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문제 정의
- Special thanks also 흥。to the residents of Ulleung Island for providing us with valuable infonnation, which greatly assisted us in delimiting the survey area. This paper is written as part of our contribution to the Millennium 2000 and EEZ Project.
제안 방법
- An EM-1002 multi-beam echo sounder was used to map the seafloor topography in the survey area. The CM800 side-scan sonar was not operated during this survey, to avoid interference from the side-scan sonar, which operates at the same 102 kHz frequency as the EM-1002 echo sounder.
- The sea-floor topography and the direction of ocean currents were also taken into consideration in choosing the survey areas. Subsequently, a comprehensive, integrated, marine geophysical survey of the sea-floor was carried out using the following methods: multi-beam echo sounder, marine magnetometer, and side-scan sonar. When the ship was located, it was photographed from a remotely operated vehicle (ROV), guided by the submarine Pathfinder, for the verification of the ship's identity.
- For a period of five years from 1999 to 2003, we performed comprehensive, integrated geophysical surveys to find the Russian cruiser Dmitri Donskoi that was scuttled during the Russo-Japanese War about 100 years ago. The main purpose of this survey was to identify the exact location of the ship, and to appraise the treasures contained therein with a view of recovering them.
- However, we adopted a technique to help in identifying the hull location from the magnetic anomaly already identified. The method involved inspecting the side-scan sonar or sea-floor topographic images at the locations of each of the 38 identified magnetic anomalies. By doing this, we hoped to obtain a clear image of the ship location.
- As the exact location of the sinking of the Dmitri Donskoi was not known, the first step was to analyse historical records of the Russo-Japanese maritime war. The methodology employed at this stage involved review of the existing historical wartime record data, and interviews of residents of the area. This was necessary to delimit the most Hkely areas, where the survey would be carried out.
- The next step used to identify the ship from the numerous data that we have was to carry out a comprehensive comparative analysis of the suspected strange anomalous objects. We illustrate this section with data for anomaly C shown in block 3 (Figure 11) which we suspected to be the most promising prospect identified from the comparative analysis.
- We used a combination of multi-beam echo sounder, marine magnetometer, and side-scan sonar to map precisely and to image the sea floor off Ulleung Island. The survey was carried out over a sloping sea-floor gorge area with the aim of locating the Dmitri Donskoi, a warship that was scuttled in the area 100 years ago. In general, magnetic surveys are expected to be very useful in locating steel artefacts, but are limited in identifying sunken vessels among volcanic rocks which have strong intrinsic magnetisation, such as are found in the survey area.
- Locations of identified strange magnetic objects were marked. These objects were re-verified through cross-checking with the magnetic profiles obtained from the survey.
- However, the severely uneven topography in the survey area prevented sonar returns being received in every case, and this also made it difficult to discern the ship. To overcome these problems, we found it necessary to conduct a comprehensive interpretation by comparing all of the geophysical images of the suspected anomaly with the sea-floor image. The multi-beam echo sounder produced an improved sea-floor image, even in the steeply sloping sea-floor environment, by using a narrower-angle beam.
- This seafloor image survey revealed 16 anomalous zones (Figure 9). We subsequently returned to these zones and carried out what we called a target survey, resulting in high-resolution seafloor images.
- Subsequently, a comprehensive, integrated, marine geophysical survey of the sea-floor was carried out using the following methods: multi-beam echo sounder, marine magnetometer, and side-scan sonar. When the ship was located, it was photographed from a remotely operated vehicle (ROV), guided by the submarine Pathfinder, for the verification of the ship's identity.
대상 데이터
- The survey area was chosen based on the information obtained from historical war records. It is located about 2 km away from Port Jeodong, Ulleung Island, in the East Sea of Korea, between longitudes 130°54' E and 130°58' E, and latitudes 37°28' N and 37°32' N (Figure 1). The water depth in the area varies from 100 m to 2000 m.
- (A) Magnetic anomaly (nT), (B) side-scan sonar image, and (C) multi-beam image at site C in Figure 10. The artefact was identified as the Dmitri Donskoi.
- The multi-beam echo sounder confirmed the depth at the location where the ship was found to be precisely 400 m (Fig 11C). The location is about 2 km away Port Jeodong, Ulleung Island. The site is a sea-floor valley with steep slopes of approximately 50°.
- This was achieved by minimizing the effects from non-reflection by narrowing down the beam angle, and by reducing the speed of the vessel used for data acquisition. The ship located in the survey was found to contain naval guns, and was later verified as the warship Dmitri Donskoi. The ship was identified by comparing the actual shape found with information obtained from historical records from the Russo-Japanese War.
- The location is about 2 km away Port Jeodong, Ulleung Island. The site is a sea-floor valley with steep slopes of approximately 50°;. The vicinity of the ship is surrounded by volcanic rocks (Figure 12).
- By doing this, we planned to retrieve 200% image coverage of the sea floor. The vessel was navigated along parallel northeastern- southwestern lines direction during data acquisition. Forty-nine lines, approximately perpendicular to the valley direction, were surveyed (Figure 3).
후속연구
- The steel upper part of the ship is well preserved, although some parts have started to decay. Further thorough investigation is necessary for a closer examination and sal.,age of the Dmitri Donskoi.
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