基于模糊神经网络(FNN)的赤潮预警预测研究   总被引：6，自引：0，他引：6  

王洪礼  葛根  李悦雷 《海洋通报》2006,25(4):36-41

为研究各种理化因子与赤潮藻类浓度间的非线性对应规律和有效预测赤潮藻类浓度,构建了基于BP算法的一个四层模糊神经网络模型。将模糊神经网络(FNN)技术引入赤潮预测研究,并与普通BP网络、RBF网络的结果作比较,结果表明,该模型能够较好地反演出各种理化因子与夜光藻密度的非线性对应变化规律,有更好的预测功能。  相似文献   

Error Calculation in Maritime Delimitation between States with Opposite or Adjacent Coasts     

Milan Horemuz 《Marine Geodesy》1999,22(1):1-17

The sea boundary between two states with opposite or adjacent coasts is defined by the median line between baselines realized on shore lines. As defined in UNCLOS (United Nations Convention on the Law of the Sea), every point of the median line must be equidistant from the nearest points on the baselines from which the breadth of the territorialseas of each ofthe two states is measured. The coordinates of breakpoints of the median line are computed based on known coordinates of baseline points on the shores. What is the precision of computed coordinates? Here we study the error propagation on two reference surfaces: (1) plane and (2) sphere. Moreover, four approaches to breakpoint determination are investigated. Algorithms for computation of the covariance matrix of median line breakpoints both on sphere and plane were developed.  相似文献   

中美洲海域第二模态内孤立波的地震海洋学研究          下载免费PDF全文

范文豪  宋海斌  龚屹  张锟  孙绍箐 《地球物理学报》2021,64(1):195-208

以往利用地震海洋学方法发现的内孤立波大多是第一模态内孤立波,本文利用地震海洋学方法首次在中美洲太平洋沿岸海域发现了第二模态内孤立波群.通过叠前偏移观察该第二模态内孤立波群细结构的变化,发现位于陆坡上的第二模态内孤立波ISW4在大约50 s的采集过程中,出现反射同相轴分叉、合并以及密跃层中心深度变化.利用共偏移距道集叠前...  相似文献   

梅雨锋上短时强降水系统的发展模态   总被引：4，自引：0，他引：4  

张小玲  余蓉  杜牧云 《大气科学》2014,38(4):770-781

利用2010、2011年5～7月我国东部地区梅雨锋盛行期的58次强降水个例,对产生短时强降水的中尺度对流系统回波演变模态及其系统特征进行了统计分析。本文中短时强降水特指小时降水超过30 mm。结果表明,与梅雨锋相伴的短时强降水系统回波演变模态主要为纬向型、经向型、转向型和合并型四类。纬向型、经向型和70%的转向型发展模态中中尺度对流系统（MCS）呈线状,合并型则主要为卵状。纬向型、转向型和合并型MCS以后向传播为主,但它们的生命史、移速和产生强降水持续时间有很大差别:纬向型生命史最长,强降水持续时间比转向型短;三类发展模态中转向型移速最快,生命史较纬向型短,但强降水持续时间最长;合并型移动最慢,生命史最短,强降水持续时间也最短。经向型MCS前向传播为主,移动最快,系统持续史短,约为纬向型的一半,30 mm h-1、50 mm h-1以上强降水持续时间约为转向型的1/3和1/5。纬向型MCS可向东或向南移动,经向型MCS通常向东或向西运动,合并型MCS可往任意方向移动,并且只有该发展模态中MCS会向北运动。虽然转向型MCS带来的短时强降水（尤其50 mm h-1以上）持续时间最长,经向型和合并型MCS产生短时强降水持续时间短,但四类发展模态中MCS的回波强度和回波高度的统计特征无明显区别。推测强降水持续时间可能与MCS的传播关系更加密切:经向型和合并型MCS前向传播占很大比重,生命史和产生的强降水更短;转向型和纬向型MCS的后向传播比重大,尤其转向型中不存在前向传播,对应短时强降水持续时间最长。  相似文献   

非坐标方法确定卫星时间信号的传递时延     

宋金安 《时间频率学报》1995,(1)

在卫星电视授时系统方案中，为确定标准秒信号从发射站经卫星到用户接收站的传播时延值，需要知道收、发地面站及卫星的坐标，所以，在高精度的卫星电视授时系统中，需要建立高精度的同步卫星定位同。本文提出在没有卫星定位同的条件下，用非坐标方法来确定卫星时间信号到用户的传递时延，其授时精度为几μｓ。  相似文献   

Analysis of temporal and spatial characteristics of waves in the Indian Ocean based on ERA-40 wave reanalysis     

《Applied Ocean Research》2017

Based on the 45-year (09/1957-08/2008) European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA-40) wave reanalysis dataset, this study analyzes interannual and interdecadal variabilities and intraseasonal oscillations of sea surface wind speed (WS), wind sea wave height (H^w), swell wave height (H^s) and significant wave height (H_s) in the Roaring Forties and tropical waters of the Indian Ocean, to determine swell propagation characteristics. The results show: (1) monthly variabilities of H^s in the Roaring Forties are in good agreement with those in tropical waters of the Indian Ocean; swell plays a dominant role in mixed waves throughout most of the Indian Ocean; and WS, H^w, H^s, and H_s exhibit a significant increasing trend over the 45-year study period. (2) H^s in the Roaring Forties and tropical waters of the Indian Ocean share a common period of 9.8–10.4 years on an interdecadal scale; and WS and H^s in the Roaring Forties and H^s in the tropical waters of the Indian Ocean share a common period of approximately 8 days (weekly oscillation) on an intraseasonal scale. (3) Swell of the Roaring Forties needs approximately 30 h to fully respond to the wind in this region. Approximately 84 h are required for H^s to propagate from the Roaring Forties to the tropical waters of the south Indian Ocean, while it takes approximately 132–138 h for H^s to propagate from the Roaring Forties to the tropical waters of the north Indian Ocean.  相似文献   

陆面模式中土壤和植被经验参数随机误差的传播研究   总被引：3，自引：1，他引：2  

梁晓  戴永久 《大气科学》2010,34(2):457-470

数据质量问题和模式参数化方案的非完备性是陆面模拟中不确定性的主要来源。本文将高斯误差传播原理 (Gaussian Error Propagation, GEP) 应用于通用陆面模式 (the Common Land Model, CoLM), 研究关键的植被和土壤属性参数随机误差在模式中的传播, 确定由此类误差导致的CoLM模拟的不确定性。结果表明: (1) 基于本研究给定的土壤和植被参数的不确定性, CoLM模拟的表层土壤温度、 土壤湿度和植被蒸散通量 (植冠蒸腾+地表蒸发) 的相对误差分别为0.11%、 34.07%和5.58%; 砂土和稀疏森林上模拟效果最差。土壤参数随机误差对CoLM模拟的影响高于植被参数, 而土壤水文参数 (孔隙率、 饱和基质势、 气孔尺寸分布指数和饱和导水率) 对各模拟量不确定性的贡献率均远大于热力参数 (饱和反照率和热容)。对于本研究涉及的所有模拟变量而言, 最关键的参数均是气孔尺寸分布指数b, 这可能与描述基质势与体积水含量关系的函数有关, 其次重要的是砂土的孔隙度和粘土的饱和导水率。混交森林上的根深分布和苔原上的动力学粗糙度对蒸散通量贡献显著。本身相对误差大的经验参数对CoLM模拟不确定性的贡献不一定多。 (2) 干燥条件下 (表层液态水饱和度小于0.1) 土壤温度的不确定性大; 相变发生时刻附近 (表层土壤温度在0℃附近且表层液态水含量大于0) 土壤湿度不确定性显著; 蒸散通量的不确定性随本身绝对值的增大而增大, 在相对温暖干燥环境中 (表层土壤温度高于280 K且表层液态水饱和度小于0.3) 其不确定性最高。研究证实, GEP能够辨识CoLM中需优先提高观测精度的关键参数和关键参数化过程, 对陆面模拟的参数选定、 不确定性评估和模式完善具有重要意义。  相似文献   

Echo intensity data as a directional antenna for observing processes above sloping ocean bottoms     

Hans van Haren 《Ocean Dynamics》2007,57(2):135-149

Relative ‘echo intensity’ data (dI) from a bottom-mounted four-beam 300 kHz acoustic Doppler current profiler (ADCP) are used to infer propagation of vigorous processes above a continental slope. The 3- to 60-m horizontal beam spread and the 2-Hz sampling allow the distinction of different arrival times t _i , i = 1,..., 4, at different distances in the acoustic beams from sharp changes in dI-content associated with frontal non-linear and turbulent bores or ‘waves’. The changes in dI are partially due to variations in amounts of resuspended material carried by the near-bottom turbulence and partially due to the fast variations in density stratification (‘stratified turbulence’), as inferred from 1-Hz sampled thermistor string data above the ADCP. Such bores are observed to pass the mooring up to 80 m above the bottom, having typical propagation speeds c = 0.15–0.5 m s⁻¹, as determined from dI(t _i ). Particle speeds in the immediate environment of a bore amount to |u|_env=c ± 0.05 m s⁻¹, the equality being a necessary condition for kinematic instability, whilst the maximum particle speeds amount |u|_max = 1.2–2c. The dI-determined directions of up-, down- and alongslope processes are all to within ±10° of the ADCP’s beam-spread averaged current (particle velocity) data.  相似文献   

Impacts of Positional Error on Spatial Regression Analysis: A Case Study of Address Locations in Syracuse, New York   总被引：1，自引：0，他引：1  

Daniel A Griffith  Marco Millones  Matthew Vincent  David L Johnson  Andrew Hunt 《Transactions in GIS》2007,11(5):655-679

Positional error is the error produced by the discrepancy between reference and recorded locations. In urban landscapes, locations typically are obtained from global positioning systems or geocoding software. Although these technologies have improved the locational accuracy of georeferenced data, they are not error free. This error affects results of any spatial statistical analysis performed with a georeferenced dataset. In this paper we discuss the properties of positional error in an address matching exercise and the allocation of point locations to census geography units. We focus on the error's spatial structure, and more particularly on impacts of error propagation in spatial regression analysis. For this purpose we use two geocoding sources, we briefly describe the magnitude and the nature of their discrepancies, and we evaluate the consequences that this type of locational error has on a spatial regression analysis of pediatric blood lead data for Syracuse, NY. Our findings include: (1) the confirmation of the recurrence of spatial clustering in positional error at various geographic resolutions; and, (2) the identification of a noticeable but not shockingly large impact from positional error propagation in spatial auto‐binomial regression analysis results for the dataset analyzed.  相似文献   

1991年3月22日耀斑激波的传播特性   总被引：2，自引：3，他引：2       下载免费PDF全文

刘绍亮  刘四清 《地球物理学报》1996,39(3):289-295

采用ＭＨＤ数值方法研究了１９９１年３月２２日２２：４７ＵＴ日面大耀斑引起的行星际激波传播的几何特性，以及初始驱动时间对传播的影响。得出：１．该激波在黄道面投影是非对称的，最快处偏离耀斑法线向东；２．激波面偏离球面，但随着远离太阳这种偏离减小；３．总能相同时，驱动时间短的激波较强，速度较快；能量变化范围相同时，不同初速比不同驱动时间对激波传播速度影响更大。  相似文献