全数字摄影测量系统与MicroStation联机测图     

葛凤仪 《海洋测绘》2007,27(2):65-67

论述了全数字摄影测量系统(DPS)与MicroStation联机测图的方法,以及与此相关的层控对应表的制作.以实际生产作业为例,有效地提高了工作效率,降低内耗,减少了作业中间数据的相互转换,避免了有效数据的丢失,很好地保证了产品的质量.  相似文献   

An assessment model for the fate and environmental effects of offshore drilling mud discharges   总被引：1，自引：0，他引：1  

Charles G. Hannah  Adam Drozdowski  John Loder  Kee Muschenheim  Tim Milligan 《Estuarine, Coastal and Shelf Science》2006,70(4):577

The benthic boundary layer transport (bblt) model was developed to assess potential impact zones from drilling mud discharges from offshore oil and gas drilling. The model focuses on the drift, dispersion and concentration levels of the suspended fraction of the drilling mud fines in the benthic boundary layer with the assumption of a spatially homogeneous environment. The current version of the model includes a wave boundary layer, a breakup module for drilling mud flocs, a dose–response module for scallops, and a graphical user interface (GUI). The GUI was written in Java which makes the code largely platform independent. Simulations of suspended barite concentration near Sable Island on the Scotian Shelf during drilling in the fall of 1999 reproduce the very low concentrations (generally less than 1 μg L⁻¹) observed during the Environmental Effects Monitoring program. However, the simulations also exhibited concentrations in excess of the no-effects concentration for scallops (100 μg L⁻¹) prior to the sampling program. The model estimates that the potential impact on scallops in the vicinity of the drilling is a few days of lost growth over scales of a few kilometers.  相似文献   

Mixed layer depth front and subduction of low potential vorticity water in an idealized ocean GCM   总被引：4，自引：0，他引：4  

Shiro Nishikawa  Atsushi Kubokawa 《Journal of Oceanography》2007,63(1):125-134

It is known that there is a front-like structure at the mixed layer depth (MLD) distribution in the subtropical gyre, which is called the MLD front, and is associated with the formation region of mode water. In the present article, the generation mechanism of the MLD front is studied using an idealized ocean general circulation model with no seasonal forcing. First, it is shown that the MLD front occurs along a curve where u _g ·∇T _s = 0 is satisfied (u _g is the upper ocean geostrophic velocity vector, T _s is the sea surface temperature and ∇ is the horizontal gradient operator). In other words, the front is the boundary between the subduction region (u _g ·∇T _s > 0) and the region where subduction does not occur (u _g ·∇T _s < 0). Second, we have investigated subduction of low potential vorticity water at the MLD front, which has been pointed out by past studies. Since u _g ·∇T _s = 0 at the MLD front, the water particles do not cross the outcrop at the MLD front. The water that is subducted at the MLD front has come from the deep mixed layer region where the sea surface temperature is higher than that at the MLD front. The temperature of the water in the deep mixed layer region decreases as it is advected eastward, attains its minimum at the MLD front where u _g ·∇T _s = 0, and then subducts under the warmer surface layer. Since the deep mixed layer water subducts beneath a thin stratified surface layer, maintaining its thickness, the mixed layer depth changes abruptly at the subduction location.  相似文献   

Measurements of atmospheric dimethyl sulfide and carbon disulfide in the western Atlantic boundary layer     

David J. Cooper  Eric S. Saltzman 《Journal of Atmospheric Chemistry》1991,12(2):153-168

Shipboard measurements of atmospheric dimethyl sulfide were made during two transects along the east coast of the United States and at several stations in the Gulf of Maine. Limited measurements of carbon disulfide and hydrogen sulfide are also reported. The mean DMS mixing ratio was 29 pptv (=25, n=84, median 19 pptv) during the Atlantic transects, and 101 pptv (=67, n=77, median 79 pptv) in the Gulf of Maine. Distinct diurnal variations were found in the DMS data from the transects. The meteorology of the study area appears to control day-to-day differences in the magnitude of these diurnal variations, although rapid daytime oxidation is suggested in some cases. Diurnal variations were also evident in near-shore stations in the Gulf of Maine due to nocturnal boundary-layer inversion. Diurnal variation was not evident at other sites in the Gulf due to large scale changes in the atmospheric circulation pattern, which effectively masked any effects due to oxidation processes. Model simulations confirm that the DMS levels and diurnal variation found during the transects are not consistent with atmospheric oxidation processes alone. Atmospheric CS₂ and H₂S mixing ratios were less than 3 pptv during the transects, except for a single period of higher CS₂ mixing ratios (reaching 11 pptv) during advection of continental air. Calculations of the flux of oceanic sulfur to the eastern United States show that the contribution of natural sulfur to the North American sulfur budget is small compared to anthropogenic sources.  相似文献   

华北地区三维地壳上地幔结构   总被引：40，自引：7，他引：33  

陈国英  庄真 《地球物理学报》1991,34(2):172-181

本文用均等显示滤波频时分析方法分析了长周期瑞利面波资料,获得了路经中国大陆及邻区的238条混合路径的面波群速度频散,其周期范围为10.5-113s.用改进的分格反演方法从混合路径频散中提取出位于华北地区的12个4°×4°网格单元的纯路径频散并反演其地壳上地幔结构.所得结果表明,华北地区地壳上地幔结构横向变化显著;从东向西地壳逐渐变厚;位于华北东部的分格在地壳中20km深处普遍存在低速层,整个华北地区上地幔低速层埋藏较浅,一般为55-100km之间.各个网格上地幔低速层的速度不尽相同.  相似文献   

Hydrochemical and sedimentary responses of paired High Arctic watersheds to unusual climate and permafrost disturbance,Cape Bounty,Melville Island,Canada     

Ted Lewis  Melissa J. Lafrenière  Scott F. Lamoureux 《水文研究》2012,26(13):2003-2018

High Arctic river responses to changing hydroclimatic and landscape processes are poorly understood. In non‐glacierized basins, snowmelt and rainfall generate river discharge, which provides first order control over fluxes. Further factors include the seasonality of precipitation, seasonal active layer development, and permafrost disturbance. These controls were evaluated in terms of sedimentary and biogeochemical fluxes from paired catchments at Cape Bounty, Melville Island, Nunavut during 2006–2009. Results indicate that the source of runoff can be more important than the amount of runoff for sediment, solutes, and organic yields. Although the snowmelt period is typically the most important time for these yields, heavy late summer precipitation events can create disproportionately large yields. Rainfall increases yields because it hydrologically connects areas otherwise isolated. Inorganic solute yields from late summer rainfall are higher because the thick active layer maximizes hydrologic interactions with mineral soils and generates high solute concentrations. Results also indicate that while the catchments are broadly similar, subtle topographic differences result in important inter‐catchment differences in runoff and suspended and dissolved loads. The East watershed, which had less extensive permafrost disturbance, consistently had higher concentrations of dissolved solids. These higher dissolved fluxes cannot therefore be explained by thermokarst features, but rather by deeper active layer development, due to a greater proportion of south‐facing slopes. Although warm temperatures in 2007 led to extensive active layer disturbance in the West watershed, because the disturbances were largely hydrologically disconnected, the total disturbed area was small, and inter‐annual variability in discharge was high, there was no detectable response in dissolved loads to disturbances. Sediment availability increased after 2007, but yields have largely returned to pre‐disturbance levels. Results indicate that seasonality and frequency‐magnitude characteristics of projected increases in precipitation must be considered along with active layer changes to predict the fluvial sedimentary and biogeochemical response to regional climate change. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

利用长期GPS数据研究2008年汶川地震震后形变     

贺克锋  赵斌  杜瑞林 《大地测量与地球动力学》2019,39(2):122-126

采用2008年汶川MW7.9地震震后7 a的GPS连续站和流动站的长期观测资料，基于粘弹性松弛模型，利用PSGRN/PSCMP程序计算汶川震后形变，反演巴颜喀拉块体下的粘弹性参数。其中分层模型考虑巴颜喀拉块体下存在低速带，最优拟合的粘弹性松弛模型显示该低速带粘弹性参数为2.51×1018 Pa·s，而中下地壳粘弹性参数为3.98×1018 Pa·s。  相似文献   

南海风生近惯性能通量的敏感性分析     

孙宝楠  连展  袁业立  徐海洋 《海洋学报(英文版)》2019,38(4):136-145

After validated by the in-situ observation, the slab model is used to study the wind-generated near-inertial energy flux(NIEF) in the South China Sea(SCS) based on satellite-observed wind data, and its dependence on calculation methods and threshold criteria of the mixed layer depth(MLD) is investigated. Results illustrate that the total amount of NIEF in the SCS could be doubled if different threshold criteria of MLD are adopted. The NIEF calculated by the iteration and spectral solutions can lead to a discrepancy of 2.5 GW(1 GW=1×109 W). Results also indicate that the NIEF exhibits spatial and temporal variations, which are significant in the boreal autumn,and in the southern part of the SCS. Typhoons are an important generator of NIEF in the SCS, which could account for approximately 30% of the annual mean NIEF. In addition, deepening of the MLD due to strong winds could lead to a decrease of NIEF by approximately by 10%. We re-estimate the annual mean NIEF in the SCS,which is(10±4) GW and much larger than those reported in previous studies.  相似文献   

北半球夏季中高纬海洋声散射层分布研究   总被引：1，自引：0，他引：1  

黄二辉  杨燕明  文洪涛  周鸿涛 《海洋学报》2019,41(7):52-64

利用第八次北极调查走航ADCP后向散射强度数据，结合太阳高度、海冰密集度和实测水体环境参数数据，统计分析了中高纬海洋声散射层的时空变化特征。结果表明，纬度越高，声散射层在海表滞留时间越短，即使在极昼期间及全海冰覆盖海域，虽然其迁移幅度和后向散射强度减弱，但仍受太阳高度变化影响，且二者具有较强的时序相关性；在北极中央海域，不仅声散射层迁移活动较弱，且出现无明显散射层的情况，可能是因为该海域浮游动物和鱼类聚集度相对较低且迁移活动微弱，超出了本文所用ADCP的探测精度范围；从鄂霍次克海至白令海西南海域，往返ADCP数据均显示有两个后向散射强度上高下低，但垂直迁移时间同步的声散射层，且二者间距随纬度增加而逐渐减小并合为一体，这可能是由不同生活习性的海洋生物造成的。  相似文献   

海底管线维护中底床表层稳定粗化层的构建     

李近元  马小川  阎军 《海洋科学》2018,42(9):10-16

以东方岸外海域为例,计算了极端天气下不同水深条件构建稳定粗化层抛石颗粒的临界粒径;分析了影响粗化层稳定的不同因素,并对人工抛石构建粗化层提出建议。结果显示,在东方岸外30m和60 m水深处,沉积物的中值泥沙粒径至少为30.33 mm和3.99 mm,才能抵御极端浪流的冲刷,且抛石层的厚度应至少为80.9mm和10.8mm,抛石层至少覆盖原始床沙的70%。粗化层的稳定性受颗粒隐蔽暴露效应、砂组分百分比、粗化层颗粒级配、覆盖厚度及覆盖百分比的共同影响,而抛石构建稳定粗化层的实质是对抛石粒径的合理选取及对细粒组分百分比的有效控制。另外,抛石级配的合理选择应受到重视,在施工过程中则需保证覆盖百分数和粗化层的覆盖厚度。粗细混合投放或者分层投放有利于更好地构建稳定粗化层。以上述方法构建稳定粗化层可为海底管道工程设施的维护提供有效支持。  相似文献