Academic literature on the topic 'Bathymetry'

Thesis (M.S. in Physics) Naval Postgraduate School, Dec. 1996.<br>Thesis advisors, Richard Christopher Olsen, Newell Garfield. AD-A329 389. Includes bibliographical references (p. 73-75). Also available online.

Knowledge of water depth is a crucial for planning military amphibious operations. Bathymetry from remote sensing with multispectral or hyperspectral imagery provides an opportunity to acquire water depth data faster than traditional hydrographic survey methods without the need to deploy a hydrographic survey vessel. It also provides a means of collecting bathymetric data covertly. This research explores two techniques for deriving bathymetry and assesses them for use by those involved in providing support to military operations. To support this aim a fieldwork campaign was undertaken in May, 2000, in northern Queensland. The fieldwork collected various inherent and apparent water optical properties and was concurrent with airborne hyperspectral imagery collection, space-based multispectral imagery collection and a hydrographic survey. The water optical properties were used to characterise the water and to understand how they affect deriving bathymetry from imagery. The hydrographic data was used to assess the performance of the bathymetric techniques. Two methods for deriving bathymetry were trialled. One uses a ratio of subsurface irradiance reflectance at two wavelengths and then tunes the result with known water depths. The other inverts the radiative transfer equation utilising the optical properties of the water to derive water depth. Both techniques derived water depth down to approximately six to seven metres. At that point the Cowley Beach waters became optically deep. Sensitivity analysis of the inversion method found that it was most sensitive to errors in vertical attenuation Kd and to errors in transforming the imagery into subsurface irradiance reflectance, R(0-) units. Both techniques require a priori knowledge to derive depth and a more sophisticated approach would be required to determine water depth without prior knowledge of the area of interest. This research demonstrates that water depth can be accurately mapped with optical techniques in less than ideal optical conditions. It also demonstrates that the collection of inherent and apparent optical properties is important for validating remotely sensed imagery.

Thesis (M.S. in Physical Oceanography)--Naval Postgraduate School, June 2003.<br>Thesis advisor(s): Thomas H.C. Herbers, Edward B. Thornton. Includes bibliographical references (p. 37). Also available online.

This study proposes and demonstrates a through-water photogrammetry approach for Satellite Derived Bathymetry (SDB), which may be used to map nearshore bathymetry in the Canadian Arctic. A four step process is used: First, a standard photogrammetric extraction is performed on 2 m resolution WorldView stereo imagery, then apparent depths are calculated by referencing submerged points to the extracted elevation of the water level seen in the image. Due to the effects of refraction, these apparent depths are underestimates, and a refraction correction factor is applied to convert to actual depths. Finally, tidal stage at the time of image acquisition is used to bring depths to chart datum. A post processing step may be applied to remove erroneous depths caused by water surface objects such as boats, debris, or large waves. This was demonstrated in six study areas across Nunavut, Canada to test its robustness under a variety of environmental conditions, including different seafloor types, and under varying sea states. The six study sites were (with vertical accuracy given in Root Mean Square Error/and vertical bias, both in meters): eastern Coral Harbour (1.18/0.03), western Coral Harbour (0.78/-0.32), Cambridge Bay (1.16/0.08), Queen Maud Gulf (0.97/0.13), Arviat (1.02/0.13), and Frobisher Bay, where bathymetry extraction largely failed due to unfavourable sea surface conditions. These findings show that the proposed method has similar or better vertical accuracy as currently established SDB approaches; however, it has several benefits over the established methods which make it better suited for the Arctic. Namely, not requiring the precise atmospheric correction necessary for physics-based models, which is difficult at high latitudes; as well as being able to function in heterogeneous seafloor environments and not needing in-situ calibration data like the empirical spectral ratio approach, better suiting it to remote Arctic waters which often lack existing bathymetric survey data.

The definition of the shape of the geoid is a fundamental objective of geodesy, since it allows for the conversion between orthometric and ellipsoidal height systems. The geoid can be computed from gravity values measured over the surface of the earth, and considerable effort continues to achieve a global coverage of gravity values. One technique that has been very successful in recent years in providing gravity coverage in areas which previously have been too difficult to access is airborne gravimetry. This technique has proved very useful in covering near offshore regions, for example. The coastal regions of Australia are recognised as locations where airborne gravimetry has the potential to fill in missing gravity data. A pilot survey using an airborne gravity meter was undertaken off the north east coast of Australia. In areas that remain unsurveyed it is sometimes useful to fill in the missing gravity data values with predicted gravity values. Previous research has examined the possibility of predicting gravity values from other observed quantities. The best success has been achieved by using the gravity effect calculated from bathymetric information. Often the corresponding isostatic compensation is computed, and the combined bathymetric-isostatic gravity effect is used. However, the type and extent of compensation that exists in any particular region mostly remains unknown. Theoretical considerations indicate that the short wavelength part of the gravity field may be adequately modelled by the gravity effect of the bathymetry alone, without reference to an assumed compensation mechanism. With this in mind, a prediction scheme has been developed which utilises the short wavelength gravity field information implied by the bathymetry, combined with the long wavelength gravity field information from existing observed gravity. This scheme allows the prediction of ???fill-in??? gravity values in areas with limited observed gravity. The prediction technique was used on a test set of data off the east coast of Greenland. The prediction technique was seen to outperform a simple interpolation of gravity values by approximately ten percent. Geoid computations performed with the predicted gravity values indicate that the prediction technique can provide significant improvements in computed geoids.

Surface elevation is likely the most fundamental property of our planet. In contrast to land topography, bathymetry, its underwater equivalent, remains uncertain in many parts of the World ocean. Bathymetry is relevant for a wide range of research topics and for a variety of societal needs. Examples, where knowing the exact water depth or the morphology of the seafloor is vital include marine geology, physical oceanography, the propagation of tsunamis and documenting marine habitats. Decisions made at administrative level based on bathymetric data include safety of maritime navigation, spatial planning along the coast, environmental protection and the exploration of the marine resources. This thesis covers different aspects of ocean mapping from the collection of echo sounding data to the application of Digital Bathymetric Models (DBMs) in Quaternary marine geology and physical oceanography. Methods related to DBM compilation are developed, namely a flexible handling and storage solution for heterogeneous sounding data and a method for the interpolation of such data onto a regular lattice. The use of bathymetric data is analyzed in detail for the Baltic Sea. With the wide range of applications found, the needs of the users are varying. However, most applications would benefit from better depth data than what is presently available. Based on glaciogenic landforms found in the Arctic Ocean seafloor morphology, a possible scenario for Quaternary Arctic Ocean glaciation is developed. Our findings suggest large ice shelves around parts of the Arctic Ocean during Marine Isotope Stage 6, 130–200 ka. Steered by bathymetry, deep water from the Amerasian Basin of the Arctic Ocean flows over the central Lomonosov Ridge into the Eurasian Basin. This water mass is traced on its continuing way towards Greenland and the Fram Strait. At the Morris Jesup Rise, bathymetry plays an important role in the partial re-circulation of the water into the Amerasian Basin.<br><p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Submitted.</p>

South Africa has an extensive coastline offshore of which lies the prominent South African continental shelf, a relatively flat extension of the onshore coastal plain. The continental shelf is host to major mineral and petroleum deposits, home to South Africa’s major sea fisheries and full of navigation hazards. Therefore, knowledge of the seafloor features, or bathymetry, of the continental shelf is essential to understanding both its long-term geological evolution and present-day use for resources and navigation. Unfortunately there has been little advancement in our knowledge of the South African continental shelf since the marine studies of the 1970’s and 1980’s which culminated in the “Bathymetry around Southern Africa” map of Dingle et al. (1987). Although bathymetric mapping equipment and techniques have greatly improved during the last few decades, very little high resolution bathymetric data of the South African continental margin are currently available for scientific use, with the majority of the high resolution multi-beam echo-sounding bathymetric surveys being undertaken by privately owned mineral exploration and mining companies (such as De Beers, Alexkor, Petro SA, Petroleum Agency of South Africa, etc.), the Council for Geoscience and the South African Navy and Hydrographic Office. More recent advances in satellite altimetry have had a major impact on ocean floor bathymetric mapping especially in deep ocean areas where the sea surface generally reflects the underlying bathymetry. The Department of Agriculture, Forestry and Fisheries (DAFF) annually collect single-beam echo-sounding data in order to monitor the abundance of fish species along the South African continental shelf and along with that collect seafloor bathymetry as an additional benefit. The aim of this project is to create a detailed bathymetric map of the continental shelf of South Africa by using digital single-beam echo-sounding data collected by the Fisheries Division of the DAFF over the last two decades. The bathymetric dataset of ±7 million single-beam echo-sounding data points was manually processed, gridded and exported to produce a detailed bathymetric map of the entire South African continental shelf between the Orange River mouth and Kosi Bay complemented by Satellite Altimetry data from the ETOPO 1 – 1 Arc-Minute Global Relief Model (Amante and Eakins 2009) for the deep ocean area adjacent to the continental shelf. The single- beam bathymetric data were collected by the F.R.S. Africana II and F.R.S. Algoa vessels using SIMRAD EKS-38, EK 400, EK 500 and more recently the EK 60 single-beam echo-sounders along with a the SIMRAD ES38B split beam transducer. The West Coast and South Coast margins have the greatest bathymetric detail due to DAFF’s Cape Town base of operations, whilst the East Coast margin is less detailed due to fewer research campaigns in this area. The Bathymetric Map of the South African Continental Margin produced in this thesis reveals several new and more detailed bathymetric features. New bathymetric features include the northern extension of the Olifants Valley submarine canyon, details of the rocky inner shelf related to glacial period sea level lowstands, as well as the coast parallel wave cut terraces and palaeo dune ridges on the middle shelf between Cape Seal and Cape Recife. Other prominent bathymetric features such as Childs Bank, Cape Canyon, Cape Point Valley, the offshore submerged river valleys of the Breede and Gouritz Rivers and the east-west trending, basement anticlinal ridges situated at the southernmost extent of the Agulhas Arch were revealed in greater detail by this study. The underlying geology, physical Oceanography, drainage patterns as well as eustatic sea-level fluctuations can all be linked to the bathymetry of the continental shelf, which is why this thesis examines the influences of each of these factors on the seafloor morphology around the South African coastline.

"August 2001." Includes bibliographical references (leaves 77-80). Examines the susceptibility of existing signal processing methods to errors and identifies other possible causes of depth error not accounted for by existing signal processing methods, by analysis of the detected laser return waveform data. Methods to improve depth accuracy are investigated.