The Impact of Acoustic Imaging Geometry on the Fidelity of Seabed Bathymetric Models

Attributes derived from digital bathymetric models (DBM) are a powerful means of analyzing seabed characteristics. Those models however are inherently constrained by the method of seabed sampling. Most bathymetric models are derived by collating a number of discrete corridors of multibeam sonar data. Within each corridor the data are collected over a wide range of distances, azimuths and elevation angles and thus the quality varies significantly. That variability therefore becomes imprinted into the DBM. Subsequent users of the DBM, unfamiliar with the original acquisition geometry, may potentially misinterpret such variability as attributes of the seabed. This paper examines the impact on accuracy and resolution of the resultant derived model as a function of the imaging geometry. This can be broken down into the range, angle, azimuth, density and overlap attributes. These attributes in turn are impacted by the sonar configuration including beam widths, beam spacing, bottom detection algorithms, stabilization strategies, platform speed and stability. Superimposed over the imaging geometry are residual effects due to imperfect integration of ancillary sensors. As the platform (normally a surface vessel), is moving with characteristic motions resulting from the ocean wave spectrum, periodic residuals in the seafloor can become imprinted that may again be misinterpreted as geomorphological information

An Efficient Workflow and Accuracy Assessment for ICESat-2 and Multispectral Imagery Fusion for Bathymetric Mapping

Interest in mapping bathymetry from multispectral satellite imagery has grown steadily since the 1970s. Notwithstanding the significant advancements made during this time, one limitation is that the group of algorithms collectively referred to as Satellite Derived Bathymetry (SDB) generally require “seed depths,” hindering their use for areas lacking reliable reference data. Recently, NASA’s ICESat-2 ATLAS, a satellite-based, photon counting green lidar, has been shown capable of bathymetric mapping. Although ICESat-2 bathymetry is constrained to discrete tracklines, synergistic fusion of ICESat-2 and multispectral, passive imagery can generate contiguous bathymetry over large spatial extents. Despite these significant recent results and the possibilities they open for filling shallow nearshore data voids worldwide, significant challenges remain, including: 1) ICESat 2/multispectral imagery fusion techniques are still in the early research stage and not efficient enough for widespread operational use for the average user, and 2) detailed, empirical accuracy assessments of fusion-based bathymetric products generated through operationally-efficient workflows have not been conducted. This research addresses these gaps. A highly-efficient workflow is developed and tested for generating bathymetric DEMs for large areas through largely-automated retrieval and fusion of ICESat-2 photon clouds and multispectral imagery, with the outputs disseminated via a webGIS. Empirical accuracy assessments are performed in two locations, selected to encompass vastly differing environmental conditions. One is a freshwater, inland water site where airborne imagery was used, while the other is a tropical, coastal saltwater site, covered by Landsat 8 and Sentinel-2 data. The workflow is shown to be operationally efficient and capable of producing bathymetry of sufficient accuracy for many coastal science applications, with RMSEs for the two sites being 0.95 m for Lake Tahoe (σ = 0.89 m, μ = 0.34 m) and 0.80 m (Sentinel-2; σ = 0.77 m, μ = -0.19 m) and 1.42 m (Landsat 8; σ = 1.19 m, μ = 0.77 m) for St. Croix

Journal of Applied Hydrography

Fokusthema: Fernerkundung und Laserbathymetri

Conception and realisation of a photogrammetric multisensor system for an uncrewed water vehicle

Due to climate change, extreme weather events and their effects like flash floods have become more frequent in recent years, causing major damages to landscapes and infrastructure, and endangering human lives. This is one of the reasons why it is desirable to monitor rivers and fluvial processes. Besides gauging water levels and flow velocities, it is necessary to know the morphology of the river as precisely as possible. In hydrodynamic flood modelling, for example, high-resolution river models are needed for a prediction of the flooded areas. By comparing the river profile before and after a flood event, conclusions can be drawn about changes in the landscape. River surveys need to record both, the banks above the water level, and the river bottom below the water level. This dissertation presents the conception and implementation of a photogrammetric multisensor system on an uncrewed water vehicle (UWV). It proofs that a well-equipped UWV is a useful measurement system for recording the topography of rivers above and below the water level providing relevant information about the river morphology. For deriving accurate 3D information above the water level, a camera and a mobile lidar are attached to the platform. For the bathymetric measurement of the river profile, a single beam echo sounder is initially used. The individual sensors record data in different coordinate systems. For a combined model of the river, these measurements need to be fused in one coordinate system. Therefore, a calibration method is presented that enables the determination of the relative orientations between all sensors. Lidar measurements provide detailed information about the riverbanks. Since the sensor is used on a moving platform, georeferencing of the lidar points is a crucial issue of the method. Thus, position and orientation of the scanner must be known during the entire acquisition. This is usually solved with an inertial navigation system (INS), consisting of an IMU (inertial measurement unit) and a GNSS (global navigation satellite system) receiver. However, due to shadowing from vegetation on the banks and multipath effects from the water surface, satellite positioning is likely to be error prone on rivers. IMUs are furthermore influenced by electric fields on the small platform, resulting in drifts in the orientation determination. Therefore, an independent method for determining the position and orientation of the platform is developed. For this purpose, time-lapse images of the camera on the UWV are used. Their orientation is determined with photogrammetric multi-image methods. Based on a relative orientation between the camera and the scanner coordinate system, these orientations are used for georeferencing the lidar points. This calibration method enables a fast and highly accurate determination of the relative orientation. For the monitoring of the river bathymetry, the UWV carries a single beam echo sounder. However, echo sounding has principal limitations in shallow waters. This issue can be solved with a laser triangulation sensor combining the contrary properties of both sensors. Laser triangulation enables highly accurate line scans in close range applications and is an established method in optical industrial surveying. In order to use the method for underwater measurements, the sensor system, consisting of a camera and a laser line projector, must first be placed in a waterproof glass housing. The lightsheet emitted by the laser line projector is then refracted several times at the interfaces from air to glass and from glass to water. A method for the exact modelling and calibration of these ray paths is presented. In addition, the accuracy potential is evaluated in a theoretical assessment. In practical tests, which were first carried out in the laboratory, the previously estimated submillimetre accuracy was confirmed. The results of the previously presented methods offer approaches for further developments. A comparison of INS and image-based methods shows the advantages of a potential combination of both approaches. The integration of the laser triangulation sensor into the set-up of the UWV confirms the potential of the combination of echo sounder and triangulation measurements. An exemplary multi temporal river survey approves the capability of the UWV for deformation analyses. Further, an improved laser triangulation sensor with a multi-line laser diode may enable more extensive underwater measurements.:Contents 1 Introduction 1 1.1 Objectives of this Thesis 1 1.2 Outline of this Thesis 1 2 Development of the Uncrewed Water Vehicle 3 2.1 Development 3 2.2 Sensor Configuration 4 2.2.1 INS and GNSS 4 2.2.2 Panorama Camera 4 2.2.3 RGB Camera 5 2.2.4 Mobile Lidar 5 2.2.5 Echo sounder 5 2.2.6 Underwater Laser Triangulation 5 2.3 System architecture 5 Sardemann et al., 2018: Acquisition of geometrical Data of small Rivers with an Unmanned Water Vehicle 7 Abstract 9 1. Introduction 9 2. The Unmanned Water Vehicle 9 2.1 Components 9 2.2 Time Synchronization 9 2.3 Calibration 10 3. Data Acquisition 10 4. Data Processing and Results 11 4.1 Lidar 11 4.2 Echo Soundings 12 4.3 Fusion with UAV data 12 5. Summary and Outlook 12 Acknowledgements 12 References 12 Sardemann et al., 2023: Camera-aided orientation of mobile lidar point clouds acquired from an uncrewed water vehicle 15 Abstract 17 1 Introduction 17 1.1 Uncrewed Water Vehicles as Multisensor Platforms 17 1.2 Camera based Orientation 18 1.3 Outline and Innovations of this Article 19 2 Platform Orientation Determination 19 3 Calibration of Lidar to Camera Orientation 20 3.1 Geometric Calibration 20 3.2 Time Synchronization 22 4 Lidar Point Transformation 22 5 Experiments 23 5.1 Reference Point Cloud 24 5.2 Calibration and Synchronization results 24 5.3 Transformation of mobile lidar point clouds 25 6 Accuracy Analysis 27 6.1 Theoretical Accuracy 27 6.2 Experimental Results 29 7 Conclusions 31 References 32 Sardemann et al., 2021: Strict geometric calibration of an underwater laser triangulation system 35 Abstract 37 1 State of the art 37 2 Method 37 2.1 Set-Up 37 2.2 Line Detection 38 2.3 Depth Determination 38 2.4 Calibration 38 2.5 Measurement Volume 39 3 Experiments and Results 39 3.1 Calibration 39 3.2 Measurements 40 4 Summary and Outlook 40 Acknowledgements 40 References 40 Sardemann et al., 2022: Accuracy Analysis of an Oblique Underwater Laser Lightsheet Triangulation System 41 Abstract 43 Zusammenfassung 43 1 Introduction 44 2 Background and State of the Art 44 3 System Design 46 4 Measurement Method 47 4.1 Line Measurement 47 4.2 Determination of 3D coordinates 48 4.3 Calibration 49 5 Measurement Volume 50 6 Statistical Accuracy Analysis 50 6.1 Influence of image measurement 51 6.2 Influence of Camera IOR 51 6.3 Influence of Camera EOR 51 6.4 Influence of Laser EOR 51 6.5 Influence of Refractive Index 51 6.6 Summarized Estimation of Accuracies 51 7 Experiments and de Facto Achieved Accuracies 52 7.1 Reference Objects 52 7.2 Single Profile Scan 52 7.3 Scanning Mode 53 8 Summary and Outlook 54 9 Declaration 54 References 54 3 Syntheses 59 3.1 Comparison of INS- and Camera-based Orientation 59 3.1.1 Boresight alignment and lever-arm calibration 59 3.1.2 Theoretical error estimation 60 3.1.3 De facto achieved accuracies 60 3.1.4 Comparison of both approaches 61 3.2 Integrating the underwater laser triangulation sensor 62 4 Ongoing and Future Work 64 4.1 Deformation Analysis 64 4.2 Multiline Underwater Laser Triangulation 65 4.2.1 Calibration 66 5 Conclusion 69 6 Literature 71 List of Figures 77 List of Tables 81 List of Abbreviations 83Bedingt durch den Klimawandel treten seit einigen Jahren vermehrt extreme Wetterereignisse auf. Deren Auswirkungen, wie Sturzfluten, verursachen große Schäden an Landschaften und Infrastruktur und gefährden Menschenleben. Um Sturzfluten besser modellieren zu können, ist die Überwachung von Flüssen und fluvialen Prozessen erforderlich. Neben der Messung von Wasserständen und Fließgeschwindigkeiten an Pegeln, muss die Morphologie des Flusses so genau wie möglich bekannt sein. Bei der hydrodynamischen Hochwassermodellierung werden beispielsweise hochaufgelöste Flussmodelle für eine Vorhersage der überfluteten Gebiete benötigt. Durch den Vergleich des Flussprofils vor und nach einem Hochwasserereignis können Rückschlüsse auf Veränderungen in der Landschaft gezogen werden. Für umfassende Flussvermessungen müssen sowohl die Ufer oberhalb als auch die Flusssohle unterhalb der Wasseroberfläche erfasst werden. In dieser Dissertation wird die Konzeptionierung und Umsetzung eines photogrammetrischen Multisensorsystems auf einem unbemannten Wasserfahrzeug (uncrewed water vehicle – UWV) vorgestellt. Die Arbeit zeigt, dass ein UWV ein nützliches Messsystem zur Erfassung der Topographie von Flüssen ober- und unterhalb des Wasserspiegels ist und somit die Erfassung der Morphologie des Flusses ermöglicht. Um präzise 3D-Informationen der Ufer zu erhalten, werden eine Kamera und ein mobiler Laserscanner an der Plattform angebracht. Für die Vermessung des Flussprofils wird zunächst ein Einzelpunkt-Echolot eingesetzt. Die einzelnen Sensoren zeichnen ihre Daten in unterschiedlichen Koordinatensystemen auf. Für ein kombiniertes Modell des Flusses müssen diese Messungen in einem gemeinsamen Koordinatensystem fusioniert werden. Daher wird eine Kalibriermethode vorgestellt, die die Bestimmung der relativen Orientierungen zwischen den Sensoren ermöglicht. Laserscanner-Messungen liefern detaillierte Informationen über die Uferbereiche. Da der Sensor auf einer beweglichen Plattform eingesetzt wird, ist die Georeferenzierung der 3D-Punkte von großer Bedeutung. Dafür müssen Position und Orientierung des Scanners während der gesamten Erfassung bekannt sein. Dies wird üblicherweise mit einem inertialen Navigationssystem (INS) gelöst, das aus einer IMU (Inertial Measurement Unit) und einem GNSS-Empfänger (Global Navigation Satellite System) besteht. Aufgrund von Abschattungen durch die Ufervegetation und Mehrwegeeffekten an der Wasseroberfläche ist die Satellitenortung auf Flüssen jedoch oft fehleranfällig. Darüber hinaus werden IMUs durch elektrische Felder auf der kleinen Plattform beeinflusst, was zu Drifts bei der Orientierungsbestimmung führt. Daher wird eine unabhängige Methode zur Bestimmung der Position und Orientierung der Plattform vorgestellt. Dazu werden die Bilder der auf dem UWV angebrachten Kamera verwendet. Deren Orientierung wird mit photogrammetrischen Mehrbildverfahren bestimmt. Basierend auf einer relativen Orientierung zwischen Kamera- und Scanner-Koordinatensystem werden diese Orientierungen zur Georeferenzierung der Laserscannerpunkte verwendet. Die entwickelte Kalibriermethode ermöglicht eine schnelle und hochgenaue Bestimmung der relativen Orientierung Das Echolot liefert aufgrund des Messprinzips in flachen Gewässern üblicherweise keine exakten Daten. Mittels eines Lasertriangulationssensors können auch in diesen Bereichen Gewässertiefen gemessen werden, weshalb eine Kombination beider Verfahren aufgrund ihrer gegensätzlichen Eigenschaften sinnvoll ist. Die Lasertriangulation ermöglicht hochgenaue linienhafte Abtastungen im Nahbereich und ist eine etablierte Methode in der optischen Industrievermessung. Um das Verfahren für Unterwassermessungen nutzen zu können, muss das Sensorsystem, bestehend aus einer Kamera und einem Linienlaser, zunächst in einem wasserdichten Glasgehäuse untergebracht werden. Das von der Laserdiode emittierte Licht wird dann an den Grenzflächen von Luft zu Glas und von Glas zu Wasser mehrfach gebrochen. Es wird eine Methode zur exakten Modellierung und Kalibrierung dieser Strahlengänge vorgestellt. Außerdem wird das theoretische Genauigkeitspotenzial evaluiert. In praktischen Versuchen, die zunächst im Labor durchgeführt wurden, konnte die zuvor abgeschätzte Submillimeter-Genauigkeit des Systems bestätigt werden. Die Ergebnisse der vorgestellten Methoden bieten Ansätze für Weiterentwicklungen. Ein Vergleich von INS- und bildbasierten Verfahren zeigt die Vorteile der potenziellen Kombination beider Ansätze. Die Integration des Lasertriangulationssensors in den Messaufbau des UWV zeigt das Potential der Kombination von Echolot- und Triangulationsmessungen. Eine beispielhaft durchgeführte multitemporale Flussvermessung bestätigt die Leistungsfähigkeit des UWV für Deformationsanalysen. Darüber hinaus könnte ein verbesserter Lasertriangulationssensor mit einer Mehrlinien-Laserdiode flächenhafte Unterwassermessungen ermöglichen.:Contents 1 Introduction 1 1.1 Objectives of this Thesis 1 1.2 Outline of this Thesis 1 2 Development of the Uncrewed Water Vehicle 3 2.1 Development 3 2.2 Sensor Configuration 4 2.2.1 INS and GNSS 4 2.2.2 Panorama Camera 4 2.2.3 RGB Camera 5 2.2.4 Mobile Lidar 5 2.2.5 Echo sounder 5 2.2.6 Underwater Laser Triangulation 5 2.3 System architecture 5 Sardemann et al., 2018: Acquisition of geometrical Data of small Rivers with an Unmanned Water Vehicle 7 Abstract 9 1. Introduction 9 2. The Unmanned Water Vehicle 9 2.1 Components 9 2.2 Time Synchronization 9 2.3 Calibration 10 3. Data Acquisition 10 4. Data Processing and Results 11 4.1 Lidar 11 4.2 Echo Soundings 12 4.3 Fusion with UAV data 12 5. Summary and Outlook 12 Acknowledgements 12 References 12 Sardemann et al., 2023: Camera-aided orientation of mobile lidar point clouds acquired from an uncrewed water vehicle 15 Abstract 17 1 Introduction 17 1.1 Uncrewed Water Vehicles as Multisensor Platforms 17 1.2 Camera based Orientation 18 1.3 Outline and Innovations of this Article 19 2 Platform Orientation Determination 19 3 Calibration of Lidar to Camera Orientation 20 3.1 Geometric Calibration 20 3.2 Time Synchronization 22 4 Lidar Point Transformation 22 5 Experiments 23 5.1 Reference Point Cloud 24 5.2 Calibration and Synchronization results 24 5.3 Transformation of mobile lidar point clouds 25 6 Accuracy Analysis 27 6.1 Theoretical Accuracy 27 6.2 Experimental Results 29 7 Conclusions 31 References 32 Sardemann et al., 2021: Strict geometric calibration of an underwater laser triangulation system 35 Abstract 37 1 State of the art 37 2 Method 37 2.1 Set-Up 37 2.2 Line Detection 38 2.3 Depth Determination 38 2.4 Calibration 38 2.5 Measurement Volume 39 3 Experiments and Results 39 3.1 Calibration 39 3.2 Measurements 40 4 Summary and Outlook 40 Acknowledgements 40 References 40 Sardemann et al., 2022: Accuracy Analysis of an Oblique Underwater Laser Lightsheet Triangulation System 41 Abstract 43 Zusammenfassung 43 1 Introduction 44 2 Background and State of the Art 44 3 System Design 46 4 Measurement Method 47 4.1 Line Measurement 47 4.2 Determination of 3D coordinates 48 4.3 Calibration 49 5 Measurement Volume 50 6 Statistical Accuracy Analysis 50 6.1 Influence of image measurement 51 6.2 Influence of Camera IOR 51 6.3 Influence of Camera EOR 51 6.4 Influence of Laser EOR 51 6.5 Influence of Refractive Index 51 6.6 Summarized Estimation of Accuracies 51 7 Experiments and de Facto Achieved Accuracies 52 7.1 Reference Objects 52 7.2 Single Profile Scan 52 7.3 Scanning Mode 53 8 Summary and Outlook 54 9 Declaration 54 References 54 3 Syntheses 59 3.1 Comparison of INS- and Camera-based Orientation 59 3.1.1 Boresight alignment and lever-arm calibration 59 3.1.2 Theoretical error estimation 60 3.1.3 De facto achieved accuracies 60 3.1.4 Comparison of both approaches 61 3.2 Integrating the underwater laser triangulation sensor 62 4 Ongoing and Future Work 64 4.1 Deformation Analysis 64 4.2 Multiline Underwater Laser Triangulation 65 4.2.1 Calibration 66 5 Conclusion 69 6 Literature 71 List of Figures 77 List of Tables 81 List of Abbreviations 8

THE USE OF MARINE RADAR FOR INTERTIDAL AREA SURVEY AND MONITORING COASTAL MORPHOLOGICAL CHANGE

Surveying and monitoring the dynamic morphology of intertidal areas is a logistically challenging and expensive task, due to their large area and complications associated with access. This thesis describes a contribution to the nearshore survey industry; an innovative methodology is developed and subsequently applied to marine radar image data in order to map topography within the intertidal area. This new method of intertidal topographical mapping has a reasonable spatial resolution (5 m) and operates over a large radial range (~4 km) with the required temporal resolution to observe both event-based and long-term morphological change (currently bi-weekly surveys). This study uses nearly three years of radar image data collected during 2006-2009 from an installation on Hilbre Island at the mouth of the Dee estuary, northwest UK. The development of the novel 'radar waterline method' builds on previous waterline techniques and improves upon them by moving the analysis from the spatial to the temporal domain, making the analysis extremely robust and more resilient to poor quality image data. Results from radar topographical surveys are compared to those of a LiDAR survey during October 2006. The differences compare favourably across large areas of the intertidal zone, within the first kilometre 97% of radar-derived elevations lie within 1 m of LiDAR estimations. Concentrations of poor estimations are seen in areas that are shown to be shadowed from the radar antenna or suffering from pooling water during the ebb tide. The full three-year dataset is used to analyse changing intertidal morphology over that time period using radar-derived surveys generated every two weeks. These surveys are used to perform an analysis of changing sediment volume and mean elevation, giving an indication of beach 'health' and revealing a seasonal trend of erosion and accretion at several sites across the Dee estuary. The ability of the developed technique to resolve morphological changes resulting from storm events is demonstrated and a quantification of that impact is provided. The application of the technique to long-range (7.5 km) marine radar data is demonstrated in an attempt to test the spatial and operational limitations of this new method. The development of a mobile radar survey platform, the Rapidar allows remote areas to be surveyed and provides a platform for potential integration with other survey instruments. A description of the potential application to coastal management and monitoring is presented. Areas of further work intended to improve vertical elevation accuracy and robustness are proposed. This contribution provides a useful tool for coastal scientists, engineers and decision-makers interested in the management of coastal areas that will form part of integrated coastal management and monitoring operations. This method presents several key advantages over traditional survey techniques including; the large area of operation and temporal resolution of repeat surveys, it is limited primarily by topographical shadowing and low wind conditions limiting data collection

Elastic LADAR modeling for synthetic imaging applications

The Digital Imaging and Remote Sensing Image Generation (DIRSIG) model was developed to create synthetic images of remotely sensed scenes (Schott et al. 1999). It is a quantitative model based on first principles that calculates the radiance reaching the sensor from the visible region of the spectrum through to the long-wave. DIRSIG generates a very accurate representation of what a sensor would see by modeling all processes involved in the imaging chain. Currently, DIRSIG only models light from passive sources such as the sun, blackbody radiation due to the temperature of an object, and local incoherent illuminants. Active systems allow the user to tailor the illumination source for specific applications. Remote sensing Laser Detection and Ranging (LADAR) systems that use a laser as the active source have existed for almost 40 years (Fiocco and Smullin 1963). LADAR systems are used to locate the position of an object. Light Detection and Ranging (LIDAR) systems are used to derive the properties of an object, such as density or chemical composition. Recently, advances in tunable lasers and infrared detectors have allowed much more sophisticated and accurate work to be done, but a comprehensive spectral LADAR/LIDAR modelhas yet to be developed. To provide a tool to assist in LADAR/LIDAR development, this research incorporates a first-principle-based elastic LADAR/LIDAR model into DIRSIG. It calculates the spectral irradiance at the focal plane for both the atmospheric and topographic return, based on the system characteristics and the assumed atmosphere. The model accounts for the geometrical form factor, a measure of the overlap between the sensor and receiver field of view, in both the monostatic and bistatic cases. The model includes the effect of multiple bounces from topographical targets. Currently, only direct detection systems are modeled. Several sources of noise are extensively modeled, such as speckle from rough surfaces and atmospheric turbulence phase effects

Entwicklung von Full-Waveform Stackingverfahren zur Detektion schwacher Gewässerbodenechos in der Laserbathymetrie

Airborne Laserbathymetrie stellt eine effiziente und flächenhafte Messmethode für die Erfassung der sich ständig im Wandel befindlichen Gewässersohlen von Inlandgewässern und küstennahen Flachwasserbereichen dar. Bei diesem Verfahren wird ein kurzer grüner Laserpuls ausgesandt, welcher mit allen Objekten entlang des Laserpulspfades interagiert (z.B. Wasseroberfläche und Gewässerboden). Die zum Sensor zurückgestreuten Laserpulsanteile (Echos) werden in einem zeitlich hochaufgelösten Messsignal (Full-Waveform) digitalisiert und gespeichert. Allerdings ist das Messverfahren aufgrund von Gewässertrübung in seiner Eindringtiefe in den Wasserkörper limitiert. Die Gewässerbodenechos werden bei zunehmender Gewässertiefe schwächer, bis sie nicht mehr zuverlässig detektierbar sind. Diese Arbeit zeigt, wie mit neuartigen Methoden schwache Gewässerbodenechos in Full-Waveforms detektiert werden können, welche durch die Standardauswerteverfahren nicht mehr berücksichtigt werden. Im Kernstück der Arbeit werden zwei Verfahren vorgestellt, die auf einer gemeinsamen Auswertung dicht benachbarter Messdaten basieren. Unter der Annahme eines stetigen Gewässerbodens mit geringer bis moderater Geländeneigung führt die Zusammenfassung mehrerer Full-Waveforms zu einer Verbesserung des Signal/Rausch-Verhältnisses und einer Verstärkung von schwachen Gewässerbodenechos, welche folglich zuverlässiger detektiert werden können. Die Ergebnisse zeigen eine erhebliche Erhöhung der auswertbaren Gewässertiefe (bis zu +30 %), wodurch eine deutlich größere Fläche des Gewässerbodens abgedeckt werden konnte (Flächenzuwachs von bis zu +113 %). In umfassenden Analysen der Ergebnisse konnte nachgewiesen werden, dass die hinzugewonnenen Gewässerbodenpunkte eine gute Repräsentation des Gewässerbodens darstellen. Somit leisten die in dieser Arbeit entwickelten Verfahren einen wertvollen Beitrag zur Steigerung der eingangs beschriebenen Effizienz der Airborne Laserbathymetrie.:Kurzfassung Abstract 1 Einleitung 1.1 Motivation 1.2 Ziele der Dissertation 1.3 Aufbau der Arbeit 2 Einführung in bathymetrische Messverfahren 2.1 Hydrographie und Bathymetrie 2.2 Airborne LiDAR Bathymetrie 2.2.1 Grundlagen Airborne Laserscanning 2.2.2 Der Pfad des Laserpulses 2.2.3 Fehlereinflüsse 2.3 Die Full-Waveform 2.3.1 Aufbau und Merkmale einer Full-Waveform 2.3.2 Systemwaveform 2.3.3 Full-Waveform Auswerteverfahren 2.4 Hydroakustische Messverfahren 2.4.1 Messprinzip 2.4.2 Echolot Varianten 2.4.3 Fehlereinflüsse 3 Nichtlineare Full-Waveform Stacking-Verfahren zur Detektion und Extraktion von Gewässerbodenpunkten – Beitrag 1, Beitrag 2, Beitrag 3 3.1 Signalbasiertes nichtlineares Full-Waveform Stacking 3.2 Volumetrisches nichtlineares Ortho-Full-Waveform Stacking 4 Anwendung von nichtlinearen Full-Waveform Stacking-Methoden auf maritime Gewässer – Beitrag 4 4.1 Studiengebiet in der Nordsee 4.2 Datengrundlage 4.3 Erste Ergebnisse einer Pilotstudie in küstennahen Bereichen der Nordsee 4.4 Untersuchungsgebiet 4.5 Klassifikation der Wasseroberflächenpunkte 4.6 Visualisierung der Ergebnisse 4.7 Genauigkeit und Zuverlässigkeit 4.8 Mehrwert der Verfahren 5 Potential der Full-Waveform Stacking-Methoden zur Ableitung der Gewässertrübung – Beitrag 5 6 Diskussion und weiterführende Arbeiten 6.1 Geometrische Modellierung der Laserpulsausbreitung 6.2 Einfluss der Gewässereigenschaften auf die Gewässerbodenbestimmung 6.3 Unterschätzung der Wasseroberfläche 6.4 Nutzung von Gewässertrübungsinformation für die Beurteilung der Zuverlässigkeit der Gewässertiefenbestimmung 6.5 Auswirkung der Nachbarschaftsdefinition beim signalbasiertem Full-Waveform Stacking 6.6 Gegenüberstellung signalbasiertes und volumetrisches Full-Waveform Stacking 6.7 Erweiterung des Full-Waveform Stackings mit dem Multi-Layer-Ansatz 7 Fazit der Dissertation 7.1 Zusammenfassung 7.2 Einordnung der Dissertation 7.3 Mehrwert der Dissertation Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Symbolverzeichnis AbkürzungsverzeichnisAirborne laser bathymetry is an efficient and area-wide measurement method for the detection of the permanently changing water bottoms of inland waters and shallow water areas close to the coast. In this method, a short green laser pulse is emitted, which interacts with all objects along the laser pulse path (e.g. water surface and bottom). The backscattered laser pulse components (echoes) are digitized and stored in a high temporal resolution measurement signal (full-waveform). However, the measurement method is limited in its penetration depth into the water body due to water turbidity. The water bottom echoes become weaker as the water depth increases until they are no longer reliably detectable. This work shows how novel methods can be used to detect weak water bottom echoes in full-waveforms that are no longer accounted for by standard processing methods. In the core of the work, two methods are presented which are based on a joint evaluation of closely adjacent measurement data. Under the assumption of a steady water bottom with low to moderate slope, the combination of several full-waveforms leads to an improvement of the signal-to-noise ratio and an enhancement of weak water bottom echoes, which consequently can be detected more reliably. The results show a significant increase in the analyzable water depth (up to +30 %), allowing a much larger area of the water bottom to be covered (increase up to +113 %). Comprehensive analyses of the results proved that the added water bottom points are a good representation of the water bottom. Thus, the methods developed in this work constitute a valuable contribution to increase the efficiency of airborne laser bathymetry described at the beginning.:Kurzfassung Abstract 1 Einleitung 1.1 Motivation 1.2 Ziele der Dissertation 1.3 Aufbau der Arbeit 2 Einführung in bathymetrische Messverfahren 2.1 Hydrographie und Bathymetrie 2.2 Airborne LiDAR Bathymetrie 2.2.1 Grundlagen Airborne Laserscanning 2.2.2 Der Pfad des Laserpulses 2.2.3 Fehlereinflüsse 2.3 Die Full-Waveform 2.3.1 Aufbau und Merkmale einer Full-Waveform 2.3.2 Systemwaveform 2.3.3 Full-Waveform Auswerteverfahren 2.4 Hydroakustische Messverfahren 2.4.1 Messprinzip 2.4.2 Echolot Varianten 2.4.3 Fehlereinflüsse 3 Nichtlineare Full-Waveform Stacking-Verfahren zur Detektion und Extraktion von Gewässerbodenpunkten – Beitrag 1, Beitrag 2, Beitrag 3 3.1 Signalbasiertes nichtlineares Full-Waveform Stacking 3.2 Volumetrisches nichtlineares Ortho-Full-Waveform Stacking 4 Anwendung von nichtlinearen Full-Waveform Stacking-Methoden auf maritime Gewässer – Beitrag 4 4.1 Studiengebiet in der Nordsee 4.2 Datengrundlage 4.3 Erste Ergebnisse einer Pilotstudie in küstennahen Bereichen der Nordsee 4.4 Untersuchungsgebiet 4.5 Klassifikation der Wasseroberflächenpunkte 4.6 Visualisierung der Ergebnisse 4.7 Genauigkeit und Zuverlässigkeit 4.8 Mehrwert der Verfahren 5 Potential der Full-Waveform Stacking-Methoden zur Ableitung der Gewässertrübung – Beitrag 5 6 Diskussion und weiterführende Arbeiten 6.1 Geometrische Modellierung der Laserpulsausbreitung 6.2 Einfluss der Gewässereigenschaften auf die Gewässerbodenbestimmung 6.3 Unterschätzung der Wasseroberfläche 6.4 Nutzung von Gewässertrübungsinformation für die Beurteilung der Zuverlässigkeit der Gewässertiefenbestimmung 6.5 Auswirkung der Nachbarschaftsdefinition beim signalbasiertem Full-Waveform Stacking 6.6 Gegenüberstellung signalbasiertes und volumetrisches Full-Waveform Stacking 6.7 Erweiterung des Full-Waveform Stackings mit dem Multi-Layer-Ansatz 7 Fazit der Dissertation 7.1 Zusammenfassung 7.2 Einordnung der Dissertation 7.3 Mehrwert der Dissertation Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Symbolverzeichnis Abkürzungsverzeichni

Ocean remote sensing techniques and applications: a review (Part II)

As discussed in the first part of this review paper, Remote Sensing (RS) systems are great tools to study various oceanographic parameters. Part I of this study described different passive and active RS systems and six applications of RS in ocean studies, including Ocean Surface Wind (OSW), Ocean Surface Current (OSC), Ocean Wave Height (OWH), Sea Level (SL), Ocean Tide (OT), and Ship Detection (SD). In Part II, the remaining nine important applications of RS systems for ocean environments, including Iceberg, Sea Ice (SI), Sea Surface temperature (SST), Ocean Surface Salinity (OSS), Ocean Color (OC), Ocean Chlorophyll (OCh), Ocean Oil Spill (OOS), Underwater Ocean, and Fishery are comprehensively reviewed and discussed. For each application, the applicable RS systems, their advantages and disadvantages, various RS and Machine Learning (ML) techniques, and several case studies are discussed.Peer ReviewedPostprint (published version

Overview of field operations during a 2013 research expedition to the southern Beaufort Sea on the RV Araon

Research experiments conducted and preliminary findings The Expedition ARA04C is a multidisciplinary research program in the Beaufort Sea, carried out in collaboration between the Korea Polar Research Institute (KOPRI), Geological Survey of Canada (GSC), Department of Fisheries and Ocean (DFO), Monterey Bay Aquarium Research Institute (MBARI), and the Alfred Wegener Institute (AWI). The Expedition ARA04C on the IBRV Araon took place from September 6 to September 24, 2013 (Figure 0.1). Multiple research experiments were undertaken to study geological processes related to degrading permafrost, fluid flow and degassing, and associated geohazards, paleo-oceanography of the Beaufort shelf and slope region, as well as physical and chemical oceanography measurement of the Arctic Ocean linked with continuous atmospheric studies. The expedition focused on two main research areas: offshore Barrow, Alaska, from September 7 to September 9, 2013, and the Canadian Beaufort Sea from September 10 to September 24, 2013. Multichannel seismic data, in conjunction with an ocean-bottom-seismometer (OBS) study were collected to support drilling proposals especially IODP pre-proposal #806 (Dallimore et al., 2012), and to verify distribution and internal structures of the offshore permafrost occurrences (Figure 0.2). The multi-channel seismic data were acquired on the outer continental shelf of the Canadian Beaufort Sea, totaling 14 lines with ~435 line-kilometers and ~4,500 shot gathers (Chapter 3). The combined multichannel seismic and OBS data will be processed post-expedition at KOPRI and the GSC, and will allow detailed velocity analyses to investigate the permafrost signature and help mapping zones of high-velocity sediments indicative of the presence of ice (Chapter 4). Individual shot gathers collected during the multichannel seismic program show clear refraction arrivals with velocities around 2000m/s in areas of expected permafrost occurrence, and shot gathers lacked such arrivals in zones where the permafrost was predicted to be absent. It is therefore expected that the OBS data, once processed, will also show clear refracted arrivals for velocity analyses. Continuous sub-bottom profiler (SBP) and multibeam data were collected along all ship tracks for detailed subsurface imaging of sediment structures and permafrost, as well as for core-site location verification (Chapter 5 and 6). During Expedition ARA04C, more than 3000 line-kilometers of SBP data were collected, co-located with multibeam and backscatter data. These data are an essential part of the study of sub-seafloor permafrost distribution and provide insights into sediment dynamics at critical boundaries, such as the shelf edge. Along the shelf edge, the occurrence of pingo-like features (PLFs) result in a rugged landscape with thousands of PLFs piercing through the otherwise laminated sediments. More than 30 crossings of this critical shelf-edge boundary were made during this expedition, which complement data acquired in 2012 with the Huntec system and 3.5 kHz data provided by ArcticNet as part of the regional multibeam map of the study area. High resolution data provided critical new insights in deep-water fluid expulsion zones. Key new data were acquired over the area of the "Gary Knolls", where PLF structures occur at the shelf edge in water depth of only 50 to 60 m. All SBP data from this expedition will be post-processed and analyzed for the presence of sub-seafloor permafrost, occurrence of the PLF structures and indications for fluid and gas migration. Multibeam and backscatter data were collected along all ship tracks, adding to the database of existing information gathered through previous expeditions to the study region. Heat flow measurements were undertaken at eight stations (Figure 0.3) to study the thermal structure of fluid expulsion features, as well as degrading permafrost along a slope-shelf transect in the eastern Mackenzie Trough (Chapter 7). The data provide critical constraints on the distribution of sub-seafloor permafrost as well as the gas hydrate stability zone around fluid expulsion features. A very important finding is the observation made at the mud volcano in 420 m water depth, where seafloor temperatures are the highest in all observed stations, indicating active mud volcanism. Geological sampling using gravity coring and multi-coring tools was performed at strategic sites to support two research objectives. The first objective was to provide key data towards ongoing international research linked to IODP pre-proposals #753 (O'Regan et al., 2010) and #806 (Dallimore et al., 2012). The second objective was to collect core to define key seismo-stratigraphic horizons critical to the understanding of geohazards in the region (Chapter 8). In total, 21 gravity cores and 12 multi-cores were taken (Figure 0.4, Table 8.3). All cores were scanned with a multi-sensor core-logger to measure physical properties (Chapter 9). Most sediment analyses on the cores will be performed post-expedition at KOPRI, GSC, and laboratories of other University-based collaborators in Canada and Germany. Onboard, sub-samples were taken from all shallow multi-cores and selected gravity cores. On selected cores from the Canadian Beaufort study region pore-waters were extracted using rhizones. These samples will be analyzed postexpedition at MBARI. Water sampling and Conductivity-Temperature-Depth (CTD) profiling was undertaken at most core sites to study physical and chemical properties of the seawater (Figure 0.5). These station-measurements were complemented by continuous waterproperty and atmospheric measurements when the Araon was underway. Most samples taken will be analyzed post-expedition at KOPRI for DIC/TA, nutrients, DOC, and POC. The pH of seawater, underway data of pCO2, CH4, and N2O, as well as a variety of subsequent calculations is required for accurate estimates in the above listed parameters. Methane was also measured with a methane sensor attached to the CTD tool and at the mud volcano in 420 m water depth, methane concentrations of more than 100-times ocean background were seen. The methane plume was also acoustically imaged with the echo sounder systems on board the IBRV Araon. Further details on the water sampling and atmospheric measurements are given in Chapter 10 and 11

Comparison between the employ of a multibeam echosounder on an unmanned surface vehicle and the traditional photo-grammetric as techniques for documentation and monitoring of shallow-water cultural heritage sites: A case of study in the Bay of Algeciras

Over the last few years, due to various climatic, anthropogenic, and environmental factors, a large amount of submerged heritage has been unearthed and exposed to deterioration processes in the Bay of Algeciras. These impacts can be more severe in shallow waters, where the cultural heritage is more vulnerable to natural and human-induced impacts. This makes it urgent to document cultural heritage at risk of disappearing using different techniques whose efficiencies in the archaeological record need to be determined and compared. For this purpose, we have documented a shipwreck in the Bay of Algeciras using two techniques: photogrammetry and a multibeam echosounder. The photogrammetric method consists of obtaining a 3D model from numerous photographs taken of an object or a site. The processing software creates three-dimensional points from two-dimensional points found in the photographs that are equivalent to each other. Multibeam echosounders are capable of providing side scan imagery information in addition to generating contour maps and 3D perspectives of the surveyed area and can be installed in an unmanned surface vehicle. As a result, we have obtained two 3D visualisations of the shipwreck, i.e., digital copies, that are being used both for the analysis of its naval architecture and for its dissemination. Through the comparison of the two techniques, we have concluded that while a multibeam echosounder provides a detailed digital terrain model of the seabed, photogrammetry performed by divers gives the highest resolution data on objects and structures. In conclusion, our results demonstrate the benefits of this combined approach for accurately documenting and monitoring shipwrecks in shallow waters, providing valuable information for conservation and management efforts.This research was funded by: (1) Ministry of Science and Innovation, Spain, through the project “Vulnerability of littoral cultural heritage to environmental agents: impact of climate change (VOLICHE)” (PID2020-117812RB-I00/AEI /10.13039/501100011033): (2) European Regional Development Fund (FEDER), EU, Interreg V-A Spain-Portugal program (POCTEP) 2014–2020, through the project “KTTSeaDrones” (0622-KTTSEADRONES-5-E). (3) 2014–2020 ERDF Operational Programme and the Department of Economy, Knowledge, Business and University of the Regional Government of Andalusia, Spain, through the project “Between the Pillars of Hercules, underwater archaeology of a privileged space. The Bay of Algeciras (HERAKLES)”. (FEDER-UCA18-107327