Accuracy of quantized Voronoi diagrams     

Yukio Sadahiro  Takashi Tominaga 《International journal of geographical information science》2013,27(10):1173-1189

Quantization of spatial objects, which usually means vector‐to‐raster conversion in GIS and remote sensing, is a basic operation used for handling spatial data from data creation to visualization. Since quantization is an approximation of spatial objects, it inevitably yields errors in measuring their properties such as area, perimeter, diameter, and so forth. This paper discusses the accuracy of a quantized Voronoi diagram, a spatial tessellation generated from a set of points. A measure is proposed to evaluate the accuracy of the area of Voronoi regions calculated after quantization. In one‐dimensional space the measure is expressed as an explicit function of the expected number of generators in a cell. In two‐dimensional space, on the other hand, the measure is defined by an implicit function, whose approximation is derived in an explicit form. These functions permit us to evaluate the accuracy of quantization in relation to the size of lattice cells and the density of Voronoi generators. This leads to an appropriate choice of a lattice to keep the quality of a quantized Voronoi diagram at a desirable level.  相似文献   

Analysis of the appearance and disappearance of point objects over time     

Yukio Sadahiro 《International journal of geographical information science》2019,33(2):215-239

The appearance and disappearance of immovable points are important spatiotemporal events in geographical information science. They represent phenomena such as the birth and death of trees in forests, construction and destruction of buildings in cities and openings and closures of shops and restaurants. This paper proposes a new method for analyzing the appearance and disappearance of points. The method helps analysts capture the overall picture and regional variation of event pattern and detecting significant local patterns. Four measures are defined that indicate the intensity of spatial and temporal patterns of events. The measures are visualized as grid maps. A statistical test is used to evaluate the significance of the measures to extract the regions of significant patterns. The proposed method is applied in an analysis of shops and restaurants in Shibuya, Tokyo. Technical soundness of the method is discussed along with empirical findings.  相似文献   

A numerical investigation of eddy-induced chlorophyll bloom in the southeastern tropical Indian Ocean during Indian Ocean Dipole—2006     

Iskhaq Iskandar  Hideharu Sasaki  Yoshikazu Sasai  Yukio Masumoto  Keisuke Mizuno 《Ocean Dynamics》2010,60(3):731-742

An eddy-resolving coupled physical–biological model is used to study the effect of cyclonic eddy in enhancing offshore chlorophyll-a (Chl-a) bloom in the southeastern tropical Indian Ocean during boreal summer–fall 2006. The results demonstrate that the offshore Chl-a blooms are markedly coincident with the high eddy kinetic energy. Moreover, the vertical variations in Chl-a, nitrate, temperature, and mixed-layer depth (MLD) strongly imply that the cyclonic eddies induce surface Chl-a bloom through the injection of nutrient-rich water into the upper layer. Interestingly, we found that the surface bloom only occurs when the deep Chl-a maximum is located within the MLD. On the other hand, the response of subsurface Chl-a to the eddy pumping is remarkable, although it is hardly observable at the surface.  相似文献   

Comment on “Evaluation of palaeo-oxygenation of the ocean bottom cross the Permian–Triassic boundary” by Kakuwa (2008): Was the Late Permian deep-superocean really oxic?     

Yasuhiro Kato  Yukio Isozaki 《Global and Planetary Change》2009,69(1-2):79-81

Nearly 15 years after the proposal of the superanoxia concept (Isozaki, Y., 1994. Superanoxia across the Permo–Triassic boundary: record in accreted deep-sea pelagic chert in Japan. In: Embry, A.F., Beauchamp, B., Glass, D.J. (Eds.), Pangea: Global Environments and Resources. Memoir, Canadian Society of Petroleum Geologists, 17, pp. 805–812.), it is an appropriate timing to re-evaluate its geological context with the updated dataset. Kakuwa (Kakuwa, Y., 2008. Evaluation of palaeo-oxygenation of the ocean bottom across the Permian–Triassic boundary. Global and Planetary Change 63, 40–56.) lately discussed that the deep-sea anoxia across the Permian–Triassic boundary (P–TB) may have been much shorter than previously proposed, on the basis of ichnofabrics and geochemical data; however, his interpretations of the data do not appear straightforward nor persuading, and thus his claim is likely misled. Here we raise comments to his explanation on the following four issues: 1) invalid application of ichnofabric indices for shallow sea sediments to deep-sea cherts, 2) misinterpretation of Ce anomaly as a redox indicator, 3) improper application of various redox sensitive trace elements, and 4) questionable interpretations of δ³⁴S data of pyrites.  相似文献   

Impacts of the South China Sea Throughflow on seasonal and interannual variations of the Indonesian Throughflow   总被引：3，自引：0，他引：3  

Tomoki Tozuka  Tangdong Qu  Yukio Masumoto  Toshio Yamagata   《Dynamics of Atmospheres and Oceans》2009,47(1-3):73-85

Impacts of the South China Sea Throughflow (SCST) on seasonal and interannual variations of the Indonesian Throughflow are studied by comparing outputs from ocean general circulation model (OGCM) experiments with and without the SCST. The observed subsurface maximum in the southward flow through the Makassar Strait is simulated only when the SCST, which is driven by the large-scale wind, is allowed in the model. The mean volume and heat transport by the Makassar Strait Throughflow are reduced by 1.7 Sv and 0.19 PW, respectively, by the existence of the SCST in the model. The difference is particularly remarkable during boreal winter when the SCST reaches its seasonal maximum. Furthermore, the SCST is strengthened during El Niño, leading to the weakening in the southward volume and heat transport through the Makassar Strait by 0.37 Sv and 0.05 PW, respectively. These findings from the OGCM experiments suggest that the SCST may play an important role in climate variability of the Indo-Pacific Ocean.  相似文献   

Orogeny of the Japanese Islands     

G. Kimura  Y Isozaki  S. Maruyama 《Island Arc》1996,5(3):215-215

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Comparative Measurements Of Co2flux Over A Forest Using Closed-Path And Open-Path Co2analysers     

Yukio Yasuda  Tsutomu Watanabe 《Boundary-Layer Meteorology》2001,100(2):191-208

An eddy covariance system using a closed-path CO₂analyser was constructed for long-term CO₂flux measurements above a forest, and its total frequency response was valuated experimentally. The amplitude and phase responses of the system wereexamined through a preliminary test, in which a prescribed pattern of CO₂fluctuation was input to the system. The result showed that the amplitude of the output from the system was attenuated as frequency increased, with a half-power frequency of 0.3 Hz. The phase was delayed by the air sampling through a long tube, but the delay in phase decreased asfrequency increased. We then presented a new technique for the correction of flux loss due to the inadequate system response for the eddy covariance measurements of CO₂ flux. Using the present system and the correction technique, diurnal variations in CO₂ flux were measured over a temperate deciduous forest on three days in 1997. The results were compared with the CO₂fluxes measured with a fast response open-path gas analyser. The CO₂fluxes from the closed-path system agreed with those from the open-path system after the Webb, Pearman and Leuning correction was made for the latter. In the present test over a forest, the contribution of the frequency-response correction to the CO₂fluxes was small and its averaged percentage was only 3%in the daytime. However, the percentage would likely increase, if the system were applied to a shorter vegetation site where high frequency components are more important. The comparison confirmed that we can obtain correct measurements of CO₂flux using the present closed-path system and the correction technique.  相似文献   

A stochastic model of earthquake occurrence and the accompanying horizontal land deformation     

Yukio Hagiwara 《Tectonophysics》1975,26(1-2)

A large-scale earthquake is believed to be associated with a release of strain energy accumulated in the crust, probably by the motion of upper-mantle lithosphere. Such an earthquake mechanism is well simulated by a belt-conveyer model proposed by Utsu (1972). The probability of earthquake occurrence can be estimated on the assumption that the motion of a slider on the belt-conveyer is mathematically formulated as a Markov process.In the probabilistic expressions, the results of Mogi's (1962) rock-fracture experiments are applied to the hazard-rate function of earthquake occurrence. The hazard-rate function has two coefficients, A and B, to be determined by the experiments. It is concluded that, when B is small, a number of small-scale earthquakes occur in the early time after the accumulation of crustal strain energy starts, but that the accumulated strain energy changes catastrophically into a single large-scale earthquake, when B is large.  相似文献   

Geodesy in Japan     

Yukio Hagiwara 《Surveys in Geophysics》1974,1(3):305-323

T. Inoh was the first who completed a nation-wide map of Japan, in the beginning of the 19th century. He determined geodetic positions by distance and angle measurements and by astronomical observations. When Japan entered into its modern era, about 100 years ago, the Military Land Survey was established and has conducted geodetic work in Japan ever since until the end of World War II. A German surveying system belonging to Helmert's school was adopted. The Ministry of Education organized later the Geodetic Commission which promoted the geodetic activities in cooperation with the Military Land Survey. Comparison between the first and second nation-wide triangulation results obtained by the Geographical Survey Institute (GSI), the successor of the Military Land Survey, brought out marked horizontal land-deformations associated with a large earthquake. Repetitions of levelling survey also make it clear that vertical land-movements, well consistent with tide-gauge observation data, take place in association with earthquakes. The extensive subsidence in the Northeast Japan may be explained by assuming a sinking lithosphere, as is argued by the theory of plate tectonics. On the other hand, most local movements are closely correlated to pre-, co- and post-seismic land-deformations. The nation-wide gravity survey carried out by the GSI disclosed a complicated gravity distribution in Japan. Ship-borne gravimeters have now been extensively working at sea. One of the recent highlights of gravimetric work is the detection of secular gravity changes which are in accordance with the secular changes of levelling data. A portable absolute-gravity measuring instrument was constructed by the Earthquake Research Institute although it is still in a testing stage. Much advance has been made in the astrogeodetic observation devices since 1950's.  相似文献   

A catalytic oxidation method for the determination of total nitrogen dissolved in seawater     

Yoshimi Suzuki  Yukio Sugimura  Tadamasa Itoh 《Marine Chemistry》1985,16(1):83-97

A detailed examination of a high-temperature catalytic oxidation method for liquid samples in the analysis of total nitrogen dissolved in seawater is reported. The nitrogenous compounds in liquid samples are oxidized on a platinum catalyzer at 680°C under oxygen atmosphere and the generated NO₂ is absorbed into a chromogenic reagent, followed by a spectrophotometric determination. The results of this method are much higher than those of wet oxidation methods. Molecular size dependency of the results clearly indicates that the above discrepancy is caused by the low oxidation capacity of the wet oxidation method against high-polymer organic matter dissolved in seawater. The results revealed that the concentration of total nitrogen in seawater is nearly constant from surface to bottom, ranging from 30 to 40 μM 1^?1, which organic nitrogen concentration higher in the surface layer, and a rapid decrease with depth. An examination of molecular size distribution indicates that the concentration of high-polymer organic nitrogen decreases rapidly from surface to deeper layers, with molecular sizes ranging from 5 × 10³ to 3 × 10⁴. Because of the well-defined principle of the oxidation process, its reliability, ease of sample handling and of analytical procedure on board or in the land laboratory, the present method is much more suitable for the marine analytical chemistry of total and organic nitrogen than the other previous methods.  相似文献