Mapping seagrass coverage and spatial patterns with high spatial resolution IKONOS imagery

Seagrass habitats in subtidal coastal waters provide a variety of ecosystem functions and services and there is an increasing need to acquire information on spatial and temporal dynamics of this resource. Here, we explored the capability of IKONOS (IKO) data of high resolution (4 m) for mapping seagrass cover [submerged aquatic vegetation (%SAV) cover] along the mid-western coast of Florida, USA. We also compared seagrass maps produced with IKO data with that obtained using the Landsat TM sensor with lower resolution (30 m). Both IKO and TM data, collected in October 2009, were preprocessed to calculate water depth invariant bands to normalize the effect of varying depth on bottom spectra recorded by the two satellite sensors and further the textural information was extracted from IKO data. Our results demonstrate that the high resolution IKO sensor produced a higher accuracy than the TM sensor in a three-class % SAV cover classification. Of note is that the OA of %SAV cover mapping at our study area created with IKO data was 5–20% higher than that from other studies published. We also examined the spatial distribution of seagrass over a spatial range of 4–240 m using the Ripley’s K function [L(d)] and IKO data that represented four different grain sizes [4 m (one IKO pixel), 8 m (2 × 2 IKO pixels), 12 m (3 × 3 IKO pixels), and 16 m (4 × 4 IKO pixels)] from moderate-dense seagrass cover along a set of six transects. The Ripley’s K metric repeatedly indicated that seagrass cover representing 4 m × 4 m pixels displayed a dispersed (or slightly dispersed) pattern over distances of <4–8 m, and a random or slightly clustered pattern of cover over 9–240 m. The spatial pattern of seagrass cover created with the three additional grain sizes (i.e., 2 × 24 m IKO pixels, 3 × 34 m IKO pixels, and 4 × 4 m IKO pixels) show a dispersed (or slightly dispersed) pattern across 4–32 m and a random or slightly clustered pattern across 33–240 m. Given the first report on using satellite observations to quantify seagrass spatial patterns at a spatial scale from 4 m to 240 m, our novel analyses of moderate-dense SAV cover utilizing Ripley’s K function illustrate how data obtained from the IKO sensor revealed seagrass spatial information that would be undetected by the TM sensor with a 30 m pixel size. Use of the seagrass classification scheme here, along with data from the IKO sensor with enhanced resolution, offers an opportunity to synoptically record seagrass cover dynamics at both small and large spatial scales.     

Mapping species of submerged aquatic vegetation with multi-seasonal satellite images and considering life history information

Spatial information of the dominant species of submerged aquatic vegetation (SAV) is essential for restoration projects in eutrophic lakes, especially eutrophic Taihu Lake, China. Mapping the distribution of SAV species is very challenging and difficult using only multispectral satellite remote sensing. In this study, we proposed an approach to map the distribution of seven dominant species of SAV in Taihu Lake. Our approach involved information on the life histories of the seven SAV species and eight distribution maps of SAV from February to October. The life history information of the dominant SAV species was summarized from the literature and field surveys. Eight distribution maps of the SAV were extracted from eight 30 m HJ-CCD images from February to October in 2013 based on the classification tree models, and the overall classification accuracies for the SAV were greater than 80%. Finally, the spatial distribution of the SAV species in Taihu in 2013 was mapped using multilayer erasing approach. Based on validation, the overall classification accuracy for the seven species was 68.4%, and kappa was 0.6306, which suggests that larger differences in life histories between species can produce higher identification accuracies. The classification results show that Potamogeton malaianus was the most widely distributed species in Taihu Lake, followed by Myriophyllum spicatum, Potamogeton maackianus, Potamogeton crispus, Elodea nuttallii, Ceratophyllum demersum and Vallisneria spiralis. The information is useful for planning shallow-water habitat restoration projects.     

长江下游地区巨厚砂层中钻孔灌注桩施工技术

根据张家港、扬州等地砂层中施工钻孔灌注桩的实践，论述了巨厚砂层对施工的影响，指出必须采取配制优质泥浆、建立科学的泥浆循环系统、选择合适的钻具及钻进参数、进行孔径检查、提高灌注效率等技术措施，介绍了在砂层施工中应注意的问题和有效处理埋钻事故的方法。     

Simulation of diffraction of ocean waves by a submerged sphere in finite depth

Based on the linear diffraction theory, an investigation is made on the interaction of water waves with a completely submerged sphere in water of finite depth in this paper. The method of multipole expansions is used to obtain the fluid velocity potential in the form of double series of the associated Legendre functions with the unknown coefficients of the infinite set of infinite matrix equations. The truncation property of the matrices and the convergence of the multipole series coefficients are investigated for various wavelengths and depths. The systematic numerical simulation, based on our analytical solution, is carried out and the fields of the hydrodynamic diffraction pressure and fluid velocity around the sphere, the three-dimensional free surface elevation, and total exciting forces acting on the sphere are graphically presented for a wide range of the body submergences, ocean depths and wavelengths.     

A theory for waves interacting with porous structures with multiple regions

This study presents an analytical solution for the problem of waves passing a submerged porous structure, using a multi-region method in the solution scheme considering the characteristics of geometry and composing materials of the porous structure. Using the flux and pressure conditions on horizontal boundaries and interfaces, the orthogonal property of wave motion within the porous layers through water depth is derived, and applied in the solution process. The flux and pressure conditions on vertical boundaries and interfaces are integrated to give a set of linear matrix equations, through which the unknown coefficients are solved. Comparisons of the present method with previous studies are preceded in verification, which suggests the validity and practicability of the present study, with a further expectation of extending our work to build a mild-slope equation over multiple-layer porous medium in the future.     

Wave transformation over submerged permeable breakwater on porous bottom

A numerical model is presented in this study to investigate the wave transformation over a submerged permeable breakwater on a porous slope seabed. For this purpose, the time-dependent mild-slope equation is newly derived for waves propagating over two layers of porous medium. This new mild-slope equation involves the parameters of the porous medium, and it is a type of hyperbolic differential equation, therefore numerically efficient. The validity of the present model is verified based on the comparisons with the previous experiments. The effects of the permeable properties of both the porous seabed and the submerged permeable breakwater are discussed in detail. The geometry of the submerged permeable breakwater to the wave transformation is also investigated based on the numerical solutions.     

SAR对南沙群岛暗礁的成像能力

介绍了合成孔径雷达（ＳＡＲ）的成像原理及南沙群岛潮流、波浪状况。通过研究潮流、波浪对海表面微尺度波的调制机理,结合两者ＥＲＳ－１ ＳＡＲ 图像论述了ＳＡＲ对南沙群岛暗礁具有成像能力。     

Flume tank studies to elucidate the fate and behavior of diluted bitumen spilled at sea

An economical alternative to conventional crudes, Canadian bitumen, harvested as a semi-liquid, is diluted with condensate to make it viable to transport by pipeline to coastal areas where it would be shipped by tankers to global markets. Not much is known about the fate of diluted bitumen (dilbit) when spilled at sea. For this purpose, we conducted dilbit (Access Western Blend; AWB and Cold Lake Blend; CLB) weathering studies for 13 days in a flume tank containing seawater. After six days of weathering, droplets detached from the AWB slick and were dense enough to sink in seawater. The density of CLB also increased, but at a slower rate compared to AWB, which was attributed to the high concentration of alkylated polycyclic aromatic hydrocarbons in it, which are more resistant to weathering. An empirical, Monod-type model was introduced and was found to closely simulate the increase in oil density with time. Such a model could be used within oil spill models.     

2012年6·29贵州岑巩龙家坡滑坡灾害的基本特征与成因机理:一个由侧向剪切扰动诱发大型滑坡的典型案例

侧向剪切扰动诱发滑坡是一种新型滑坡类型,深入研究其成因机理,有助于开展滑坡预警工作。2012年6月29日6时20分左右,贵州省岑巩县思旸镇龙家坡山体发生大规模滑坡,300～400万 m³岩土体失稳后堵塞坡下的马坡河,形成20余 m高的堰塞坝及库容达7万余 m³的堰塞湖。笔者在对灾害现场进行详细地质调查的基础上,结合现场调绘、航拍、颗分试验等手段,对龙家坡滑坡的基本特征进行了分析研究,对滑坡发生及成灾原因进行了初步分析。结果表明:滑坡区风化破碎的厚层堆积体、有利的岩层倾向以及前缘临空是滑坡发生的基本条件;滑坡区南侧地下水径排区被堆填大量粉黏土弃渣,不仅为该区斜坡人为增加了巨大推力,还使该区斜坡地下水局部富集。在强降雨条件下,南侧堆积区首先发生滑动,其对主滑体的侧向剪切扰动作用带动主滑区大规模失稳破坏。由此,对这类侧向剪切扰动诱发的滑坡,在进行地质灾害调查和预警时,除了应调查其岩土体特征外,还必须查明其边界条件。     

钙离子添加对沉水植物菹草(Potamogeton crispus L.)和金鱼藻(Ceratophyllum demersum L.)富集水体磷的影响

沉水植物光合作用形成的微环境有利于水体中钙和磷形成CaCO_3-P共沉淀,从而将水体中的磷永久性去除,避免植物腐烂后的二次污染但不同的沉水植物种类形成CaCO_3-P共沉淀的能力不同本文以沉水植物菹草(Potamogeton crispus L)和金鱼藻(Ceratophyllum demersum L)为实验对象,研究水体中添加钙离子(0、100 mg/L)对水体磷(磷浓度:0、0.2、2 mg/L)的去除和植物富集磷的差异,并通过植物灰分磷的组分分析,聚焦植物钙磷的变化,为生态修复中沉水植物的选择提供理论依据结果表明:(1)菹草和金鱼藻体系中总磷(TP)和溶解性反应磷(SRP)浓度显著下降,添加钙离子使降幅升高,且菹草体系中水体TP和SRP降幅均高于金鱼藻TP和SRP降幅;(2)菹草的干重全磷在高磷低钙(2-0)水平最高,灰分总磷在高磷高钙(2-100)水平最高,而金鱼藻干重全磷在高磷高钙(2-100)水平最高,灰分总磷在中等磷低钙(0.2-0)水平最高;(3)在2 mg/L的磷浓度下,添加钙离子使菹草的钙磷(HCl-P)和水溶性磷(H_2O-P)含量升高,有机磷(NaOH-P)含量降低,结果使灰分总磷含量升高,而金鱼藻NaOH-P升高,HCl-P和H_2O-P含量均降低,结果使灰分总磷降低这表明菹草通过提高吸附性磷和钙磷含量增强磷的富集,而金鱼藻则只显著升高了灰分中有机磷的含量显然,水体富营养化背景下,相较于金鱼藻,菹草具有更强的形成CaCO_3-P共沉淀的能力,具备竞争优势.