAA Fisheries Survey Vessels (FSVs) –Oscar Dyson, Bigelow, Pisces, Shimada, FSV5, FSV6 –Equipped with the Simrad ME70 Quiet vessels (ICES spec.)

3 ME70 Scientific multibeam echosounder Developed by Simrad and Ifremer Principally designed for fisheries research Two operational modes: Fisheries Mode (FM) and Bathymetric Mode (BM) Either Mode –800 element array –Split-aperture processing for all beams –Motion-compensated to ±10° roll, ± 5° pitch, and heave –Calibration (by standard sphere) NOAA FSVs Mount: ME70 transducer in centerboard Nav/Pos: POS/MV NOTE: SWFSC methods & IFREMER methods differ slightly but result in statistically the same FM bathymetry. Therefore, we present SWFSC results. Description and demonstration of seafloor characterization results available from ME70 (following methods developed for EK60) ship ps -30°30° 0°

4 The configuration used for the calibration and SAT is: SAT Config 2. This config forms 17 beams in the fan, and 2 reference beams. The frequency of the beams in the fan range from 70 to 120 kHz. ME70 Operational Modes Fisheries mode FM –Records from entire water-column –USER-CONTROLLED CONFIGURATION: Number of beams (3 to 45) Beam directions, swath span and overlap Beam opening angles (min. 2°) Beam frequencies –WIDE-BAND ( kHz) frequency transmission –Two-way sidelobe suppression –Adjustable sidelobe levels (to -70 dB) –Calibrated S v, TS, and single target detections over entire water column –Depth estimation, by built-in amplitude bottom detection (with backstep) –Control and interface: ME70.exe software (We implement bottom-detection for FM data using amplitude and phase)

5 The configuration used for the calibration and SAT is: SAT Config 2. This config forms 17 beams in the fan, and 2 reference beams. The frequency of the beams in the fan range from 70 to 120 kHz. ME70 Operational Modes Bathymetric mode BM –Requires additional processor machines (bathymetric module) –FIXED CONFIGURATION Equidistant or equiangle beams, *2 possible pulse options. 80 narrow beams (up to 200 soundings per swath) Beams formed during reception One-way sidelobe suppression (-35 dB) –SINGLE FREQUENCY transmission –Bottom-detection using amplitude near normal-incidence and phase for more oblique angles –Control and interface: Standard Simrad EM processor station and SIS software (as for EM series multibeams) –BM is like a typical seafloor-mapping multibeam Integrates ancillary data, and produces.ALL format files.

6 NOAA FSVs –ME70s with Fisheries Mode only Q1 - In addition to water-column fisheries survey data, can the ME70 FM provide bathymetric data for hydrographic or habitat studies? –For this, we need FM mode to deliver: High-resolution bathymetry, comparable to BM & standard MBES Backscatter data for seafloor characterization Q2 - Do we really need the BM? This study: derives and compares bathymetry collected with and without the bathymetric processor unit (BM & FM) NOAA ME70s NOAA FSVs Mount: ME70 transducer in centerboard Nav/Pos: POS/MV NOTE: SWFSC methods & IFREMER methods differ slightly but result in statistically the same FM bathymetry. Therefore, we present SWFSC results. Description and demonstration of seafloor characterization results available from ME70 (following methods developed for EK60) Quiet vessels (ICES spec.)

7 ME70 Flowchart.ALL Files Bathymetric Mode (fixed configuration) SIS work station Hydrographic-data processing software (e.g. Caris HIPS, Hypack) IMUGPSCT Seabed bathymetry and classifications.RAW Files ME70 workstation Simrad ME70 Custom software Fishery Mode (custom configuration) Fishery-data processing software (e.g. Movies 3D, Echoview) Animal classifications, abundances, distributions, and 3D images

8 France + Survey Area * Survey Thalassa See Ifremer articles for vessel and equipment details, Or get from L. Berger. Particularly, Nav/Pos ME70_Ifremer_UTM_OverviewMap.png ME70 on blister on hull Pic in Berger paper Date: 19 March 2008 Vessel: R/V Thalassa Survey speed: ~10 knots (BM) Conducted by Ifremer Bay of Biscay, west of France R/V Thalassa –Currently, the only vessel with ME70 with FM & BM

9 >250 m >240 m >230 m Common coverage betw BM and FM Study Range setting for FM used during survey of data4: 232 m Comparisons using ME70 data collected in bathymetric and fisheries mode from overlapping coverage Range setting for FM: 232 m Show swath with depth > range Common coverage from BM and FM Drop these?

10 Bathymetry from Bathymetric Mode Processing of Simrad ME70 Bathymetry Mode data using CARIS HIPS Import.ALL Remove outliers (editor or filter) Examine motion data Apply tide Merge Create surface Export Notice the few bad detections from sidelobes, Auto-removed by filter. BM Bathymetry –Standard hydrographic data processing methods and software: CARIS HIPS Only gross outliers were removed –Other options: Ifremer software, Hermes, Movies3D, and perhaps Hypack, or Triton

11 Bathymetry from Fishery Mode SWFSC Estimation of Depth from ME70 FM.RAW files z corr (t) = z u (t) + z tdcr + heave(t) – z tide (t) Trigonometric solutions for local x’,y’ and then conversion to global coordinates E, N  E, N, z Tdcr zθzθ r θ  z θ θ rθrθ Heave from the IMU and Tdcr depth are recorded in the raw file. Theta(a) is recorded in the raw file (beam direction, compensated for motion). Range r(θa) is estimated from a bottom-detection method using amplitude or phase; converted to uncorrected depth (z_u); then corrected for transducer depth, heave, and tide, giving corrected depth (z_corr); and its associated local horizontal coordinate values (x,y) are converted to global values (E, N; UTM Zone 30 north). Tdcr θaθa seafloor r(θ a ) zuzu Tdcr depth heave z tide Revise fig w/ swath where sf is not so flat, And aligning the ray with an actual beam Post-proc tools for ME70 FM data are lacking, so we have to implement ourselves. This bucket is your ship. The orange Tdcr is the sonar transducer.... The tdcr transmits a pulse of sound. It travels through the water and reflects or scatters off organisms, density interfaces, and the seafloor, and some of it travels back to the receiver, We use the time of travel to estimate the range to the targets (in this case the sf); that is r(theta_a) where theta_a is the angle of arrival. We know the angle of arrival for each formed beam, and use that to estimate the depth relative to the tdcr (giving z_uncorrected) If we know tdcr depth, heave (we do), and estimate water elevation due to tide (we did), then we can compensate for those, resulting in an estimate of corrected depth, by beam direction and time, z_corrected(t,beamdir). FM Bathymetry –Custom Matlab code –Other options: Myriax Echoview, Ifremer software –Depth estimation: Not compensated for refraction

12 Center of mass of e or S v –Differs from peak if noisy Bottom detection Amplitude e or S v Differential phase Alternatives –CUBE (Calder et al.) –Bayesian model including amplitude and phase information from several beams and transmissions (Bourguignon et al., 2009) –More robust phase-differencing (Demer et al. 2009) Clarify What BM uses, What Ifremer uses, What SWF uses * S v (dB) Thr Range (m) Show waves arriving at 2 tdcrs That allow phase diff meas θ°θ°

13 Seafloor grid models (5 by 5 m grid cell size) from FM Zpzc and BM ZBM plotted using identical colormaps. Soundings Sounding locations resulting from ME70 BM & FM Mean depth in this subregion: 220 m FM: 21 beams, each ~ 3° BM: 80 beams –Up to 200 soundings per ping –(~150 soundings per ping with valid bottom detections for this dataset) Number of soundings per 10 by 10 m grid cell, for a) BM, and b) FM. # per 10-m cell 100 m

14 Note In BM, the ME70 swath spans 120° In FM, the user specifies the swath span for the ME70 …or wider For this study, the ME70 swath span in FM was chosen to be 60°.

15 FM ampl FM ampl&phase BMFM Bathymetry Results

16 BM FM Depth (m) Comparison Perspective view from NW Interpolated surfaces –FM (ampl. detect only) Explain the two datasets, the viewpoint, The colorscale and interval, the similarity, and differences, Replace FM results from phase-detection only With FM results from combined ampl/phase detec. If outer beam artifacts apparent, show a swath where depth > range. Maybe, enhance boundaries in 3d ? Diffs for normal inc beams and where bottom exceeded range (outer beams in deep water) Explain the two datasets, the viewpoint, The colorscale and interval, the similarity, and differences, Replace FM results from phase- detection only With FM results from combined ampl/phase detec. If outer beam artifacts apparent, show a swath where depth > range. Differences are practically zero

17 Depth (m) Comparison Perspective view from NW Interpolated surfaces –FM (ampl. & phase detect) Explain the two datasets, the viewpoint, The colorscale and interval, the similarity, and differences, Replace FM results from phase-detection only With FM results from combined ampl/phase detec. If outer beam artifacts apparent, show a swath where depth > range. Maybe, enhance boundaries in 3d. Diffs for normal inc beams and where bottom exceeded range (outer beams in deep water) BM FM Differences are practically zero

18 % Difference Difference BM – FMpzc_with_outliers % difference in depth between BM and FM grids ME70_comparisons_BMtc-FMpzctc.png Path: C:\Cutter\ME70\Collaboration\IFREMER\GIS\map_images Measured diffs Betw BM, FM grids -0.5 to +1 m Difference BM – FM pSv Comparison

19 Difference BM – FMpzc_with_outliers Comparison Difference in depth between BM and FM grids Green: -0.5 < dz < 0.5 m Mean difference: -0.5 to +1.5 m for a depth range from 200 to 230 m Overall mean difference (SD): 0.58 (0.40) m Differences may be due to refraction or tide ME70_comparisons_BMtc-FMpzctc.png Path: C:\Cutter\ME70\Collaboration\IFREMER\GIS\map_images Measured diffs Betw BM, FM grids Calc proportion of diffs. Maybe Combine with previous slide -0.5 to +1 m dz (m), BM-FM Difference BM – FM pSv but not stationary

20 Seafloor slope BM FM

21 Seafloor roughness BMFM

22 Depth (m) Seafloor backscatter FM Calibrated Seafloor BS (from FM) Sv  Ss Normalized for slope Map of FM BS. Plot of BS vs Slope BM DN Note outline of FM on BM Ss (dB)

23 Seafloor classification Roughness & hardness index from backscatter and seafloor slope –See: Demer et al ICES J. Mar. Sci, 66. SSID Demer et al. (2009) Relies on incidence angle of each beam

24 Conclusions Accurate and precise bathymetry can be obtained from ME70 operating in FM and BM –BM – FM: dz 95% of the common coverage area –Differences were < 0.25% for more than 40% of the common coverage area –By accounting for refraction, using alternative bottom detection methods, for FM solutions differences could be reduced Possible limitations of FM –Reduced ping rate –Reduced number of beams Some new methods have promise to overcome these limitations –Lack of post-processing software Advantages of FM –Two-way beamforming and lower sidelobe levels –Water-column data –Multiple-frequencies Do we need the Bathymetric Mode? –Consider the quality of FM bathymetry –Resources for FM data processing could be a better investment Accurate and precise bathymetry can be obtained from ME70 operating in FM and BM Differences between bathymetry surfaces from BM and FM* were 90% of the common coverage area Differences were < 0.25% for more than 40% of the common coverage area By accounting for refraction for FM solutions differences could be reduced Possible limitations of FM Reduced ping rate Reduced angular span of the swath Reduced number of beams Some new methods have promise to overcome these limitations Lack of post-processing software Advantages of FM Two-way beamforming and lower sidelobe levels Water-column data Multiple-frequencies Do we need the Bathymetric Mode?


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