Seabed Characterization through Image Processing of Side Scan Sonar Case Study: Bontang and Batam

Acoustic waves propagate through a medium meet the Snell’s Law, its energy is reflected and some are scattered back at certain angle. The Side Scan Sonar (SSS) methods use this principle to identify seabed character. The intensity of the backscatter greatly depends on the morphology and sediments texture or rocks distributed on seabed.The intensity of backscatter waves is a representation of the morphology, sediments texture, and types of rock that distributed on the seabed, therefore it is possible to estimate sedimentary texture and identify the presence of rocks or coral reefs based on this information. In this publication authors estimate sediments texture, rocks or coral reefs based on backscatter intensity through the image processing on the Side Scan Sonar (SSS) image. Intensity will be converted into pixel values on the image with range value 1-255 (gray scale image) and entropy values which are statistical measures of randomness. Entropy value is maximum when most of pixel value image is in the middle of the colour spectrum range (between very dark to very bright), in contrast, it is minimum when pixel value is in the spectrum of very dark or very bright. Based on both parameters, classification is conducted. The classification is carried out on the SSS image at Bontang and Batam that have very different seabed characters.The classification results using an image processing shows that the distribution of sediment textures consist of 4 (four) classes for either Batam or Bontang. In the Bontang area, very fine sediments were identified which are associated with low value of both intensity and entropy - dark zones in gray scale images, and coarse sediments associated with high value of both intensity and entropy - bright zone in the gray scale image. Similar characteristic is observed in Batam area, which are identified fine sediment (associated to low intensity) - coarse sediments (high intensity). In contrast to Bontang, in Batam the entropy exhibit the opposite value, high value are correlated to fine sediment and vice versa. This might be due to the presence of rocks and sedimentary structures.Keywords: Side Scan Sonar, Intensity, Backscatter and entropy.Gelombang akustik sebagian besar energinya dipantulkan memenuhi prinsip snellius dan sebagian kecil dihamburkan balik dengan sudut. Metode Side Scan Sonar (SSS) memanfaatkan prinsip hambur-balik gelombang untuk mengidentifikasi permukaan dasar laut. Intensitas gelombang dari karakter hambur-balik akan sangat tergantung morfologi dan tekstur sedimen atau batuan dari permukaan dasar lautnya. Intensitas gelombang hambur-balik merupakan representasi dari morfologi, tekstur sedimen, dan jenis batuan yang tersebar di permukaan dasar laut, sehingga sangat memungkinkan untuk melakukan estimasi tekstur sedimen dan identifikasi keberadaan batuan maupun terumbu karang berdasarkan informasi tersebut. Pada publikasi ini akan dilakukan estimasi tekstur sedimen atau batuan berdasarkan intensitas hambur-balik melalui image yang dihasilkan oleh Metode Side Scan Sonar (SSS). Intensitas akan dikonversi ke dalam nilai pixel dalam image dengan rentang nilai 1-255 (gray scale image) dan nilai entropi yang merupakan ukuran statistik ketidakteraturan dari image. Entropi akan maksimum ketika nilai pixel kebanyakan di tengah dari rentang spektrum warna dan sebaliknya akan minimum ketika nilai pixelnya berada di spektrum warna sangat gelap atau sangat terang. Berdasarkan kedua parameter tersebut, kemudian dilakukan klasifikasi. Klasifikasi dilakukan pada data SSS Bontang dan Batam yang memiliki karakter permukaan dasar laut yang sangat berbeda.Hasil klasifikasi dengan image processing memperlihatkan pola sebaran tekstur sedimen masing-masing terdiri dari 4 (empat) kelas baik untuk Batam atau Bontang. Pada area Bontang teridentifikasi sedimen sangat halus yang berasosiasi dengan intensitas dan entropy rendah - zona gelap pada gray scale image dan sedimen kasar yang berasosiasi dengan intensitas dan entropy tinggi - zona terang pada gray scale image. Karakter yang sama juga teramati pada area Batam, yaitu teridentifikasi sedimen halus (berasosiasi dengan intensitas rendah) - sedimen kasar (intensitas tinggi). Namun, berbeda dengan di Bontang, di Batam nilai entropi menunjukkan nilai yang sebaliknya, yaitu nilai tinggi berkorelasi dengan sedimen halus, dan sebaliknya. Hal ini diperkirakan akibat keberadaan batuan dan struktur sedimen.Kata Kunci: Side Scan Sonar, Intensitas, Hambur balik dan Entropi

High-resolution underwater robotic vision-based mapping and three-dimensional reconstruction for archaeology

Documenting underwater archaeological sites is an extremely challenging problem. Sites covering large areas are particularly daunting for traditional techniques. In this paper, we present a novel approach to this problem using both an autonomous underwater vehicle (AUV) and a diver-controlled stereo imaging platform to document the submerged Bronze Age city at Pavlopetri, Greece. The result is a three-dimensional (3D) reconstruction covering 26,600 m2 at a resolution of 2 mm/pixel, the largest-scale underwater optical 3D map, at such a resolution, in the world to date. We discuss the advances necessary to achieve this result, including i) an approach to color correct large numbers of images at varying altitudes and over varying bottom types; ii) a large-scale bundle adjustment framework that is capable of handling upward of 400,000 stereo images; and iii) a novel approach to the registration and rapid documentation of an underwater excavations area that can quickly produce maps of site change. We present visual and quantitative comparisons to the authors' previous underwater mapping approaches

3D Recording and Interpretation for Maritime Archaeology

This open access peer-reviewed volume was inspired by the UNESCO UNITWIN Network for Underwater Archaeology International Workshop held at Flinders University, Adelaide, Australia in November 2016. Content is based on, but not limited to, the work presented at the workshop which was dedicated to 3D recording and interpretation for maritime archaeology. The volume consists of contributions from leading international experts as well as up-and-coming early career researchers from around the globe. The content of the book includes recording and analysis of maritime archaeology through emerging technologies, including both practical and theoretical contributions. Topics include photogrammetric recording, laser scanning, marine geophysical 3D survey techniques, virtual reality, 3D modelling and reconstruction, data integration and Geographic Information Systems. The principal incentive for this publication is the ongoing rapid shift in the methodologies of maritime archaeology within recent years and a marked increase in the use of 3D and digital approaches. This convergence of digital technologies such as underwater photography and photogrammetry, 3D sonar, 3D virtual reality, and 3D printing has highlighted a pressing need for these new methodologies to be considered together, both in terms of defining the state-of-the-art and for consideration of future directions. As a scholarly publication, the audience for the book includes students and researchers, as well as professionals working in various aspects of archaeology, heritage management, education, museums, and public policy. It will be of special interest to those working in the field of coastal cultural resource management and underwater archaeology but will also be of broader interest to anyone interested in archaeology and to those in other disciplines who are now engaging with 3D recording and visualization

Adaptable underwater networks: The relation between autonomy and communications

This paper discusses requirements for autonomy and communications in maritime environments through two use cases which are sourced from military scenarios: Mine Counter Measures (MCM) and Anti-Submarine Warfare (ASW). To address these requirements, this work proposes a service-oriented architecture that breaks the typical boundaries between the autonomy and the communications stacks. An initial version of the architecture has been implemented and its deployment during a field trial done in January 2019 is reported. The paper discusses the achieved results in terms of system flexibility and ability to address the MCM and ASW requirements

The spatial and temporal distribution of pipe and pockmark formation

This research concentrates on two study areas.  A family of blowout pipes from North Namibia imaged in 3D seismic data; and a group of large buried pockmarks and a field of small seabed pockmarks from the Western Nile Deep Sea Fan (NDSF) imaged in ultra high resolution 2D data.  The general themes of this research are pipe and pockmark morphology and formation process, their spatial and temporal distribution and the magnitude and frequency of fluid flux through the conduit. A family of blowout pipes from Namibia exhibit a variety of seismic characteristics, with the largest pipes containing a blowout crater and evidence of possible stacked palaeo-pockmarks. Pipe formation is shown to be intermittent and persistent throughout the Neogene. The spatial position of pipes adheres to both basinal and local controls. A group of large buried pockmarks on the NDSF are interpreted to have formed between 15,000 yrs BP and 125,000 yrs BP, the majority of which are believed to have formed at the same time c. 60,000-80,000 yrs BP.  These buried pockmarks show evidence for highly focused, episodic fluid flow following burial of the pockmark.  The longevity of post formation fluid migration is estimated to be ~50,000-100,000 yrs. A field of > 13,800 small seabed pockmarks (Nile Deep Sea Fan) are interpreted to have formed within the last 1,000 yrs.  Spatial statistics identified an exclusion zone or drainage cell surrounding each pockmark which is not penetrated by the formation of any other pockmark.  A conceptual model for a drainage cell is proposed whereby pockmark formation dissipates, a radius/area of fluid and overpressure, thereby preventing the formation of another pockmark within that cell

Signal Processing for Synthetic Aperture Sonar Image Enhancement

This thesis contains a description of SAS processing algorithms, offering improvements in Fourier-based reconstruction, motion-compensation, and autofocus. Fourier-based image reconstruction is reviewed and improvements shown as the result of improved system modelling. A number of new algorithms based on the wavenumber algorithm for correcting second order effects are proposed. In addition, a new framework for describing multiple-receiver reconstruction in terms of the bistatic geometry is presented and is a useful aid to understanding. Motion-compensation techniques for allowing Fourier-based reconstruction in widebeam geometries suffering large-motion errors are discussed. A motion-compensation algorithm exploiting multiple receiver geometries is suggested and shown to provide substantial improvement in image quality. New motion compensation techniques for yaw correction using the wavenumber algorithm are discussed. A common framework for describing phase estimation is presented and techniques from a number of fields are reviewed within this framework. In addition a new proof is provided outlining the relationship between eigenvector-based autofocus phase estimation kernels and the phase-closure techniques used astronomical imaging. Micronavigation techniques are reviewed and extensions to the shear average single-receiver micronavigation technique result in a 3 - 4 fold performance improvement when operating on high-contrast images. The stripmap phase gradient autofocus (SPGA) algorithm is developed and extends spotlight SAR PGA to the wide-beam, wide-band stripmap geometries common in SAS imaging. SPGA supersedes traditional PGA-based stripmap autofocus algorithms such as mPGA and PCA - the relationships between SPGA and these algorithms is discussed. SPGA's operation is verified on simulated and field-collected data where it provides significant image improvement. SPGA with phase-curvature based estimation is shown and found to perform poorly compared with phase-gradient techniques. The operation of SPGA on data collected from Sydney Harbour is shown with SPGA able to improve resolution to near the diffraction-limit. Additional analysis of practical stripmap autofocus operation in presence of undersampling and space-invariant blurring is presented with significant comment regarding the difficulties inherent in autofocusing field-collected data. Field-collected data from trials in Sydney Harbour is presented along with associated autofocus results from a number of algorithms

Quantifying submarine channel morphology and kinematics on structurally complex slopes: examples from the Niger Delta

Submarine channels form pronounced morphological features on the seafloor and play an important role in shaping the stratigraphic record. Over the last two decades, their morphology and architectural evolution have been studied in detail using a range of modern and ancient examples. While structural deformation is recognised as a major control, the temporal and spatial complexity associated with these systems means aspects of submarine channel dynamics and how their geomorphic expression translates into time-integrated sedimentary architecture, remain poorly understood. For example, structurally driven changes in slope morphology may locally enhance or diminish a channel’s ability to incise, aggrade and migrate laterally. In this thesis, I explore the sensitivity of submarine channel morphology to structural deformation and evaluate how channel-structure interactions are recorded in seismic stratigraphic architecture. I use novel seismic attribute analysis alongside concepts from landscape dynamics to provide quantitative insights into how the growth of structure on the southern Niger Delta slope has influenced submarine channel morphology and time-integrated stratigraphic architecture. From a 3D, time-migrated seismic reflection volume, I quantify a range of morphometric parameters including, channel gradient, width, depth, sinuosity, curvature, and stratigraphic mobility, on a number of modern and ancient submarine channel systems as they interact with structure. My results show that submarine channel morphology and longitudinal profile are unambiguously linked to the underlying structural template. The modern seafloor expression of submarine channels can be up to an order of magnitude higher aspect ratio and markedly more variable than their ancient, stratigraphic counterpart. Their depositional architectures are composite stratigraphic features that record the morphological response to spatial and temporal variations in structural growth rate. Based on this, three end-member styles of submarine channel architecture are recognised on structured slopes: pre-channel structural bathymetry, coeval positive relief, and coeval negative relief. This thesis quantifies how submarine channel systems integrate kinematic processes at the scale of the fundamental architectural unit, a channel element, and documents the systematic change in channel element kinematics on structured segments of the slope. My observations demonstrate the sensitivity of submarine channels to structural deformation and help us to constrain some of the most important sediment transport systems on planet Earth.Open Acces

Of His Bones are Coral Made: Submerged Cultural Resources, Site Formation Processes, and Multiple Scales of Interpretation in Coastal Ghana

Integrating theoretical and methodological approaches to formation processes across a range of scales from micro-artifact to region and from historical to environmental processes, this work explores the archaeology of the event related to submerged archaeological sites within the Elmina seascape of coastal Ghana. Building on and intersecting with the work of other scholars, this research is a unique approach to the investigation of submerged cultural remains related to historical maritime trade. Remote sensing surveys in 2009 led to the identification of three sites related to maritime trade, adding significantly to the two previously known sites, which include a circa 1650 shipwreck, referred to as the Elmina Wreck, and the remains of an early 18th century vessel in the Benya Lagoon. Drawing on remote sensing survey data, diver investigations, and the micro-sampling sediment coring technique developed over the course of field research, the historical and physical environment of coastal Elmina is studied as a means of interpreting the unique events surrounding a specific shipwreck, and to relate formation processes across the region to this and other sites. While archaeological evidence is limited, the complex study of formation processes, including the historical contexts of trade and the physical environmental has provided insights into events and practices of trade, destruction and preservation of submerged sites, and has provided a foundation for continued holistic investigation and maritime archaeological studies in the region. The methodological and theoretical approaches to formation processes form a model applicable to maritime research across the globe