I present a method to produce graphical images for PCs (Personal Computers) with an 8-bit-color monitor. Several different images are shown using geographical and geophysical data of different scales. The types of images shown are categorized into three, i.e. (i) pseudo color image, (ii) gray-scale shaded relief and (iii) overlaid images of two different types of data. Most of the presented images are derivatives from the data which I named 'bit-synthesized image' in this study. The 'bit-synthesized image' is defined as an image which bears two different types of information in each picture element (pixel) in a specific fromat. Using the specially arranged CLUT (Color Look Up Table) which is determined by the 'bit-synthesized image, We can see the two different types of information on the same image displayed on the color monitor screen. Image processing methods (IPM) have more advantages over the use of contour map and wire-framed surface expressions of 2D data when the size of data set becomes large, e. g. larger than 100 × 100. Using IPM, reduction of the CPU time and memory space for large data sets and more flexible 3-dimensional viewing techniques are available.

View full abstract

A seawater hydraulic actuator system for a subsea robot has been developed. The system consists of a high pressure axial piston pump, flow control servo valves and actuators which transform controlled flow into motion, and it is very effective in miniaturizing a subsea robot. In order to confirm overall characteristics of this power system, a prototype tele-manipulator for underwater work has been also developed. A manipulator control system is based on a master-slave method with some telepresence technique to provide an easy operation of a manipulator. Through running experiments in underwater manipulation, overall characteristics of the seawater hydraulic system and working performance of the prototype subsea manipulator have been confirmed to be good enough for practical use.

View full abstract

An ocean broadband downhole seismometer (OBDS) was emplaced in Hole 794D in the northern Yamato Basin, the Japan Sea during ODP Leg 128 by D/V JOIDES Resolution. The seismometer capsule was clamped within basaltic rock section at 714.5 m below sea floor at a water depth of 2,807 m. The OBDS has a three-component feedback type accelerometer and the digital signals were telemetered via a logging cable to shipboard for real-time recording during the first phase of the experiment. Real-time recording allowed full recovery of six-channel data (two gains per component, 16-bit each) at 80Hz/ch sampling rate. A high resolution seismic reflection/refraction experiment was conducted during the real-time recording. The OBDS, nine ocean bottom seismometers (OBS's) which were deployed by R/ V Tansei-maru, and a single channel hydrophone streamer were used to obtain detailed local crustal structure from the controlled-source experiment. Airguns were used as a controlled source and were shot with two 9-liter or a single 17-liter chamber. Profiles consisted of two circles and two linear lines.
We determined the velocity structure near the linear profiles using records of the OBDS, four OBS's which were deployed every 25 km and a hydrophone streamer. First, one-dimensional structures under each OBS were derived by the tau-sum inversion. Second, two-dimensional structures were obtained by a forward 2-D ray tracing method. The sedimentary layer has a P-wave velocity of 1.7 km/s. An acoustic basement with a velocity of 4.5 km/s underlies the sedimentary layer. A layer with a velocity of 6.2 km/s exists under the 4.5 km/s layer. Though we could not determine the thickness of the crust in the study area, the depth of Moho must be more than 14 km from sea surface. The upper crustal structure which is neither typically oceanic nor continental is similar to that in the southern Yamato Basin.

View full abstract

What has so far made it difficult for us to precisely measure terrestrial gravity on a ship in real time, is the fact that it had not been easy for us appropriately to separate a gravitational shift due to an Etovös effect from an acceleration due to a heaving motion of a ship.
The Etovös effect is defined as a gravitational shift arising from a horizontal movement of a ship. Accordingly, if we want to measure gravity correctly on board, then we must properly compensate the errors resulting from the gravitational shift on the basis of the ground velocity of the ship.
By a method entitled above, Japan Hydrographic Department has recently succeeded in measuring a gravitational anomaly in real time efficiently and precisely, there by obtaining the correct gravity.
While the conventional methods, at first, detect and eliminate the errors one by one which are involved in the primary data on the gravity measured, the ground velocity of a ship, Etovos effect, and the depth of the sea, and then determine the gravitational anomaly, the proposed method determines the gravitational anomaly directly from those data, and after that, smooths the results thus determined to obtain the correct gravity.
Adoption of this method has significantly usable the results obtained from measurement of the gravity in the vicinity of a turning point of a ship, where the measurement has never been carry out. It has raised to nearly 100 percent, of the utilization of the primary data on the gravity thus measured.

View full abstract

The Philippine Sea plate is subducting beneath the NE Japan plate in the Sagami trough and the Nankai trough. The Izu peninsula, which has a thick crust, is located between the both troughs. the plate boundary of the Philippine Sea plate and the NE Japan plate is not distinct be cause of the existence of the Izu peninsula. That is why there are several hypotheses about the location of plate boundary between the Philippine Sea plate and the NE Japan plate.
Hydrographic Department, Maritime Safety Agency carried out multi-channel seismic reflection survey of the Sagami Bay. Several facts were revealed by the survey.
1) The extension of northern slope of Izu-Oshima island subducting beneath the Manazuru knoll which is located on the slope of the Izu peninsula.
2) The erosion is dominant in the axis of the Sagami trough.
3) A reverse fault is recognized on the shelf slope foot of the Izu peninsula to the east of Hatsushima island.
The reverse fault on the south of Manazuru knoll suggests that the bottom of the Sagami trough may be subducting beneath the Izu peninsula and that the plate boundary between the Philippine Sea plate and the NE Japan plate is located on the east of the Izu peninsula.

View full abstract

This system was developed for sensing of seabed condition with real-time observation at depth of up to 5,000 meters by employing high tensile optical fiber mechanical towing cable (OFM cable).
The system consists of the submarine vehicle which contains various precision sensors (CTD, water sampler etc) and two still-video cameras, the contorol and monitoring unit on board and the OFM cable.
In 1990-1991, the system was seted on a new "Hakuhou Maru" and it was able to be used at maximum depth of 5,500 meters successfully. We expext that this monitoring system will be widely used for some academic resercheres and for exploration of deepsea natural resouces.

View full abstract