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The hydrodynamics of a small tributary channel and its adjacent mudflat is studied in Willapa Bay, Washington State, USA. Velocity profiles and water levels are simultaneously measured at different locations in the channel and on the mudflat for two weeks. The above tidal flat and channel hydrodynamics differ remarkably during the tidal cycle. When the water surface level is above the tidal flat elevation, the channel is inactive. At this stage, the above tidal flat flow is predominantly aligned along the Bay axis, oscillating with the tide as a standing wave with peak velocities up to 0.3 m/s. When the mudflat becomes emergent, the flow concentrates in the channel. During this stage, current velocities up to 1 m/s are measured during ebb; and up to 0.6 m/s during flood. Standard equations for open-channel flow are utilized to study the channel hydrodynamics. From the continuity equation, a lateral inflow is predicted during ebb, which likely originates from the drainage of the mudflat through the lateral runnels. Both advective acceleration and lateral discharge terms, estimated directly from the velocity profiles, play a significant role in the momentum equation. The computed drag coefficient for bottom friction is small, due to an absence of vegetation and bottom bedforms in the channel. Sediment fluxes are calculated by combining flow and suspended sediment concentration estimated using the acoustic backscatter signal of the instruments. A net export of the sediment from the channel is found during ebb, which is not balanced by the sediment import during flood. When the mudflat is submerged, ebb-flood asymmetries in suspended sediment concentration are present, leading to a net sediment flux toward the inner part of the Willapa Bay. Finally, a residual flow is detected inside the channel at high slack water, probably associated with the thermohaline circulation. 相似文献
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Dhaval Vyas N.S.R. Krishnayya K.R. Manjunath S.S. Ray Sushma Panigrahy 《International Journal of Applied Earth Observation and Geoinformation》2011
There is an urgent necessity to monitor changes in the natural surface features of earth. Compared to broadband multispectral data, hyperspectral data provides a better option with high spectral resolution. Classification of vegetation with the use of hyperspectral remote sensing generates a classical problem of high dimensional inputs. Complexity gets compounded as we move from airborne hyperspectral to Spaceborne technology. It is unclear how different classification algorithms will perform on a complex scene of tropical forests collected by spaceborne hyperspectral sensor. The present study was carried out to evaluate the performance of three different classifiers (Artificial Neural Network, Spectral Angle Mapper, Support Vector Machine) over highly diverse tropical forest vegetation utilizing hyperspectral (EO-1) data. Appropriate band selection was done by Stepwise Discriminant Analysis. The Stepwise Discriminant Analysis resulted in identifying 22 best bands to discriminate the eight identified tropical vegetation classes. Maximum numbers of bands came from SWIR region. ANN classifier gave highest OAA values of 81% with the help of 22 selected bands from SDA. The image classified with the help SVM showed OAA of 71%, whereas the SAM showed the lowest OAA of 66%. All the three classifiers were also tested to check their efficiency in classifying spectra coming from 165 processed bands. SVM showed highest OAA of 80%. Classified subset images coming from ANN (from 22 bands) and SVM (from 165 bands) are quite similar in showing the distribution of eight vegetation classes. Both the images appeared close to the actual distribution of vegetation seen in the study area. OAA levels obtained in this study by ANN and SVM classifiers identify the suitability of these classifiers for tropical vegetation discrimination. 相似文献
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矿产资源的持续开采与加工利用使得矿区周边水资源受到的污染日趋严重,急需采用先进技术对水污染进行监测分析,遥感技术是水环境监测最为有效的技术之一。利用国产环境一号小卫星多光谱遥感影像数据,针对福建省龙岩市紫金山矿区不同时相的数据进行水质遥感监测。利用近红外单波段阈值分割法提取悬浮物浓度信息,基于矿区酸碱性水体光谱曲线特性采用342波段假彩色合成影像,采用SVM分类方法进行分类,判别矿区水体酸碱性以及分析水体受污染程度变化和污染源。结果表明,研究区汀江水体2008年呈现碱性,2010年呈现弱碱性,水质在研究时段内得到一定的改善,但在选矿厂与矿区附近的水体中仍含有大量重金属沉积物。 相似文献
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