共查询到20条相似文献，搜索用时 31 毫秒
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This study aims to present an encouraging example of prediction of super cyclone Gonu over the northern Indian Ocean in 2007. A series of experiments are conducted using the advanced Weather Research and Forecasting model with three-dimensional variational method to assimilate GPS RO refractivity from FORMOSAT-3/COSMIC (hereafter referred as GPS) and radiosonde sounding (GTS) to highlight the relative impact of GPS RO data on model prediction. Significant differences in cyclone track and intensity prediction are exhibited in various experiments with and without cyclic assimilations. Both cold-start (non-cyclic) and hot-start (cyclic) runs with GPS RO data exhibit improvement on later track prediction compared to the control run without data assimilation. GPS experiment outperforms other experiments including GTS in track prediction with the smallest cross-track error. Sensitivity tests were also conducted to identify which GPS RO sounding gives more impact on track prediction. We found that the sounding closest to the cyclone exhibits the largest contribution to track prediction. Assimilation of the RO soundings in the vicinity of Gonu cyclone appears to modify the environmental conditions that result in a later development of a couplet of high and low pressure, leading to a positive impact on track prediction. Sensitivity experiments indicate that the initial information retrieved by GPS data at upper levels that produce colder temperature increments indeed contributes more improvement to track prediction. 相似文献
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A new stability index based on atmospheric refractivity at ~500 hPa level and surface measurements of temperature, pressure
and humidity is formulated. The new index named here as refractivity based lifted index (RLI) is designed to give similar
results as traditionally used lifted index derived from radiosonde profiles of temperature, pressure and humidity. The formulation
of the stability index and its comparison with the traditional temperature profile based lifted index (LI) is discussed. The
index is tested on COSMIC radio occultation derived refractivity profiles over Indian region. The forecast potential of the
new index for rainfall on 2°×2° latitude–longitude spatial scale with lead time of 3–24 hours indicate that the refractivity
based lifted index works better than the traditional temperature based lifted index for the Indian monsoon region. Decreasing
values of RLI tend to give increasing rainfall probabilities. 相似文献
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鉴于现有研究对GPS-IR技术的反射波接收、低高度角信噪比观测值的使用、信噪比残差的形态等机理还未阐释清楚,且几乎是通过实验进行解释,因此,从理论和实验2个方面对GPS-IR技术机理进行分析。理论和实验证明:GPS卫星发射的右旋圆极化波经一次反射后部分转换为左旋圆极化波,转换比例随着高度角和介电常数增大而变大,当右旋圆极化波垂直入射到理想导体表面时,经一次反射才能全部转换为左旋圆极化波;同时在测量型GPS接收机安装有抑径板的情况下,因衍射现象的存在,测量型GPS接收机天线仍能接收反射波中的右旋圆极化波。当高度角越小或介电常数越大时,GPS入射波中的垂直极化波和平行极化波的能量透射到反射物中就越少,其反射波的强度就越大,信噪比受反射波影响就越严重,且能够接收的右旋圆极化波较多,因此GPS-IR使用的是低高度角(如30°以下)的信噪比观测值。当高度角变化范围较小时,信噪比残差序列呈近似"余弦曲线"形态,从而建立了基于信噪比残差的反演模型。 相似文献
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利用成都地基全球定位系统(GPS)观测网2004年7~9月的观测数据,结合自动气象站获得的气象资料计算出GPS遥感的可降水量(PWV).与气象探空站观测资料算出的可降水量进行对比,确定出本次GPS遥感可降水量的精度为3.09 mm.并对成都、郫县夏季PWV的日循环特征进行了合成分析.结果表明:PWV呈明显的日循环,最小值出现在8:00(北京时间),成都和郫县分别为40.5 mm和35.0 mm;最大值出现在17:00左右,成都和郫县分别为43.5 mm和38.0 mm.白天PWV的变化较大,夜间相对稳定,日变幅为3 mm.在盛夏静稳型天气下,成都地区的PWV日循环特征与地面气温基本一致,皆受太阳辐射日变化的控制.降水日变化的一个显著特点是降水主要发生在夜间,当PWV在下午达到最大之后,主降水阶段开始,使PWV明显减少,同时使地面空气比湿迅速增大;当PWV下降到一个稳定状态后,主降水过程随之结束.大气水汽总量的积累和释放与地面降水有较好的对应关系,PWV的持续性递增和持续性递减预示着降水的开始和结束. 相似文献
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The available research on technology mechanism of reflected wave reception, the use of the SNR observations of low elevating angle and the form of SNR residuals for GPS-IR is not clear enough, and they are almost interpreted by experiments. This paper analyzed the GPS-IR technology mechanism from the aspects of theories and experiments. The right hand circular polarized wave transmitted by GPS satellite is partly converted into left hand circular polarized wave after one reflection, and the conversion ratio increases with the increase of satellite elevating angle and dielectric constant. When the right hand circular polarized wave is perpendicular to the surface of the perfect conductor, it can be all converted into left hand circular polarized wave after a reflection; At the same time, in the case of the measuring GPS receiver equipped with the baffle plate, because of the diffraction phenomenon, the antenna of the measuring GPS receiver can still receive the right hand circular polarized wave in the reflected signal. When the elevating angle is smaller or the dielectric constant of the reflector is larger, the less GPS incident wave energy of vertically polarized wave and parallel polarized wave is transmitted to the reflector. The more intense the reflected wave is, the worse the SNR is affected by the reflected wave, and there are more right hand circular polarized waves that can be received. Therefore, the GPS-IR uses the SNR observations of low elevating angle (such as under 30°). When the elevating angle changes and the range is smaller, the SNR residuals sequence is approximately "cosine curve", and thus, an inversion model based on SNR residuals is established. 相似文献
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AVO技术在油气勘探中已经得到广泛应用,但是在应用Zoeppritz方程的线性近似方程时,通常是直接应用入射角代替平均角进行参数计算,这样做会给反演工作带来误差。基于入射角的AVO近似方程将反射系数表示为入射角的函数,可以解决常规计算中存在的误差。过程如下:首先,由基于入射角的AVO近似方程推导得到基于入射角的弹性阻抗方程,将其标准化以实现不同角度的弹性阻抗间量纲的统一,并通过经典的AVO模型验证其准确性;然后,建立基于新方程的弹性阻抗反演方法,对Marmousi2模型进行反演,与常规方法反演结果进行对比,结果表明,新方法得到的结果更加准确;最后,利用某实际工区数据进行反演,得到的结果与实际测井资料匹配效果很好,证明了该方法有很强的实用性。 相似文献
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Characterization of the atmospheric boundary layer from radiosonde observations along eastern end of monsoon trough of India 总被引：1，自引：0，他引：1
In this paper, a comparison of two methods for the calculation of the height of atmospheric boundary layer (ABL), using balloon-borne GPS radiosonde data is presented. ABL has been characterized using vertical profiles of meteorological parameter. The gradient of virtual potential temperature (?? v ) profile for the determination of mixed layer heights (MLH) and the mean value of turbulent flow depth (TFD) obtained from the vertical profile of Bulk Richardson Number (R i B ) have been used in this study. One-year data have been used for the study. There is large seasonal variability in MLH with a peak in the summer and winter whereas the TFD remained steady throughout the year. Results from the present study indicate that the magnitudes of TFD are often larger than the MLH. 相似文献
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Investigating 2-D MT inversion codes using real field data 总被引：1，自引：0，他引：1
Reza Ghaedrahmati Ali Moradzadeh Nader Fathianpour Seong Kon Lee 《Arabian Journal of Geosciences》2014,7(6):2315-2328
There are currently a significant number of two-dimensional (2-D) and three-dimensional (3-D) inversion codes available for magnetotelluric (MT) data. Through various 2-D inversion algorithms suggested so far, the classical Occam's inversion, the data space Occam's inversion, the nonlinear conjugate gradient (NLCG) method, and the Gauss–Newton (GN) method are fundamental driving methods to find optimum earth models, and OCCAM, DASOCC, NLCG, and MT2DInvMatlab are possible candidates one can find in the public domain that implement these algorithms for 2-D MT inversions, respectively. In this study, we investigate the pros and cons (strength and weakness) of these codes to help one use them efficiently in practical works and, as an introductory guide, further develop (sophisticate or extend) them, especially for the 3-D case. To achieve this goal, we applied each one of the four aforementioned codes on a profile of real MT field dataset. Then, further investigations have been done by performing several inversion tests to see how each code can find the appropriate model to reconstruct the subsurface resistivity structure. Numerical experiments show that the two parameters, regularization and target misfit, in addition to the main criteria of inversion (such as the forward and the sensitivities calculation method, and the type of inversion algorithm), are very important to produce the expected model in inversion. The regularization parameter that acts to trade off between model norm and data misfit can affect the inversion process in terms of both the computational efficiency and the accuracy of the obtained model. Also, lack of insufficient precision to choose the target misfit can lead the inversion to produce and reach an incorrect model. 相似文献
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地面GPS探测大气的最新进展 总被引：5，自引：0，他引：5
综述了利用地面ＧＰＳ站探测大气的技术，包括基本原理，方法，应用，最新进展和结果的介绍以及存在于该技术的误差源的讨论。从地面ＧＰＳ站的观测和表面气象参数可得出天顶湿延迟的估计，再由它和可降水汽量之间的转换关系就可得出ＰＷＶ估计。这种方法求得的ＰＷＶ时间序列不仅能提高天气预报的准确度而且有助于气候变化的研究和数值天气预报模型的改进，这就是新兴学科ＧＰＳ气象学形成的基础。 相似文献
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基于6S模型的MODIS影像逐像元大气校正及其应用 总被引：1，自引：0，他引：1
以获取地物真实反射率为目的,介绍了逐像元大气校正的方法。应用6S模型逐像元综合考虑太阳天顶角、传感器天顶角、相对方位角、大气气溶胶厚度、观测波段以及地表海拔这6个参数,生成查找表,统计分析各参数关于反射率的敏感度;并与以往单一参数校正的方法比较了校正的效果。结果表明,逐像元大气校正算法更加接近地物的真实反射率。利用MODIS地表反射率产品对大气校正的结果进行验证,单一参数、逐像元大气校正的相对误差分别控制在26.9%和12.7%以内;在以植被指数(NDVI)为例的后续遥感定量化反演过程中,逐像元比单一参数大气校正方法计算的NDVI平均高出14.4%。 相似文献
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RTK测量有着实时、快捷、全天候等优点,在测量各领域得到广泛应用。本文通过RTK技术在煤田地震勘探方面的实践运用,对其作业方法、作业组织及成果精度作了初步研究。RTK测量的实质是将WGS84坐标系上的高精度三维成果以一定的转换参数,通过实时数据链进行计算转换,最终得到国家或工程独立坐标系的成果,本文亦对其转换参数的求取作了初步探讨。 相似文献
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针对塔河油田3区石炭系卡拉沙依组地震数据很难识别薄砂体的问题,对比分析了采用地震资料提频处理、分频处理、储层高分辨率敏感参数反演等不同手段得到的储层预测结果,筛选出高分辨率储层敏感参数反演作为卡拉沙依组砂泥岩段储层主要预测手段。通过探讨砂泥岩对声波时差的响应,以及对比分析自然电位、自然伽马以及补偿中子孔隙度与声波时差的关系,确定自然电位与声波时差的相关性最好,由此选取自然电位作为最佳电性敏感参数参与高分辨率敏感参数反演预测。从井点、剖面、平面等方面检验和评价高分辨率储层预测成果,结果表明其反演预测效果较好,符合塔河油田3区石炭系的储层预测要求,实现了对石炭系主力砂体空间展布的解释与描述,建立了塔河油田3区石炭系卡拉沙依组储层模型。 相似文献
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建立了波浪、底部离岸流、泥沙运动和沙滩剖面演变耦合数学模型,模拟了实验室中波浪作用下沙坝剖面的形成过程,讨论了各个物理参数对剖面上的水动力和地形变化的影响。通过参数率定,较好地复演了不规则波作用下沙滩地形由均匀斜坡向沙坝剖面的演变,波高、底部离岸流、输沙率和剖面演变的计算结果与实测数据吻合良好。采用数值实验和误差分析方法,讨论了破碎波水滚倾角、泥沙扩散系数和床面休止角等物理参数对计算结果的影响。研究表明,所建立的模型能较好地描述波浪作用下沙坝剖面形成过程中的重要物理机制。 相似文献
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岩体结构面粗糙度系数是快速估算结构面峰值抗剪强度的重要参数。但是结构面轮廓曲线复杂,单一统计参数无法量化表征粗糙度。为解决这一问题,收集了112条结构面轮廓曲线起伏角、起伏度、迹线长度3方面的8项统计参数,利用随机森林回归模型交叉验证的方法评估统计参数的重要性。结果表明：最大起伏度、起伏高度标准偏差、平均起伏角、起伏角标准差、平均相对起伏度及粗糙度剖面指数等6项统计参数重要性占比达到93.2%,且回归拟合系数趋于平稳,基于重要性评估结果建立最优超参数决策树数目(ntree)为400、参与节点分割的数目(mtry)为2的随机森林回归模型,模型预测结果拟合优度高达98.1%。与基于坡度均方根、结构函数及粗糙度剖面指数等传统线性回归结果对比,随机森林回归模型结果精度更高,误差更小,拟合优度提高6%以上,表明随机森林回归模型更适用于结构面粗糙度反演。 相似文献
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受冰-水间相变影响, 冻融期内土壤水、热传输过程变得复杂, 研究气态水分布特征与运移规律, 可为厘清冻融过程中沙地包气带水文循环机理提供关键信息。通过在毛乌素沙地建立原位监测点, 并利用修改后的Hydrus-1D冻融程序建立包气带水-汽-冰-热耦合数值模型, 对冻融期包气带气态水迁移过程展开研究。结果表明: 模拟与实测土壤水分及温度变化拟合较好, 证实所建立的模型具有良好的精度以及适用性; 对比典型未冻结、初始冻结、向下冻结以及融化时段结果可知, 冻融过程会改变剖面土壤水分、含冰量以及水汽密度分布, 其中水汽密度变化与温度联系紧密; 冻结后, 由温度梯度驱动的非等温气态水通量在总水分通量中的占比超过90%, 表明气态水占据主导地位, 其运移过程对于剖面土壤水分分布以及高含水量带出现有重要影响。 相似文献
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分析探讨了锚索桩设计计算的几个力学问题及有关概念。传统上对于桩身嵌入段的计算,须根据桩身与桩周岩土的相对刚度划分为刚性桩和弹性桩两种不同的计算模型,并各自对应不同的算法及计算公式,通过对两种模型计算式的数学极限分析表明,刚性桩模型算式仅为弹性桩计算法中将嵌入段的桩身刚度取很大值下的特例,两种模型算法在力学本质上是统一的。由锚索桩嵌入段分别按弹、刚性桩模型算式的位移、转角的对比分析可知,基于弹性桩模型计算出的锚索受力大于按刚性桩模型,以弹性桩模型进行锚索设计偏于安全,而嵌入段的换算长度取1.3（“m法”）或0.8（“常数法”）,从工程设计角度方可作为刚/弹性桩模型的划分判据,此时两种模型的最大位移或转角差别才小于5 %。桩上锚索倾角的力学效应除矢量分解作用影响水平锚拉力大小外,更重要的是将影响锚拉点处的水平约束刚度,进而改变锚索桩超静定结构的受力分担,因此锚索最优倾角的选取可使较好地控制桩身位移且降低锚索初拉力得以兼顾。力图令桩身正负弯矩峰值大致相等的所谓“平衡设计原则”实际上具有较强条件性,须依赖于锚索既要初拉力合适又能在正常工作状态下具备足够大的锚拉力。 相似文献
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针对混凝土质量检测的特点,采用弯曲射线进行超声层析成像。首先建立波速分布的网格模型,并引入最短路径法进行射线追踪,然后采用联合迭代重建技术（SIRT）反演成像。为使算法适应弯曲射线,对SIRT的计算步骤进行调整,增加外层迭代,以便对修正后的路径进行下一轮反演;为提高反演精度,根据射线传播距离、幅度衰减、频率突变等信息建立和调整信号可信度系数,并依据该系数在求取网格慢度修正值时进行加权平均;为缩短计算时间,动态调整网格节点个数,并进行双向最短路径追踪。经过数值模拟及对混凝土基桩的实测,证明该方法在计算准确性和精度上有明显改进,计算速度也可以满足工程应用的需要。 相似文献