Thales GeoSolutions (Pacific), Inc. San Diego, California, USA

Jerry.Wilson@thales-geosolutions.com

　

Testing, development and experience in meeting real-world survey requirements over the past year have resulted in a body of examples of improved multibeam backscatter data for seafloor mapping. These examples include fisheries habitat mapping, engineering site surveying, hydrographic charting, target detection, and deep ocean exploration programs across a wide geography and range of environments. Graphical illustrations of data results and interpretations from a selection of these operations will be presented.

　

The multibeam backscatter technology applied and the improvements that have been gained over the past year will be described. While most examples are from Reson systems, other systems will be included. Development of data acquisition and processing techniques are also illustrated and contrasted with side-scanning sonar data. Conclusions regarding survey planning and design are drawn as they vary importantly between the operational environment and the seafloor survey objectives.

　

　

Ocean Engineering Corp. Saitama, JAPAN

ocean-eng@pop17.odn.ne.jp

　

System 5400, side scan sonar with the function of interferometric swath bathymetry, has been studied for it's accuracy by a comparison with SeaBat9001, narrow multi-beam echo sounder, and PDR130D, single echo sounder, at the artificial undulated area.

　

The error between these results is focused to the difference of outfitting, positioning, sensors for adjustment and method of swath bathymetry. Comparison between swath bathymetry and scan image is also carried out with overlap of image and contours.

　

For the interferometric system with these studies, merit & demerit, limitation for use and future development will be discussed.

　

　

¹Institute of Computational Mathematics and Mathematical Geophysics Siberian Division, Russian Academy of Sciences, Novosibirsk, RUSSIA

mag@omzg.sscc.ru

　

²Institute of Volcanology, Far Eastern Division, Russian Academy of Sciences, Petropavlovsk-Kamchatsky, RUSSIA

　

At the first step precise bathymetric maps with the depth isolines and extreme points for the four areas, which cover the whole Kuril-Kamchatka region, were created. Information was taken from the depth sounding records and navigation maps. At the second stage, the scanned maps were semi-automatically digitized using a specially developed digitizing interface. At the final stage, the algorithm, developed by the authors, recalculates arbitrarily distributed depth values into a detailed gridded bathymetry. For the calculation at each grid point, where depth is to be found, the algorithm uses up to 9 points from a data source. They are chosen using two criteria: the first - the points must be located in various sectors (N, NE, E, SE, S, SW, W, NW) from a grid-point being calculated. And the second - they must be the nearest ones to this point in each sector. Then the spline interpolation is used for defining the depth value at the grid-point. Another algorithm uses a linear interpolation for obtaining depth value at the grid-point.

　

The new digital bathymetry on the rectangular grid with 1 arc minute resolution has been created for the numerical modeling. These data consist from four rectangular arrays of depth, which cover 200 km zone around the Kuril Islands and Kamchatka from 41.00°up to 61.00°Northern latitude. Using the proposed method and the same digitized data it is easy to create more detailed arrays of depth for this region.

　

　

¹Institute of Industrial Science, University of Tokyo Meguro-ku, Tokyo, JAPAN

moma@iis.u-tokyo.ac.jp

　

²Hydrographic Department, Japan Coast Guard Chuo-ku, Tokyo, JAPAN

　

Great earthquakes have occurred repeatedly in and around Japan islands. Many of them are categorized into interplate earthquakes that occur between the tip of the Eurasian continental plate and two subducting oceanic plates, that is, the Pacific and Philippine Sea plates. Some earthquakes have caused terrible disasters on human activities on the shore area of Japan. To understand the mechanism of such great interplate earthquake has been an urgent social request to be achieved as well as it has been an interesting earth science problem. Institute of Industrial Science and Hydrographic Department have been developing a method of seafloor geodesy that detects the deformation of the subsea crust for better understandings of the processes of the interplate earthquakes. A combination of kinematic GPS positioning and precise acoustic ranging technique is employed to achieve centimeter-level seafloor geodesy. First trial of this seafloor geodesy method at the Kumano trough, where the Philippine Sea plate subducts beneath Japan island arc, showed the system could locate the horizontal position of the seafloor reference point within 5 cm standard deviation of the acoustic ranging residuals.

　

The seafloor geodetic reference station network around Japan islands has been constructed after the initial observation. Eleven seafloor geodetic reference stations had been established on the subsea forearc crust of Japan island arc. Three more stations are planned to be added to the network in 2002. The observation that we visit the seafloor reference stations to make measurements two or three times a year has just been started.

　

　

¹National Institute of Advanced Industrial Science and Technology Tsukuba, JAPAN

m-yamamuro@aist.go.jp

　

²Ishigaki Tropical Station, Seikai National Fisheries Research Institute Fisheries Research Agency, Ishigaki, Okinawa, JAPAN

　

Seagrasses are flowering plants that have evolved to live in seawater. There are about 57 species of seagrass world wide, and 10 species are reported from subtropical coast in Japan. Seagrass beds are one of the most productive ecosystems, which supply a major food source for a number of aquatic grazing animals such as dugong and turtles.

　

Many problems face the long-term survival and health of seagrass population in world coastal zones. Anthropogenic pollutants have contributed most to seagrass declines around the world. Careless land development increased suspended sediments in run off, which also reduced light for seagrasses. Loss of seagrass habitats will mean loss of productivity in marine ecosystems as well as extinction of species that depends on seagrass for survival. Increase of such disturbance is expected in subtropical and tropical coast in Asia including Japan due to the economic development.

　

Seagrass boundaries have been mapped with conventional aerial photography. Remote sensing further tries to determine the species composition, which are, however, difficult to apply to the species that lived deep region down to depths of 10 meters. We developed the new mapping system of seagrass beds using ROV (Remote Observation Vehicle) equipped with the underwater digital camera. The position of ROV was determined by DGPS (Differential Global Positioning System) and LBL (Long Base Line System) based underwater acoustic navigation system. Automated differentiation between seagrasses and others in the digital pictures proved to be successful.