• NEANIAS Underwater Research Community

Die luftgestützte Laser-Bathymetrie ist eine Fernerkundungstechnik zur Kartierung der Unterwassertopographie. Im Vergleich zum topographischen Airborne-Laserscanning ist die Lichtausbreitung in zwei Medien zu berücksichtigen. Ein wichtiger Unterschied besteht auch darin, dass für den Einsatz in der Bathymetrie nur Wellenlängen des Lasers im sichtbaren Bereich verwendet werden können, da Licht im Infrarotbereich praktisch nicht in das Wasser eindringen kann. Die erste Generation von Scannern für die Bathymetrie kam kurz nach der Erfindung des LASERS zum Einsatz. Während anfangs hauptsächlich nur analoge Elektronik für die Auswertung der Signale zur Verfügung stand, wurde später die gesamte Kurvenform des rückgestreuten Echos digital aufgezeichnet. Das Aufkommen erschwinglicher Computer öffnete schließlich den Weg zu komplexerer Signalverarbeitung.Für die Bestimmung der Elevation des Unterwasserbodens ist es notwendig, zwei signifikante Zeitpunkte in der Wellenform zu identifizieren. Der erste ist der Zeitpunkt, zu dem der Lichtimpuls ins Wasser eintritt und der zweite der Zeitpunkt, zu dem er auf den Boden trifft. Es ist von besonderer Bedeutung, den ersten Moment zu kennen, denn von diesem Moment an bewegt sich der Impuls langsamer und in eine andere Richtung.Die Standardmethode zur Identifizierung eines Zeitpunkts in einem Signal ist die Gauß’sche Zerlegung des Signals. Unter Wasser leidet die Methode jedoch unter dem Problem, dass viele verteilte kleine Partikel Störechos verursachen, die die genaue Zerlegung behindern. Solange die Verteilung solcher Teilchen nicht zu dicht ist hat die Wellenform exponentiellen Charakter. In dieser Arbeit stelle ich daher ein Modell vor, das aus Exponentensegmenten besteht, die die Wirkung der Teilchen beschreiben, und Dirac-förmigen Impulsen, die die Wirkung diskret angeordneter Streuer beschreiben. Diese Beschreibung ist jedoch noch nicht ausreichend, um die empfangene Signalform zu erklären. Das Exponentialmodell muss mit der Systemwellenform gefaltet werden, um eine korrekte Darstellung des empfangenen Signals zu erhalten. Durch Minimierung der Differenz zwischen dieser Darstellung und den gemessenen Daten können die Parameter des Exponentialmodells erhalten werden. Ich stelle eine Prozedur vor, die ich Exponentialzerlegung nenne, mit der die eigentliche Verarbeitung durchgeführt werden kann. Die Wirksamkeit des Verfahrens wird auf der Grundlage von Daten überprüft, die in einem Nebenfluss der Donau gesammelt wurden. Anhand von mittels GNSS-vermessenen Kontrollpunkten wird die Richtigkeit der Ergebnisse bestätigt.Ein wichtiger Aspekt bei der Modellierung von Signalen ist, dass das Modell physikalisch korrekt ist. Ein unterschätzter Effekt in der Laser-Bathymetrie ist, dass sich gepulstes Licht langsamer ausbreitet als herkömmlich angenommen. Da der Effekt im Zusammenhang mit der Laser-Bathymetrie noch nicht diskutiert worden ist, beschreibe ich ein von mir durchgeführtes Experiment, das den Effekt in seiner vorhergesagten Größe bestätigt. Darüber hinaus befasse ich mich mit den Fragen, ob ein Ein-Wellenlängensystem realisierbar ist und was die kleinste messbare Tiefe in der Laser-Bathymetrie ist. Airborne laser bathymetry is a remote sensing technique for the mapping of underwater topography. Compared to topograhic airborne laser scanning, light propagation in two media must be considered. An important difference also is that for use in bathymetry, only wavelengths of the laser in the visible range can be used, since light in the infrared range is practically unable to penetrate the water. The first generation of scanners for bathymetry came into use shortly after the invention of the LASER. Although in the beginning mainly only analog electronics was available for the evaluation of the signals, later the entire trace of the backscattered echo was recorded digitally. The advent of affordable computers finally opened the way to more complex signal processing.For the determination of the elevation of the underwater bottom it is necessary to identify two significant time instants in the waveform. The first is when the light impulse enters the water and the second is when it hits the bottom. It is especially important to know the first moment, because from this moment on the impulse moves slower and in a different direction.The standard method to identify an instant of time in a signal is by gaussian decomposition of the signal. Underwater, however, the method suffers from the problem that a lot of distributed small particles cause clutter that is hindering the exact decomposition. For a tenuous distribution of such particles the waveform is of exponential character. In this thesis I therefore introduce a model consisting of exponential segments that describe the effect of the particles and Dirac shaped pulses that describe the effect of discretely located scatterers. This description is however not sufficient yet to account for the received signal form. The exponential model has to be convolved with the system waveform to yield a correct representation of the received signal. By minimizing the difference of this representation and the measured data the parameters of the exponential model can be retrieved. I present a procedure, which I call exponential decomposition, by which the actual processing can be done. The effectiveness of the procedure is verified on the basis of data collected in a tributary of the Danube river. The correctness of the results is confirmed using GNSS surveyed control points.An important aspect for the modeling of signals is that the model is physically correct. An underestimated effect in laser bathymetry is that pulsed light propagates more slowly than conventionally assumed. Since the effect in the context of laser bathymetry has not yet been discussed, I describe an experiment I performed that confirms the effect in its predicted magnitude. Furthermore, I deal with the questions whether a single wavelength system is feasible and what the smallest measurable depth in laser bathymetry is.

Multibeam bathymetric data were acquired during R/V SONNE Cruises SO104, SO244, and R/V Marcus G. Langseth Cruise MGL1610. The datasets were individually processed and gridded with grid cell sizes of 75 m. For the combined grid, depth information from SO244 was used wherever possible. If no SO244 data were available, MGL1610 data were preferred over SO104 data. The backscatter data were collected during R/V SONNE Cruise SO244. For processing of the backscatter information, all data recorded during turns of the ship were eliminated before gridding to a 20 m cell size throughout the study area.

This dataset contains bathymetry (depth) products from the compilation of all available source bathymetry data within Northern Australia into a 30 m-resolution Digital Elevation Model (DEM). The Northern Australia region includes a broad continental shelf over 400 km wide extending out from Western Australia and the Northern Territory, and stretching over a distance of ~1500 km. This region encompasses numerous shallow coral reefs including the offshore Sahul Banks, sand cays, drowned ancient river valleys, broad inner-shelf banks and a rugged coastline. Bathymetry mapping of the seafloor is vital for the protection of Northern Australia, allowing for the safe navigation of shipping and improved environmental management. Shallow- and deep-water multibeam surveys have revealed the highly complex seafloor of the continental shelf and adjacent slope canyons draining into the Indian Ocean and Timor Sea. Airborne LiDAR bathymetry acquired by the Australian Hydrographic Office cover most of the Sahul Banks reefs, with some coverage gaps supplemented by satellite derived bathymetry. The Geoscience Australia-developed Intertidal Elevation Model DEM improves the source data gap along Northern Australias vast intertidal zone. All source bathymetry data were extensively edited as point clouds to remove noise, given a consistent WGS84 horizontal datum, and where possible, an approximate MSL vertical datum.

Bathymetric data was collected using a hull-mounted 1° x 1° EM122 Multibeam Echo Sounder (MBES). The EM122 equipment was operated using Kongsberg Seafloor Information System (SIS) and Helmsman software. Where possible, data were collected in a systematic manner with survey lines running parallel along depth contours to achieve consistent swath coverage and maximise insonification of slope areas. Sound velocity profiles (SVPs) were generated from CTD casts and applied during data acquisition. Additional information about the data acquisition can be found in the cruise reports. The data processing was performed using the QPS Qimera software. Tide gauges used: Station| IOC ID |Type |Logging Interval Roth (Sheldon Cove) | ID: 342 |Radar |1 min Vern (Borgen Bay)| ID: 188 | Pressure|1 min Prat3 (Marian Cove) | ID: 189 | Pressure / Radar| 1 min Tide gauge data: http://www.ioc-sealevelmonitoring.org/ Coordinates are in WGS84 UTM projected coordinates: Sheldon Cove:19 S Borgen Bay:20 S Marian Cove:21 S We present three new gridded bathymetric compilations of Sheldon Cove, Börgen Bay and Marian Cove. These bathymetry grids were compiled from EM122 multibeam swath bathymetry data acquired during three different cruises (RRS James Clark Ross JR17001, JR18003 and JR19002 cruises also known as NERC-ICEBERGS cruises) from 2017 to 2020. The data is available as grids of 5 m resolution in NetCDF and GeoTIFF formats using geographic coordinates on the WGS84 datum. This grid was compiled as part of the ICEBERGS (Impacts of deglaciation on bentic marine ecosystems in Antarctica) project. Funding was provided by the NERC grant NE/P003087/1. Data processing was performed in QPS Qimera software using observed tide from local tide stations. Gross errors were removed manually prior to each dataset being processed individually using filters and additional manual editing in problem areas. Total Propagated Uncertainty and data density were checked prior to merging successive years into the final product. Depths relate to mean depth of all surveys and refer to chart datum at each respective tide gauge. Data is NOT TO BE USED FOR NAVIGATION. Data were collected as part of the following RRS James Clark Ross cruises: - JR17001 in 2017 - JR18003 in 2018 - JR19002 in 2020

Australia has established a network of 58 marine parks within Commonwealth waters covering a total of 3.3 million square kilometres, or 40 per cent of our exclusive economic zone (excluding Australian Antarctic Territory). These parks span a range of settings, from near coastal and shelf habitats to abyssal plains. Parks Australia manages the park network through management plans that came into effect for all parks on 1 July 2018. Geoscience Australia is contributing to their management by collating and interpreting existing environmental data, and through the collection of new marine data. Eco-narrative documents are being developed for those parks, where sufficient information is available, delivering collations and interpretations of seafloor geomorphology, oceanography and ecology. Many of these interpretations rely on bathymetric grids and their derived products, including those in this data release.

Australia has established a network of 58 marine parks within Commonwealth waters covering a total of 3.3 million square kilometres, or 40 per cent of our exclusive economic zone (excluding Australian Antarctic Territory). These parks span a range of settings, from near coastal and shelf habitats to abyssal plains. Parks Australia manages the park network through management plans that came into effect for all parks on 1 July 2018. Geoscience Australia is contributing to their management by collating and interpreting existing environmental data, and through the collection of new marine data. Eco-narrative documents are being developed for those parks, where sufficient information is available, delivering collations and interpretations of seafloor geomorphology, oceanography and ecology. Many of these interpretations rely on bathymetric grids and their derived products, including those in this data release.

Australia has established a network of 58 marine parks within Commonwealth waters covering a total of 3.3 million square kilometres, or 40 per cent of our exclusive economic zone (excluding Australian Antarctic Territory). These parks span a range of settings, from near coastal and shelf habitats to abyssal plains. Parks Australia manages the park network through management plans that came into effect for all parks on 1 July 2018. Geoscience Australia is contributing to their management by collating and interpreting existing environmental data, and through the collection of new marine data. Eco-narrative documents are being developed for those parks, where sufficient information is available, delivering collations and interpretations of seafloor geomorphology, oceanography and ecology. Many of these interpretations rely on bathymetric grids and their derived products, including those in this data release.

The bathymetry map was compiled from a variety of different data sources. The primary data are multibeam swath bathymetry collected from scientific cruises undertaken by British Antarctic Survey (BAS) but also German and US cruises. The complete list of the cruises used for the compilation is the following: -RRS James Clark Ross: JR287, JR17004 -RRS Discovery: DY100 -RV MARIA S. MERIAN: MSM20/2 and MSM24 -RV Melville: MV1203 -RV Knorr: KN145L17 The grid was created using the mbgrid program from MB-system version 5.7.6, using the parameters " -E0.001/0.001/degrees! -G4 -A2 -F1 -R-16.8/-5/-43.5/-33" for the Arc/Info and ArcView ASCII grid and " -E0.001/0.001/degrees! -G3 -A2 -F1 -R-16.8/-5/-43.5/-33" for the netCDF file (GMT version 2 GRD file) . This uses a Gaussian weighted mean filter. Bathymetry data is gridded as topography (positive upwards). We present a new gridded bathymetric compilation around Tristan da Cunha here defined by the following bounding box: 5 to 16.8W, 33 to 43.5S. This bathymetry grid was compiled from a variety of multibeam swath bathymetry data acquired during 7 different cruises (see lineage). The data is available as a grid of 0.001 degrees resolution in three different formats: NetCDF, ArcView ASCII and GeoTIFF formats using geographic coordinates on the WGS84 datum. This grid is an output of the UK FCDO 'Blue Belt' program and the following Natural Environment Research Council (NERC) BAS-ODA fundings: NE/R000107/1 and NE/T012439/1. The data has been processed using different software including CARIS and MB-system. Final quality control was undertaken manually to remove any outliers in the source datasets. This involved cleaning much of the raw data using the "mbedit" program from MB-system. Data collected from the following cruises: -RRS James Clark Ross: JR287, JR17004 -RRS Discovery: DY100 -RV MARIA S. MERIAN: MSM20/2 and MSM24 -RV Melville: MV1203 -RV Knorr: KN145L17

The multibeam swath bathymetry data were collected on scientific cruises undertaken by British Antarctic Survey (BAS) on RRS James Clark Ross: JR53-AMT11, JR287, JR15001 and JR16-NG. The grid was created using the mbgrid program from MB-system version 5.5.2336, using the parameters " -E0.0005/0.0005/degrees! -G4 -A2 -F1 -R-14.57/-14.17/-8.12/-7.75" for Arc/Info and ArcView ASCII grid and " -E0.0005/0.0005/degrees! -G3 -A2 -F1 -R-14.57/-14.17/-8.12/-7.75" for the netCDF file. This uses a Gaussian weighted mean filter and the bathymetry is gridded as topography (positive upwards) We present a new bathymetric compilation around Ascension Island here defined by the following bounding box: 14.57 to 14.17 W, 8.12 to 7.75 S. This bathymetry grid was compiled from a variety of multibeam swath bathymetry data acquired during 4 different cruises (see lineage). The data is available as a grid of approximately 50 m resolution in two different formats: a GMT-compatible (2-D) NetCDF and Arc/Info and ArcView ASCII grid format using geographic coordinates on the WGS84 datum. Quality control was undertaken manually to remove any outliers in the source datasets. This involved cleaning much of the raw data using the "mbedit" command from MB-system.

The bathymetry map was compiled from a variety of different data sources. The primary data are multibeam swath bathymetry collected from scientific cruises undertaken by British Antarctic Survey (BAS), or acquired during RV Nathaniel B. Palmer, RV Surveyor, RV Maurice Ewing and RRS James Cook expeditions. The complete list of the cruises used for the compilation is described below: James Clark Ross expeditions: JR59, JR69-67, JR71, JR81, JR84, JR93, JR112, JR115, JR149, JR150, JR158, JR179, JR185, JR188, JR193-196, JR194-197, JR228, JR230, JR233, JR239-235-236, JR240, JR244, JR252-254c, JR254D-264-265, JR255A, JR276, JR279-286, JR281, JR299, JR306-307, JR312, JR15003, JR16002, JR16003, JR17003, JR17003A Ewing cruise: EW9101 James Cook cruises: JC055, JC054 NB Palmer cruises: NBP9507, NBP9902, NBP9903, NBP9904, NBP9905, NBP0001, NBP0002, NBP0003, NBP0106, NBP0107, NBP0201, NBP0202, NBP0502, NBP0602A, NBP0603, NBP0606, NBP0703, NBP0710, NBP0805, NBP0908, NBP1001, NBP1003, NBP1103, NBP1105, NBP1107, NBP1203, NBP1304, NBP1602, NBP1603, NBP1608 Surveyor cruises: AMLR95, RITS93A, RITS94B, AMLR90, AMLR92, AMLR94 The grid was created using the mbgrid program from MB-system version 5.5.2336 , using the parameters " -E0.001/0.001/degrees! -G4 -A2 -F1 -R-63/-53.3/-63.50/-60.5" for Arc/Info and ArcView ASCII grid and " -E0.001/0.001/degrees! -G3 -A2 -F1 -R-63/-53.3/-63.50/-60.5" for the netCDF file. This uses a Gaussian weighted mean filter and the bathymetry is gridded as topography (positive upwards) We present a new bathymetric compilation of the South Shetland Islands here defined by the following bounding box: 63 to 53.3 W, 63.5 to 60.5 S. This bathymetry grid was compiled from a variety of multibeam swath bathymetry data acquired during 76 different cruises (see lineage). The data is available as a grid of approximately 100 m resolution in two different formats: a GMT-compatible (2-D) NetCDF and Arc/Info and ArcView ASCII grid format using geographic coordinates on the WGS84 datum. The grid contains both raw and processed data.