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Overview of the old and new IHO Data Protection SchemesReport of Hydrographic and Oceanographic ResearchesIHO S-63“IHO Data Protection Scheme” is the standard for protecting S-57 ENCs from piracy and unauthorized use. It has been used worldwide. Part 15 of the IHO S-100“Universal Hydrographic Data Model” is the upgraded version of S-63 and will be used for S-100 products, not only for ENCs, in the near future. This article gives comparisons between them and offers some considerations.
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Presentation of parallels and meridians in the Maritime-domain-awareness (MDA) Situational Indication Linkages, UMISHIRUReport of Hydrographic and Oceanographic ResearchesThe Maritime-domain-awareness （MDA） Situational Indication Linkages, UMISHIRU, operated by the Japan Coast Guard, is a Web-GIS （Geographic Information System） featuring more than 200 items of marine information. Since being upgraded from the former Japan Marine Cadastre in 2019, UMISHIRU has covered global-scale information items, but it can overlay the parallels and meridians to a limited extent on the map. This paper describes a method for beginners to draw parallels and meridians beyond the limited range, and likewise to draw other geographic lines.
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Presentation of depth information in the Maritime-domain-awareness (MDA) Situational Indication Linkages, UMISHIRUReport of Hydrographic and Oceanographic ResearchesWhen thinking about general use in waters, depth information is one of the necessar y pieces of information. By using a Web-GIS system such as the Maritime-domain-awareness （MDA） situational indication linkages, UMISHIRU, this can be effectively achieved. Unfortunately, the UMISHIRU does not itself have the depth information in. In this paper, we describe how to compile the depth data of the J-EGG500 and ETOPO1 and present the depth information in the UMISHIRU for the beginning UMISHIRU user.
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Statistical data of sea ice observation in the recent 30 yearsReport of Hydrographic and Oceanographic ResearchesIce information center open every winter at the 1st Regional Coast Guard Headquarters. For safe navigation, we collect and analyze data of sea ice observations from C.G. offices, stations and relative organizations, and offer ice information as sea ice condition charts and navigational warnings. In this report, we summarize observation results of coastal sea ice stations from C.G. offices etc. in the recent 30 years.
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Trial of creating of tidal current grid data for the Akashi StraitReport of Hydrographic and Oceanographic ResearchesThe Japan Coast Guard Hydrographic and Oceanographic Department has provided data on tidal current, which is one of the ocean currents, as area information （tidal current grid data）. In recent years, technologies related to the ocean have advanced, and new information such as detailed water depth data has been acquired. In addition, the mainstream method of providing tidal current grid data is digital, which has a high variety of information usages from printed matter. The Hydrographic and Oceanographic Department is conducting research to create new tidal current grid data corresponding to these. Between 2019 and 2020, the Akashi Strait was examined as part of first trial at creating tidal current grid data.
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On the tidal current harmonic constants in Ise BayReport of Hydrographic and Oceanographic ResearchesThe tidal current harmonic constants in Ise Bay are owned by the Japan Coast Guard Hydrographic and Oceanographic Department and is a point-like one created by continuous day and night observation of tidal currents at fixed points. There is a grid-like one created in 2004 based on joint reserch with the Japan Hydrographic Association （2004, 2005a, 2005b）. This time, as part of the research to create tidal current grid data, tidal current harmonic constants were created from the current direction and current velocity data observed by the Ise Bay Ocean Short Wave Radar operated by the Nagoya Port and Airport Technical Research Office, Chubu Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism. We examined these tidal current harmonic constants.
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Optimized observation cycle for the tidal harmonic analysisReport of Hydrographic and Oceanographic ResearchesThe Japan Coast Guard observes the tidal time series using the Autonomous Ocean Vehicle （AOV） to precisely determine datum levels. As the AOVs utilize solar energy for their observation equipment, interruptions of observation caused by the power shortage due to decrease in the amount of sunshine in the winter becomes an operational issue. In this paper, we investigate whether short observations during interruptions or prolonged observation are effective to obtain reliable tidal harmonic constants. We found that short observations of more than 24 hours during interruptions or observations from the next year on the same date as the interruption make the tidal harmonic constants close to the value calculated from no missing data. The results of this study can be used as index for deciding the implementation of observation in winter or making plans for observation using AOVs.
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Installation of a seafloor geodetic observation system on the S/V KoyoReport of Hydrographic and Oceanographic ResearchesThe Hydrographic and Oceanographic Department, Japan Coast Guard （JHOD）, has installed an acoustic transducer on all of its survey vessels （excluding the S/V Tenyo） to conduct GNSS-Acoustic ranging （GNSS-A） observations. JHOD also installed a seafloor geodetic observation system on the new S/V Koyo（4,000 tons） commissioned in March 2021 to improve the efficiency of its GNSS-A observations. In this article, we report on the outline of the seafloor geodetic observation system installed on the S/V Koyo, the survey method and the resulting relative position between the GNSS antenna and the transducer, and the result of the test observation. The result of the test observation indicated that the horizontal components of the seafloor site position observed by the S/V Koyo agree with the trend of the time series estimated from our regular GNSS-A observations. On the other hand, the vertical component indicated the possibility of a positioning bias, which would necessitate further evaluation by continuing the GNSS-A observations using the S/V Koyo.
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Trial to visualize the distribution and seasonal variation of ALB-measurable areas estimated from remotely sensed diffused attenuation coefficient dataReport of Hydrographic and Oceanographic ResearchesEfficient Airborne Lidar Bathymetry （ALB） surveys involve elaborate prior adjustments and operation planning processes based on a consideration of various relevant conditions. We attempted to visualize the distribution and its seasonal variation of the ALB measurable areas around Japan using a remotely sensed dataset of diffused attenuation coefficients, which represents the optical characteristics of the seawater, to help reduce the burden of the operation planning. The results showed that the maximum measurable depth at a certain spot seasonally varies and, subsequently, the distribution of the measurable areas varies as well. The estimated maximum penetration depths have proved to make a useful index for operation planning, while its future verification is required.
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Developing the standard operating procedures of ellipsoidally referenced surveys at coastal waters in Japan: trials of bathymetric data processing and verification of their results†Report of Hydrographic and Oceanographic ResearchesIn recent years, with the spread and improvement in the accuracy of kinematic GNSS positioning, ellipsoidally referenced surveys （ERS） have become practically possible, which in principle do not require tide observations during the bathymetric surveys. In this paper, as the first step of a trial to establish the standard operating procedures for ERS in Japan, we presented the practical operating procedures of bathymetric data processing in ERS and vertical datum model estimation, by using the existing bathymetric data in Tokyo Bay. In this case, the validity of the ERS operating procedures was verified by comparing the depths in the ERS procedures with those in the conventional procedures with tidal reduction.
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On the calculation of the tide tableReport of Hydrographic and Oceanographic ResearchesThis article reviews the algorithms used for various calculations such as predicting the tidal heights and currents for the tide table, using the tide table, and obtaining tidal harmonic constants.
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Operation and observations of the Autonomous Ocean Vehicle (AOV.Report of Hydrographic and Oceanographic ResearchesJapan Coast Guard has been operating the Autonomous Ocean Vehicle （AOV） since 2016 in order to precisely determine datum levels and observe meteorological and oceanographic conditions. In this paper, we report the problems and improvements concerning long-term observation. Moreover, we review the tide level data processing method related to determining datum level precisely and show recent examples of meteorological and oceanographic observation.
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Installation of seafloor geodetic observation system on the S/V Heiyo.Report of Hydrographic and Oceanographic ResearchesThe Hydrographic and Oceanographic Department, Japan Coast Guard (JHOD) installed an acoustic transducer on the bottoms of the S/V Meiyo (550 tons) in March 2008, the S/V Takuyo (2,400 tons) in February 2010, the S/V Kaiyo (550 tons) in March 2012, and the S/V Shoyo (3,000 tons) in November 2012 and started sailing GNSS-Acoustic (GNSS-A) observations. The JHOD also installed a seafloor geodetic observation system on the New S/V Heiyo (4,000 tons) in January 2020 for more efficient and precise seafloor positioning. In this report, we discuss the outline of the seafloor crustal movement observation system installed in the S/V Heiyo, the position measurement method and the measurement results of the GNSS antenna and the transducer, and the results of the test observation
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Historical nautical charts published by the Japanese Navy during the Meiji era and owned by domestic and overseas libraries and museums.Report of Hydrographic and Oceanographic ResearchesWe surveyed the Japanese nautical charts published in the Meiji era in the collections of domestic and overseas libraries and museums in 2019. As a result, we found the following new facts.The Tokyo National Museum has in its holdings the charts exhibited at the first and third National Industrial Exhibitions held in 1877 and 1890. The Leiden University Libraries in Netherlands own two volumes of the Dai-Nippon Kaigan Jissokuzu, the atlas of Japanese nautical charts that the Japanese Hydrographic Office compiled based on its own hydrographic surveys in its founding period.While it is known that the Kyoto University Museum owns many charts that were published in the Meiji era and stamped with “Donated by the Navy”, some documents of the National Archives revealed that these charts were donated by the Japanese Imperial Navy in 1911, upon request from the Kyoto Imperial University.
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Coverage of a tide gauge for water level reduction.Report of Hydrographic and Oceanographic ResearchesIn this study, we proposed criterion for the “same” tidal variation as a means of determining the acceptable range of the water depth error based on the water level reduction. The proposed criterion is 9 cm of the standard deviation of the difference between the observed tidal levels and the tidal levels in the survey area. In order to investigate the geospatial coverage where the criterion is acceptable, the standard deviation of the tidal level difference from 2013 to 2017 using the tide gauge data from the Japan Oceanographic Data Center was calculated. In most areas along the coast of the Japan Sea from Susa to Wakkanai, the standard deviation of the difference of the tidal level between the two adjacent tide gauges is less than 9 cm. However, this does not apply to the Tsugaru Strait and the Pacific Ocean from Shibushi to Hanasaki or the area where the Kurosio gets closer to the coast, or when the difference of the astronomical tide is large. This criterion can be interpreted as being within the permissible range of the water depth required for the Special Order of hydrographic surveys. In these areas, data from the reliable permanent tide gauge nearest to the survey area, instead of a temporary tidal observation just in front of the survey area, should be used for water level reduction.
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The time of lower low water.Report of Hydrographic and Oceanographic ResearchesIn many waters around Japan, it is well known that, among the low tides that occur twice a day during the spring tide, the tide level is lower in the middle of the night in the winter and in the daytime in the summer. We pointed out the approximate time of the lower low tide and showed its spatial distribution in Japan using the tide prediction equation. It is shown that, on the Pacific coasts, the lower low tide of the spring tide appears in the winter nighttime and in the summer daytime, although on the Japan Sea coasts, the lower low tide of the spring tide appears in the winter daytime and in the summer nighttime. It is also shown that this tendency does not depend on the year.
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Impact of the Fukushima Daiichi Nuclear Power Station Accident on the Sea of Japan and the Sea of Okhotsk.Report of Hydrographic and Oceanographic ResearchesThe Japan Coast Guard has been investigating radioactivity in the waters around Japan since 1959. The 2011 Tohoku Earthquake that occurred off the Pacific coast caused a tsunami. The TEPCO Fukushima Daiichi Nuclear Power Station was severely damaged and a radioactive accident occurred. Radioactive materials were released into the environment, flowed out from the coastlines of Niigata and Yamagata prefectures to the ocean, and transferred to the Notsuke Strait by ocean currents. By utilizing the half-lives of 134Cs and 137Cs, 137Cs of seafloor sediment could be separated into the concentration due to the global fallout and the concentration due to three accidents at TEPCOʼs Fukushima Daiichi Nuclear Power Station. It was suggested that silt clay in the seafloor sediments selectively adsorb radioactive cesium.
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Oceanographic research by the Japan Coast Guard―An overview of the past ten years.Report of Hydrographic and Oceanographic ResearchesThis paper summarizes the results and related findings of the oceanographic observations conducted by the Hydrographic and Oceanographic Department, Japan Coast Guard, over the past 10 years. The Kuroshio took a large meander route after an interval of 12 years. The needs for observation equipment and results are gradually changing.
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Decadal progress and results of the GNSS-A seafloor geodetic observation from 2011 to 2020Report of Hydrographic and Oceanographic ResearchesThe Japan Coast Guard has been developing and operating seafloor geodetic observation with the GNSS‒ Acoustic ranging combined technique （GNSS-A） for more than 20 years. Important scientific results were provided by the GNSS-A obser vation. In this decade, GNSS-A obser vation has detected seafloor movements due to the co- and post-seismic crustal deformation of the 2011 off the Pacific coast of Tohoku Earthquake, and the interseismic seafloor velocity along the Japan Trench, the Sagami Trough, and the Nankai Trough, including their temporal variations. These results provided essential information on interplate earthquakes. Decadal improvements of the GNSS-A technique and efficiency have enhanced the observation frequency. Observation accuracy was also improved by introducing a new analysis method where the spatial gradient components of the sound speed structure are estimated and corrected. Recently, we embarked on an effort to develop an “open” GNSS-A for the further development of GNSS-A community.
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Observations of sea-area volcanoes by the Japan Coast Guard between 2012 and 2020 and the associated resultsReport of Hydrographic and Oceanographic ResearchesThe Japan Coast Guard has been observing volcanoes in the adjacent seas of Japan for safety ship navigation, volcanic disaster prevention, and securing marine interests. The target volcanoes are volcanic islands and submarine volcanoes in the Izu-Ogasawara Islands and the Ryukyu Islands, and the observations are being made using aircraft and survey vessels. Observations by aircraft are visual observations, thermal observations, and geomagnetic observations, and observations by survey vessels are topographical surveys, geomagnetic and gravity observations, water sampling, sediment dredging, and crustal structure exploration. In the last decade, large-scale eruptions have occurred on Nishinoshima Volcano and Kuchinoerabujima Volcano, and eruptive activity has continued intermittently on Suwanosejima Volcano, Sakurajima Volcano, and Satsuma-Iojima Volcano. In addition, unusual geothermal and hydrothermal phenomena were observed in Myojinsho and Aogashima. The Japan Coast Guard has endeavored to prevent volcanic disasters by appropriately observing these volcanic activities and reporting the results to The Coordinating Committee for Prediction of Volcanic Eruptions. In addition, a comprehensive survey of volcanoes is conducted in advance during calm normal times of volcanic activity for the purpose of comparison with the time of eruption. The observation of marine volcanoes has many challenges that are different from those of land volcanoes, but it is necessary to promote the sophistication of those observations while incorporating new technologies such as observations from satellites and quantitative analysis of the color tone of the discolored water.
