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In order to gain insight into the formation dynamics of mudbanks off the Kerala coast of India, extensive surveying of the nearshore bathymetry along with sediment characterization was undertaken. The textural and geotechnical properties of the surficial sediments of a mudbank were determined during pre-monsoon, monsoon, and post-monsoon periods. The mudbank sediments were clayey silts with high water and organic carbon contents, high Atterberg limits, and low bulk density, and therefore very susceptible to entrainment. During the monsoon, the mudbank regime was characterised by enhanced turbidity and a benthic fluff layer, triggered by the increasing swell of the early monsoon period. Re-suspension exposed a more consolidated, previously sub-bottom, layer which exhibited lower water content and greater shear strength than the pre-monsoon seabed. Texturally, the monsoon seabed was similar to the pre-monsoon seabed, with the same modal grain size, but the proportions of sand and coarse silt increased nearshore, while the proportions of fine and very fine silt increased offshore. There was a seaward-fining textural gradient at all times, but this became pronounced during the monsoon period. Paradoxically, the monsoonal seabed displayed greatly reduced wet bulk density. It is hypothesized that this was due to the presence of gas, probably methane, in the sediments (while the pre-monsoon sediments were fully saturated, the monsoon sediments were only 83% saturated). We speculate that the gas was forced into the surficial sediments either by wave pumping (at the onset of the monsoon) or by seaward-flowing subbottom freshwater (derived from monsoonal rains). With the waning of the monsoon, the benthic fluid mud layer rapidly disappeared and the seabed returned to its pre-monsoon state as suspended sediments were redeposited. The mudbank regime is therefore essentially an in situ phenomenon. It is suggested that the mudbanks are palimpsest, marshy, lagoonal deposits, rich in organic matter and derived gas, that were submerged after a marine transgression. The surficial sediment is annually entrained during the monsoon, but erosion is limited by the formation of the benthic fluid mud layer, which attenuates wave generated turbulence. Although some fine sediment disperses alongshore and offshore, most is returned to the seabed as the monsoon declines. 相似文献
223.
基于多源水深数据融合的海底高精度地形重建 总被引:2,自引:0,他引:2
本文在研究多源水深数据构建技术的基础上,分析了张力样条插值算法和“移去-恢复”法的多源水深数据融合处理技术,基于该方法选取实验区,利用多波束、单波束、历史海图等多源水深数据进行高精度海底地形融合试验,并针对多源水深融合技术缺少误差评估的现状,利用split-sample方法对融合结果进行水深不确定性评估,形成融合结果的可靠性空间分布。结果表明该方法无论是在数据稀疏区还是高密度区都达到了较好的融合效果,既保留了高分辨率水深数据的细节信息,又较真实的反映了研究区海底地形特征,且构建的海底地形精度可靠,误差百分比集中在0.5%。本文整套数据融合和结果评估方法可为多源水深数据融合的海底高精度地形构建提供借鉴和参考。 相似文献
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基于半经验遥感模型,开展广东省雷州湾SPOT-5影像不同水深范围的遥感反演及误差分析,给出不同模型对应的最佳水深范围和不同水深范围的最佳反演模型,结果如下:红光单波段模型、红光-绿光双波段模型、绿光-红光-近红外三波段模型均在2~5m水深范围内反演误差最小,分别为16.7%,13.2%和17.1%。0~2m水深范围内,红光-近红外双波段模型反演误差最小,为34.3%;2~5m水深范围内,红光-绿光双波段模型反演误差最小,为13.2%;5~10m水深范围内,红光-近红外双波段模型反演误差最小,为19.3%;10~20m水深范围内,三波段模型反演误差最小,为31.5%。 相似文献
226.
A video-based technique for mapping intertidal beach bathymetry 总被引:2,自引:0,他引:2
Stefan G. J. Aarninkhof Ian L. Turner Thomas D. T. Dronkers Mark Caljouw Leann Nipius 《Coastal Engineering》2003,49(4):275
Measuring the location of the shoreline and monitoring foreshore changes through time are core tasks carried out by coastal engineers for a wide range of research, monitoring and design applications. With the advent of digital imaging technology, shore-based video systems provide continuous and automated data collection, encompassing a much greater range of time and spatial scales than were previously possible using field survey methods.A new video-based technique is presented that utilises full-colour image information, which overcomes problems associated with previous grey-scale methods, which work well at steep (reflective) sites, but are less successful at flatter (dissipative) sites. Identification of the shoreline feature is achieved by the automated clustering of sub-aqueous and sub-aerial pixels in ‘Hue–Saturation–Value’ (HSV) colour space, and applying an objective discriminator function to define their boundary (i.e., ‘shoreline’) within a time-series of consecutive geo-referenced images. The elevation corresponding to the detected shoreline features is calculated on the basis of concurrent tide and wave information, which is incorporated in a model that combines the effects of wave set-up and swash, at both incident and infragravity frequencies.Validation of the technique is achieved by comparison with DGPS survey results, to assess the accuracy of the detection and elevation methods both separately and together. The uncertainties associated with the two sub-components of the model tend to compensate for each other. The mean difference between image-based and surveyed shoreline elevations was less than 15 cm along 85% of the 2-km study region, which corresponded to an horizontal offset of 6 m. The application of the intertidal bathymetry mapping technique in support of CZM objectives is briefly illustrated at two sites in The Netherlands and Australia. 相似文献
227.
南黄海辐射沙脊群海域的水深遥感 总被引:5,自引:1,他引:5
南黄海的辐射沙脊群海域地形地貌复杂多变,应用遥感技术来测量其水下地形不仅有可能,而且势在必行。在对沿海及长江口门内外遥感反演水下地形研究的基础上,选择沙脊群海域中有代表性的一块水域为研究区,同步测量其水下地形和水流、悬沙含量,用实测地形和MODIS影像数据建立水深反演模型,同时分析该区域的悬沙光谱特征,选择悬沙遥感参数,以MODIS数据的水深反演模型和沙脊群水域的悬沙遥感参数为依据,建立削弱悬沙影响的水深遥感模型,从而反演出1.5×104km2的辐射沙脊群水下地形。从反演结果看,所建模型的相关系数二次方的值为0.664,F-值为18662,平均绝对误差为1.52m,平均相对误差为24%,5~15m水深段的平均相对误差只有18%,反演效果较好。 相似文献
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229.
This paper demonstrates a practical step-wise method for modelling wave energy at the landscape scale using GIS and remote sensing techniques at Alphonse Atoll, Seychelles. Inputs are a map of the benthic surface (seabed) cover, a detailed bathymetric model derived from remotely sensed Compact Airborne Spectrographic Imager (CASI) data and information on regional wave heights. Incident energy at the reef crest around the atoll perimeter is calculated as a function of its deepwater value with wave parameters (significant wave height and period) hindcast in the offshore zone using the WaveWatch III application developed by the National Oceanographic and Atmospheric Administration. Energy modifications are calculated at constant intervals as waves transform over the forereef platform along a series of reef profile transects running into the atoll centre. Factors for shoaling, refraction and frictional attenuation are calculated at each interval for given changes in bathymetry and benthic coverage type and a nominal reduction in absolute energy is incorporated at the reef crest to account for wave breaking. Overall energy estimates are derived for a period of 5 years and related to spatial patterning of reef flat surface cover (sand and seagrass patches). 相似文献
230.