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1.
针对电离层总电子含量(TEC)数据非线性、非平稳的特点,在自回归移动平均(ARMA)模型的基础上,结合经验小波变换(EWT),提出一种组合的短期电离层预测方法。采用IGS提供的电离层TEC格网数据进行实验,通过对比分析可知,相较于单一ARMA模型,本文组合模型在太阳活动低年和太阳活动高年5 d内的平均相对精度分别提高4.8%和2.8%,前1 d内组合模型的平均相对精度分别提高7%和6.1%。  相似文献   
2.
基于15 d的精密卫星钟差数据,从不同角度全面分析6种常用钟差预报模型(LP模型、QP模型、GM模型、SA模型、ARIMA模型、KF模型)基于钟差一次差分预报原理的预报效果,得到以下结论:1)采用钟差一次差分预报原理,可以提高LP模型、SA模型、GM模型及KF模型对于GPS卫星钟差的3 h预报精度,提高QP模型和ARIMA模型对于ⅡF Rb钟的3 h预报精度,提高LP模型和GM模型在6 h和12 h预报中的精度,提高ARIMA模型在6 h、12 h和24 h预报中的精度;2)基于钟差一次差分预报原理的预报结果与卫星及其星载钟类型有关,对于GPS BLOCK ⅡF Rb钟,该预报原理可以提高6种模型的短期预报精度,特别是对GM模型、LP模型和ARIMA模型预报效果的改善最为显著;3)对于3 h和6 h的预报,采用钟差一次差分预报原理的LP模型(DLP模型)对应的RMS值都最小,即DLP模型的预报精度最高,说明钟差一次差分数据更适合一次多项式模型的短期预报。  相似文献   
3.
随着黑河流域时空数据的快速增长,已有的黑河信息系统在共享效率、数据分析及平台架构等方面存在缺陷,已无法满足现实的需要。本研究针对目前平台的缺陷重新设计新版数字黑河信息系统(NDHRIS)的整体框架,从观测、数据及模型三个角度实现新版数字黑河信息系统的新功能。首先从基础设施、服务及应用三个层面介绍系统整体设计,其次详细阐述系统实现的关键技术及功能改进,最后,讨论了该系统仍然存在的问题及未来发展方向。目前该系统已业务化运行,数据量超过5 T,共1 058条元数据,向大约100个研究所和50个项目提供了大约8 TB数据集和5 000个数据服务,有效提升了黑河流域科学数据的共享效率,支撑全球寒区监测计划的实施。  相似文献   
4.
四川省青川县滑坡灾害群发,点多面广,区域滑坡灾害预警是有效防灾减灾的重要手段,预警模型是成功预警的核心。由于研究区滑坡诱发机理复杂、调查监测大数据及分析方法不足等原因,传统区域地质灾害预警模型存在预警精度有限、精细化不足等问题。文章在青川县地质灾害调查监测和降水监测成果集成整理与数据清洗基础上,构建了青川县区域滑坡灾害训练样本集,样本集包括地质环境、降雨等27个输入特征属性和1个输出特征属性,涵盖了青川县近9年(2010—2018年)全部样本,数量达1 826个(其中,正样本613个,负样本1 213个)。基于逻辑回归算法,对样本集进行5折交叉验证学习训练,采用贝叶斯优化算法进行模型优化,采用精确度、ROC曲线和AUC值等指标校验模型准确度和模型泛化能力。其中,ROC曲线也称为“受试者工作特征”曲线;AUC值表示ROC曲线下的面积。校验结果显示,基于逻辑回归算法的模型训练结果准确率和泛化能力均较好(准确率94.3%,AUC为0.980)。开展区域滑坡实际预警时,按训练样本特征属性格式,输入研究区各预警单元27个特征属性,调用预先学习训练好的模型,输出滑坡灾害发生概率,根据输出概率分段确定滑坡灾害预警等级。当输出概率P≥40%且P<60%时,发布黄色预警;当输出概率P≥60%且P<80%时,发布橙色预警;当输出概率P≥80%时,发布红色预警。  相似文献   
5.
Field measurement and modelling of soil erosion provides insights into landscape systems as well as the potential for enhanced landscape management. There are a number of field and numerical methods by which soil erosion and deposition can be quantified. Here we examine the capability of the SIBERIA landscape evolution model to quantify short-term erosion and deposition on a well-managed cattle grazing landscape on the east coast of Australia. The model is calibrated by two methods (1) a geomorphological approach using a site digital elevation model (DEM) and soil data and (2) a laboratory-scale flume. The two calibration processes resulted in similar model input parameters and estimated erosion rates of 3.1 t ha−1 year−1 and 4.4 t ha−1 year−1, respectively. These were found to closely match erosion rates estimated using the environmental tracer 137Cs (2.7–4.8 t ha−1 year−1). However, erosion and deposition estimated at individual points along the hillslope was not well correlated with 137Cs at the same position due to the temporal averaging of the model and microtopography. Sensitivity analysis showed the model was more sensitive to parameterisation than sub-DEM-scale topography. This places confidence in the model's ability to estimate erosion and deposition across an entire hillslope and catchment on decadal time scales. We also highlight the robustness and flexibility of the calibration methods.  相似文献   
6.
Systematic variations in atmospheric heat exchange, surface residence time, and groundwater influx across montane stream networks commonly produce an increasing stream temperature trend with decreasing elevation. However, complex stream temperature profiles that differ from this common longitudinal trend also exist, suggesting that stream temperatures may be influenced by complex interactions among hydrologic and atmospheric processes. Lakes within stream networks form one potential source of temperature profile complexity due to the spatially variable contribution of lake-sourced water to stream flow. We investigated temperature profile complexity in a multi-season stream temperature dataset collected across a montane stream network containing many alpine lakes. This investigation was performed by making comparisons between multiple statistical models that used different combinations of stream and lake characteristics to represent specific hypotheses for the controls on stream temperature. The compared models included a set of models which used a topographically derived estimate of the hydrologic influence of lakes to separate and quantify the effects of stream elevation and lake source-water contributions to longitudinal stream temperature patterns. This source-water mixing model provided a parsimonious explanation for complex stream-network temperature patterns in the summer and autumn, and this approach may be further applicable to other systems where stream temperatures are influenced by multiple water sources. Simpler models that discounted lake effects were more optimal during the winter and spring, suggesting that complex patterns in stream temperature profiles may emerge and subside temporally, across seasons, in response to diversity of water temperatures from different sources.  相似文献   
7.
基于2018年12月至2020年3月喀左、沈阳、辽阳、满洲里4个国家级地面气象站人工冻土器与测温式冻土自动观测仪观测的资料,对人工冻土观测获得的冻点与测温式冻土自动观测仪获得的相应深度的温度进行对比分析。结果表明:人工冻土器获取的冻点对应的土壤温度与0℃总体一致,又不完全重合;0—35 cm深度范围,冻点对应的温度变化范围为-2~6℃,呈现跳跃性变化。35 cm以下深度范围,冻土冻点对应的温度变化范围为-0.5~1.0℃;融化过程冻点对应的平均温度高于冻结过程冻点对应的平均温度。从完全融化时间上来看,人工冻土器观测到的完全融化时间晚于测温式冻土仪0℃线完全消失的时间。人工冻土观测的实质是获得土壤温度0℃点所在位置。灌注不同台站水的冻土器内管在相同的温度环境下,冻结与融化状态无明显区别;人工冻土器内管冻结过程是温度和持续时间双重作用的结果,深层土壤温度变化缓慢,使得内管中的水冻结和融化需要的时间长。另外,作为接触式测温设备,减小外因产生的时滞是提高其灵敏度的重要环节,建议测温式冻土仪的外管壁使用温度滞后效应更小的金属外管。  相似文献   
8.
现如今,新冠肺炎(COVID-19)严重威胁着世界各国人民的生命健康.许多流行病学模型已经被用于为政策制定者和世界卫生组织提供决策参考.为了更加深刻的理解疫情趋势的变化特征,许多参数优化算法被用于反演模型参数.本文提议使用结合了高斯-牛顿法和梯度下降法的Levenberg-Marquardt(LMA)算法来优化模型参数.使用四个病例数相对较多的国家来验证这一算法的优势:相较于传统流行病学模型模拟曲线过早过快的到达峰值,应用 LMA 的 Statistical-SIR(Statistical-Susceptible-Infected-Recovered)模型可以更好地拟合实际疫情曲线.  相似文献   
9.
We introduce the freely available web-based Water in an Agricultural Landscape—NUčice Database (WALNUD) dataset that includes both hydrological and meteorological records at the Nučice experimental catchment (0.53 km2), which is representative of an intensively farmed landscape in the Czech Republic. The Nučice experimental catchment was established in 2011 for the observation of rainfall–runoff processes, soil erosion processes, and water balance of a cultivated landscape. The average altitude is 401 m a.s.l., the mean land slope is 3.9%, and the climate is humid continental (mean annual temperature 7.9°C, annual precipitation 630 mm). The catchment is drained by an artificially straightened stream and consists of three fields covering over 95% of the area which are managed by two different farmers. The typical crops are winter wheat, rapeseed, and alfalfa. The installed equipment includes a standard meteorological station, several rain gauges distributed across the basin, and a flume with an H-type facing that is used to monitor stream discharge, water turbidity, and basic water quality indicators. Additionally, the groundwater level and soil water content at various depths near the stream are recorded. Recently, large-scale soil moisture monitoring efforts have been introduced with the installation of two cosmic-ray neutron sensors for soil moisture monitoring. The datasets consist of observed variables (e.g. measured precipitation, air temperature, stream discharge, and soil moisture) and are available online for public use. The cross-seasonal, open access datasets at this small-scale agricultural catchment will benefit not only hydrologists but also local farmers.  相似文献   
10.
The drought of summer 2018, which affected much of Northern Europe, resulted in low river flows, biodiversity loss and threats to water supplies. In some regions, like the Scottish Highlands, the summer drought followed two consecutive, anomalously dry, winter periods. Here, we examine how the drought, and its antecedent conditions, affected soil moisture, groundwater storage, and low flows in the Bruntland Burn; a sub-catchment of the Girnock Burn long-term observatory in the Scottish Cairngorm Mountains. Fifty years of rainfall-runoff observations and long-term modelling studies in the Girnock provided unique contextualisation of this extreme event in relation to more usual summer storage dynamics. Whilst summer precipitation in 2018 was only 63% of the long-term mean, soil moisture storage across much of the catchment were less than half of their summer average and seasonal groundwater levels were 0.5 m lower than normal. Hydrometric and isotopic observations showed that ~100 mm of river flows during the summer (May-Sept) were sustained almost entirely by groundwater drainage, representing ~30% of evapotranspiration that occurred over the same period. A key reason that the summer drought was so severe was because the preceding two winters were also dry and failed to adequately replenish catchment soil moisture and groundwater stores. As a result, the drought had the biggest catchment storage deficits for over a decade, and likely since 1975–1976. Despite this, recovery was rapid in autumn/winter 2018, with soil and groundwater stores returning to normal winter values, along with stream flows. The study emphasizes how long-term data from experimental sites are key to understanding the non-linear flux-storage interactions in catchments and the “memory effects” that govern the evolution of, and recovery from, droughts. This is invaluable both in terms of (a) giving insights into hydrological behaviours that will become more common water resource management problems in the future under climate change and (b) providing extreme data to challenge hydrological models.  相似文献   
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