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Removal of water‐surface reflection effects with a temporal minimum filter for UAV‐based shallow‐water photogrammetry 
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下载免费PDF全文 I GD Yudha Partama Ariyo Kanno Motoyasu Ueda Yoshihisa Akamatsu Ryutei Inui Masahiko Sekine Koichi Yamamoto Tsuyoshi Imai Takaya Higuchi 《地球表面变化过程与地形》2018,43(12):2673-2682
The recent development of structure‐from‐motion (SfM) and multi‐view stereo (MVS) photogrammetry techniques has enabled semi‐automatic high‐resolution bathymetry using aerial images taken by consumer‐grade digital cameras mounted on unmanned aerial vehicles (UAVs). However, the applicability of these techniques is sometimes limited by sun and sky reflections at the water surface, which render the point‐cloud density and accuracy insufficient. In this research, we present a new imaging technique to suppress the effect of these water‐surface reflections. In this technique, we order a drone to take a short video instead of a still picture at each waypoint. We then apply a temporal minimum filter to the video. This filter extracts the smallest RGB values in all the video frames for each pixel, and composes an image with greatly reduced reflection effects. To assess the performance of this technique, we applied it at three small shallow‐water sites. Specifically, we evaluated the effect of the technique on the point cloud density and the accuracy and precision of the photogrammetry. The results showed that the proposed technique achieved a far denser point cloud than the case in which a randomly chosen frame was used for each waypoint, and also showed better overall accuracy and precision in estimating water‐bottom elevation. The effectiveness of this new technique should depend on the surface wave state and sky radiance distribution, and this dependence, as well as the applicability to large areas, should be investigated in future research. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
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一种基于真实身份的BBS系统实名保障技术 总被引：1，自引：0，他引：1
用户身份的真实性一直是BBS系统管理的重要方面之一。采用SAML协议,将跨域单点登录中的认证技术引入到BBS系统中,从而实现了用户采用真实身份登录BBS系统,保证了BBS用户的实名。并以多个高校的BBS系统作为样例,建立起基于真实身份的示范BBS系统。 相似文献
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A method is presented for determining bounds of the properties of axial symmetric bodies from a finite number of gravity and magnetic observations based on Parker's theory of ideal bodies. Bounds on the density contrast and the intensity of magnetization are calculated as a function of depth to the top of the anomalous source, restricting the range of smallest possible solutions to fit the data. The model studied is approximated by an array of vertical annuli cylinders, each of uniform density and magnetization. Linear programming algorithms based on the ideal body theory were used to calculate the distribution of these parameters within the body. Simultaneous inversion of gravity and magnetic data is performed assuming a constant ratio between the density contrast and the intensity of magnetization and that a common body is responsible for both observed fields. The parameter k(|J|/δp) provides information about the rock type of the structure. Interpretation of gravity and aeromagnetic data from Darnley Bay, NWT, Canada, indicated the presence of a shallow ultrabasic intrusion. 相似文献
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High hydrogen pressure pyrolysis (hydropyrolysis) was performed on samples of solvent extracted Kimmeridge Clay Formation
source rock with a maturity equivalent to ca. 0.35% vitrinite reflectance. We describe the types and distributions of organic nitrogen compounds in the pyrolysis products
(hydropyrolysates) using GC-MS. Compounds identified included alkyl-substituted indoles, carbazoles, benzocarbazoles, quinolines
and benzoquinolines. The distributions of the isomers of methylcarbazoles, C2-alkylcarbazoles and benzocarbazoles in the hydropyrolysates were compared to a typical North Sea oil. The hydropyrolysates
compared to the North Sea oil, showed increased contributions from alkylcarbazole isomers where the nitrogen group is "exposed"
(no alkyl substituents adjacent to the nitrogen functionality) and appreciable levels of benzo[b]carbazole relative to benzo[a]- and benzo[c]carbazoles. Hydropyrolysis is found to be an ideal technique for liberating appreciable quantities of heterocyclic organic
nitrogen compounds from geomacromolecules. The products released from the immature Kimmeridge Clay are thought to represent
a potential source of nitrogen compounds in the bound phase (kerogen) able to contribute to the free bitumen phase during
catagenesis. 相似文献
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Numerical investigations have been carried out on suitable interpretation schemes for gravity, based upon Backus-Gilbert inverse theory. A two-dimensional linear model consisting of horizontal prisms (grid shape) has been adopted for interpretation of gravity profiles. An inversion technique, which uses a linear approach suitable for rapid computation, and studies with synthetic bodies have led to improvements in the method, mainly by applying weighting factors, which improve the solution in the final stages of computational work. Gravity data from the well-known Cyprus island positive anomaly were inverted to demonstrate the feasibility of the method. 相似文献
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The Paran continental flood basalt province is a voluminousbimodal volcanic sequence, with <5% silicic rocks (‘rhyolites’)lying on top of the basalts, concentrated towards the SouthAtlantic margin. Petrographically, the rhyolites have an anhydrousmineralogy (plagioclase, pyroxene, Fe–Ti oxides), and.two distinct groups are defined on the basis of phenocryst abundance.The Palmas group rhyolites are almost aphyric (<5% phenocrysts),in contrast to the plagioclase-rith Chapec group rhyolites(<25% phenocrysts). The plagioclase and clinopyroxene phenocrystsin the Palmas group rhyolites are rounded and poorly preserved,and are compositionally less evolved than those in the Chapecgroup. Calculated eruption temperatures are unusually high forsilicic magmas (950–1100C), and lie within the rangeof temperatures for the associated flood basalts. Chemically,the Palmas and Chapec group rhyolites are clearly distinguishable,with the most striking feature being the higher high field strengthelements, notably Ti, in the Chapec group. This mirrors thewell-documented low- and high-Ti division of the Paran basalts,and in addition there is a geographic correlation between thelow- and high- Ti basalt and rhyolite provinces, with high-Tivolcanics predominating in the north of the Paran Basin, andlow-Ti in the south. The Chapec group have Sr and Nd isotoperatios which overlap with those of the high-Ti basalts (87Sr/86Sr1300•705–0•708), whereas the Palmas group exhibita range towards high Sr isotope ratios (87Sr/86Sr130 0•714–0•727),continuing the trend of the low-Ti basalts to more radiogenicvalues. This suggests that assimilation of radiogenic materialhas occurred. Both rhyolite groups plot away from the isotopicfields for crustal basement types beneath the Paran, thus anorigin by simple crustal melting is discounted. Based on petrographic,chemical and isotopic data, petrogenetic models for the tworhyolite groups are developed, focusing on the clear geneticlink between the Palmas rhyolites and the low-Ti basalts, andthe Chapec rhyolites and the high-Ti basalts. The Chapec rhyolitesare modelled as partial melts ( 30%) of underplated high-Tibasalts, rather than fractionates, primarily because of thetime gap between eruption of the high-Ti basalts and Chapecrhyolites. However, the Palmas rhyolites are almost coeval withthe low-Ti basalts, and are modelled as the products of open-systemfractional crystallization from these low-Ti basaltic magmas.In addition, this low-Ti suite shows a continuous trend frombasalt to rhyolite in highly incompatible elements such as Zrand Hf consistent with a liquid line of descent, whereas thehigh-Ti magmas have a substantial gap in the concentration ofthese elements between the basalts and rhyolites. Experimentaldata support the derivation of both Paran rhyolite groups frombasaltic parents with moderately low water contents. Pressurecalculations suggest shallower ponding for the Palmas magmasthan for the Chapec magma (<5 kbar vs 5–15 kbar),and the style of eruption inferred for the two groups is explosive(rheoignimbritic) for the Palmas group, and effusive (lava flows)for the Chapec group. KEY WORDS: Paran; Brazil; rhyolits; petrogenesis; geochemistry
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