Storage-efficient method for generating contours focusing on roundness     

Hiroyuki Goto  Yoichi Shimakawa 《International journal of geographical information science》2016,30(2):200-220

A storage-efficient contour generation method, focusing on planar contours, is developed. Given cartographic elevations on a rectangular lattice, a continuous bivariate function, z = f(x, y), is determined by interpolating the elevation values. Then, we focus on a contour determined by z = constant. The contour curve is partitioned into multiple sections, each of which is exactly or approximately round. Three curvature types are introduced to evaluate the roundness of each section. The area and perimeter of the contour are computed by one-dimensional line integration using Green’s theorem. If the contour is open, it is divided into two curves starting from the same initial point, with the control points advancing in opposite directions. Two types of numerical experiments are performed to validate the effectiveness of the proposed method. One experiment uses an analytically defined elevation function and investigates the number of control points and computation time for a resulting computation error. The second experiment uses actual digital elevation model data of an isolated island in Japan and compares the proposed method with existing ones. Because the algorithm does not require lattice subdivision and the number of control points is drastically reduced, the proposed method is storage efficient.  相似文献   

A monitoring result of polychlorinated biphenyls (PCBs) in deep-sea organisms and sediments off Tohoku during 2012–2014: temporal variation and the relationship with the trophic position     

Naohiko Ohkouchi  H. Shibata  Y. Chikaraishi  H. Nomaki  N. O. Ogawa  T. Nagata  T. Goto  K. Fujikura  H. Kitazato 《Journal of Oceanography》2016,72(4):629-639

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The possibility of inferring paleoseismicity from paleomagnetic dating of speleothems, western Japan   总被引：2，自引：0，他引：2  

Hayao Morinaga  Takafumi Yonezawa  Yasuhisa Adachi  Hiroo Inokuchi  Hiroya Goto  Katsumi Yaskawa 《Tectonophysics》1994,230(3-4):241-248

Paleomagnetic dating of continuously growing stalagmites by comparing their paleomagnetic records with a standard record, has been applied to study the paleoseismic history of a region of western Japan. Three stalagmites (speleothems), which are assumed to have started growing since collapse of the limestone blocks on which they are formed, were collected from two limestone caves located below the Akiyoshi plateau, western Japan. From the paleomagnetic results, it is estimated that they began to grow at 6000, 2500 and 2000 yr B.P., respectively. On the assumption that their growth began immediately after their host limestone blocks fell, these three ages are interpreted to indicate the dates of past earthquakes in this region which triggered the break-off and fall of the blocks. Earthquakes are suggested because many huge collapsed limestone blocks and speleothems are observed in many caves in this region.  相似文献   

Resting cells of microorganisms in the 20–100 μm fraction of marine sediments in an Antarctic coastal area     

Mutsuo Ichinomiya  Miwa Nakamachi  Mitsuo Fukuchi  Akira Taniguchi 《Polar Science》2008,2(1):27-32

We investigated the morphological features, vertical sinking fluxes, and number densities of the resting cells of ice-associated microorganisms in the 20–100 μm fraction of natural marine sediments collected from ice-covered and ice-free areas around Syowa Station, Lützow-Holm Bay, East Antarctica. We identified the resting cells of various taxonomic groups, including the spores of a diatom, cysts of three dinoflagellates, cysts of five oligotrich ciliates, and the eggs of a mesozooplankton. This is the first report of oligotrich ciliate cysts from Antarctic waters. The resting spores of Thalassiosira australis (diatom), cysts of Polarella glacialis (dinoflagellate), and egg type 1 sink to the bottom sediment during summer. Our results suggest that some planktonic and ice-associated microorganisms in Antarctic coastal areas send their resting cells to the bottom sediments as seed populations for the following generation.  相似文献   

Variations in the thermal conductivities of surface sediments in the Nankai subduction zone off Tokai, central Japan     

Shusaku Goto  Tomonobu Mizoguchi  Ryo Kimura  Masataka Kinoshita  Makoto Yamano  Hideki Hamamoto 《Marine Geophysical Researches》2012,33(3):269-283

We investigated the relationship between variations in the thermal conductivity of surface sediments and the topography in the Nankai subduction zone off Tokai, central Japan, the easternmost part of the Nankai subduction zone, which has an accretionary prism with varied topography. We analyzed sediment thermal conductivity data obtained from the trough floor and accretionary prism. Variations in the thermal conductivity of sediments were related to the topographic features formed by accretionary prism development. Thermal conductivities of 1.1?W/m?K were measured on the trough floor where thick terrigenous turbidites have been deposited. The thermal conductivity of Nankai Trough floor sediments decreases from northeast to southwest along the trough, probably because of the decreased grain size and/or changes in sediment mineral composition. High thermal conductivities (??1.0?W/m?K) were measured in fault scarps on the accretionary prism. A landward increase in these values on the prism may be explained by decreased porosity of the sediments attributable to tectonic deformation during accretionary prism development. At the base of the fault scarp of the frontal thrust, low thermal conductivities (<0.9?W/m?K) were measured, likely reflecting the high porosity of the talus deposits. Low thermal conductivity (0.9?W/m?K) was also measured in slope basins on the accretionary prism, likely also related to the high porosity of the sediments. Our results demonstrate that, for accurate heat flow measurement in an area of varied topography, the geothermal gradient and the thermal conductivity of the sediments must be measured within regions with similar topographic features.  相似文献   

Numerical identification of tsunami boulders and estimation of local tsunami size at Ibaruma reef of Ishigaki Island,Japan          下载免费PDF全文

Masashi Watanabe  Kazuhisa Goto  Fumihiko Imamura  Chuki Hongo 《Island Arc》2016,25(5):316-332

Tsunami boulders deposited along the coast constitute important geological evidence for paleotsunami activity. However, boulders can also be deposited by large storm waves. Although several sedimentological and theoretical methods have been proposed to differentiate tsunami and storm wave affected boulders, no appropriate numerical method exists for their differentiation. Therefore, we developed a new numerical scheme to differentiate tsunami and storm wave boulders for coastal boulders on Ishigaki Island, Japan. In this area, tsunami and storm waves have emplaced numerous boulders on the reef and the coast. By conducting numerical calculations of storm waves in this region, we estimated the size of a storm wave that can explain the maximum clast size distribution of boulders on the reef. Consequently, we showed that a wave with a combination of 8 m in initial wave height and 10 s period can satisfy the above conditions when we assume mean sea level. In contrast to the boulders on the reef, all boulders deposited along the shore are heavier than the calculated possible maximum clast size distribution by the storm wave. Therefore, we confirmed these boulders as being of tsunami origin. Results of previous studies showed that they were most likely deposited or reworked by the 1771 Meiwa tsunami. Then, using the tsunami boulders, we numerically estimated the wave period and amplitude of the 1771 Meiwa tsunami, which should have had a 4–5 min period and 5.6–5.9, 6.3–7.0 m amplitude, respectively. Using the proposed scheme, it is possible to differentiate tsunami and storm wave boulders and estimate the size of past storm waves and tsunami waves, although it is noteworthy that there are exceptions for which the scheme cannot be applied.  相似文献   

Relative importance of multiple environmental variables in structuring benthic macroinfaunal assemblages in chronically metal-polluted salt marshes   总被引：1，自引：0，他引：1  

Daisuke Goto  William G. Wallace 《Marine pollution bulletin》2010,60(3):363-375

In this study, we assessed importance of sediment-associated trace metals in structuring benthic macroinfaunal assemblages along multiple environmental gradients in chronically polluted salt marshes of the Arthur Kill - AK (New York, USA). More than 90% of benthic macroinfaunal communities at the northern AK sites consisted of a considerably large number of only a few polychaete and oligochaete species. Approximately 70% of among-site variances in abundance and biomass of benthic macroinfaunal communities was strongly associated with a few environmental variables; only sediment-associated mercury consistently contributed to a significant proportion of the explained variances in species composition along natural environmental gradients (e.g., salinity). Although sediment-associated copper, lead, and zinc were substantially elevated at some of the AK sites, their ecological impacts on benthic macroinfaunal communities appeared to be negligible. These findings suggest that cumulative metal-specific impacts may have played an important role in structuring benthic macroinfaunal communities in chronically polluted AK ecosystems.  相似文献   

Simulations of measures to control lava flows     

Eisuke Fujita  Masataka Hidaka  Akio Goto  Susumu Umino 《Bulletin of Volcanology》2009,71(4):401-408

We evaluated the quantitative effects of artificial barriers, water-cooling and guiding channels on lava flow using the lava simulation program LavaSIM. Lava flow is basically subject to the topography around the path, effusive rate and viscosity. To prevent damage due to lava flow, we conducted experiments in controlling the flow direction, velocity and temperature. The simulation demonstrated that artificial barriers can successfully change the direction of a lava flow and is more effective when placed nearly parallel to the flow direction at a point where the topography is not very steep, while a barrier placed perpendicular to the flow direction can only stop the flux temporarily, ultimately allowing the solidified crust to accumulate and causing the following mass to go over the barrier. The water-cooling trial was also effective in controlling the direction and temperature, although the amount of water was as much order as 10⁵ m³. The guiding channels successfully control the direction and inundated area but only in local areas.  相似文献   

Effects of the 2011 Tohoku-oki tsunami and human activities on long-term coastal geomorphic development in northeastern Tohoku,Japan     

Haruki Imura  Kazuhisa Goto  Kenta Minamidate  Naoto Koiwa 《地球表面变化过程与地形》2024,49(2):949-963

The 2011 Tohoku-oki tsunami caused large-scale topographic changes along the Pacific coast of northeastern Japan. More than 10 years have passed since the tsunami waves struck the area. Today, because of reconstruction work, very few places exist where natural post-tsunami topographic changes can be monitored continuously. For this study, the authors investigated topographic changes caused not only by the 2011 tsunami but also by natural and artificial activities during the 50 years before and after the tsunami based on aerial photographs, excavations and subsurface explorations using ground-penetrating radar at the Osuka coast in Aomori prefecture, Japan. The site is rare because it is a protected area with few and superficial engineering activities, making it suitable for continuous observation of pre-tsunami, syn-tsunami and post-tsunami topographic changes. The findings indicate that the 2011 tsunami waves generated large topographic changes: depositional and erosional features produced by the tsunami can be recognized, respectively, as tsunami deposits and erosional channels across the sand dunes. During the post-tsunami phase, the sand volume at the coast quickly recovered naturally. Tsunami deposits and the erosional channels were well preserved underground even at 10 years after the event. However, dynamic movement of the dunes started after the tsunami. The shifting was attributable to the artificial clearing of coastal forests rather than the tsunami effects on the coast. Our results first indicate not only that the sedimentary features of paleo-tsunamis but also the erosional features have some probability of being preserved in the subsurface of the beach and sand dunes at tsunami-affected areas. Also, artificial activities such as deforestation are much more crucially undermining of the stability of the coastal geomorphology than the tsunami effects: the coast is now reaching a different status from its pre-tsunami situation.  相似文献   

Modeling boulder transport by coastal waves on cliff topography: Case study at Hachijo Island,Japan     

Masashi Watanabe  Kazuhisa Goto  Fumihiko Imamura  Andrew Kennedy  Daisuke Sugawara  Norihiro Nakamura  Takayuki Tonosaki 《地球表面变化过程与地形》2019,44(15):2939-2956

Clifftop coastal boulders transported by storm waves or tsunamis have been reported around the world. Although numerical calculation of boulder transport is a strong tool for the identification of tsunami or storm boulders, and for estimation of the wave size emplacing boulders, models which can reasonably solve boulder transport from below a cliff or from a cliff-edge onto a cliff-top do not yet exist. In this study, we developed a new numerical formulation for cliff-top deposition of boulders from the cliff edge or below the cliff, with validation from laboratory tests. We then applied the model using storm and tsunami wave forcing to simulate the observed boulder deposits at the northwest coast of Hachijo Island, Japan. Using the model, the actual distribution of boulders was explained well using a reasonable storm wave height without assumption of anomalously high-water level by storm surge. Results show that boulder transport from the cliff edge or under the cliff onto the cliff-top was possible from a tsunami with periods of 5~10 min or storm waves with no storm surge. However, the actual distribution of boulders on the cliff was explained only by storm waves, but not by tsunami. Therefore, the boulders distributed at this site are likely of storm wave origin. Our developed model for the boulder transport calculation can be useful for identifying a boulder's origin and can reasonably calculate cliff-top deposition of boulders by tsunami and storm waves. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.  相似文献