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31.
32.
SAR(Synthetic Aperture Radar)反演海洋风矢量是当今微波遥感领域非常有意义的前沿课题. 本文首先介绍了星载SAR估算海面风向、风速的基本原理和三种主流反演算法,接着给出反演的流程图以及重要步骤. 然后,以2002年5月7日香港地区ERS-2 SAR海洋图像为例,对经典的SWDA (SAR Wind Direction Algorithm)-谱分析方法加以改进,求得具有180°模糊度的风向,并用香港天文台气象浮标实测数据消除了风向不确定性. 最后,利用CMOD4 GMF(Geophysical Model Function,地球物理模式函数)计算得到海面上10m高的风速. 与气象浮标站实测资料相比,利用ERS-2 SAR图像获取的海面风向、风速的精度均较高. 这一结果表明:如果对SAR预先进行ADC(Analog to Digital Converter)改正以及精确校准,结合改进的SWDA和CMOD4,可以获得高精度的风矢量. 相似文献
33.
基于SMAP卫星雷达资料的海冰密集度反演技术研究 总被引:1,自引:0,他引:1
SMAP是美国于2015年初发射的一颗卫星,搭载了L波段的雷达。它采用圆锥扫描方式,具有固定的入射角、较大的幅宽和千米级的分辨率,在海冰监测方面具有独特的优势。本文利用SMAP卫星雷达资料分别与德国Bremen大学海冰密集度产品和美国国家冰雪数据中心(NSIDC)海冰密集度产品建立3.125 km和25 km匹配数据集,分析了L波段雷达后向散射系数、极化比和归一化极化差与海冰密集度之间相关性,建立基于人工神经网络的海冰密集度反演算法。为了验证SMAP卫星雷达资料反演海冰密集度的精度,本文选择德国Bremen大学和美国冰雪数据中心发布的海冰密集度产品分别与SMAP海冰密集度产品进行对比分析,SMAP海冰密集度与Bremen海冰密集度的偏差为0.07、均方根误差为0.14;与NSIDC海冰密集度的偏差为0.04、均方根误差为0.18,这表明SMAP海冰密集度产品与现有业务化海冰密集度产品具有很好的一致性。 相似文献
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E. Nakakita S. Ikebuchi M. Shiiba T. Takasao 《Stochastic Environmental Research and Risk Assessment (SERRA)》1990,4(2):135-150
A computational method for the determination of rainfall distribution for applications in short term rainfall prediction is presented here. The method is strongly influenced by the experience gained from the observation and analysis of data gathered on a heavy rainfall event in 1986 that occurred during the Baiu Season in Japan. The method is based on the concept that rainfall occurs as an interaction between an instability field, appropriately modeled, and a field of water vapor under the influence of topography. The results from this computational method showed good agreement with the temporal variation in the rainband that moved across the observation field in 1986. Towards determination of the parameters in the computational model, another method for the determination of the rainfield is also developed. This second method determines the rainfall distribution from estimation of the conversion rate of water vapor to liquid water through use of data from a three dimensional scanning radar. The results are consistent with those obtained from the first method. 相似文献
36.
A large sample of summertime data from the McGill Radar Weather Observatory was analyzed to determine the variation with altitude
of the horizontal extent of individual rainshowers. For echoes defined by a reflectivity factor of 39 dBz (equivalent to a
rainfall rate of about 10 mm/h) it was found that the mean area of the total population of echoes decreases linearly with
altitude from approximately 20 km2 at 2 km to 11 km2 at 8 km. Subsets of the total population were investigated, consisting of only the echoes penetrating the altitudes of 6,
7, and 8 km. On the average these relatively tall echoes are much greater in horizontal extent than the total population.
Whereas the sizes of the total population of echoes at any altitude are distributed approximately exponentially in terms of
the square root of area, the sizes of the “survivors” that extend to high altitudes may be described by the gamma distribution
with a mean value decreasing approximately linearly with height above 3 km and a dispersion of 0.55. Some characteristics
are also reported for echoes defined by reflectivities of 31 dBz and 47 dBz. Estimates are given of the fraction of the total
area in a horizontal plane that contains echoes in each of these categories. 相似文献
37.
A large sample of radar reflectivity data from essentially a full summer of operation was analyzed to determine the horizontal
extents and internal structure of rain areas observed at altitude levels from 2 to 10 km. Results are given on the size distributions
of individual cells or patches defined by reflectivity thresholds approximately 4 dBz apart, on the dependence of mean size
on altitude and reflectivity threshold, and on the interior structure of the patches as characterized by the number and sizes
of higher-threshold patches contained in each echo. In a more detailed analysis of internal structure, the data were restricted
to convective echoes in which certain prescribed reflectivities, ranging from about 30 to 50 dBz, were exceeded. It was found
that the dependence of mean quantities, such as patch area, on reflectivity and altitude could be approximately described
by simple functions, but that the scatter of observations about the mean was usually large. 相似文献
38.
39.
Short-term risk forecasts of point precipitation are obtained with COTREC/RainCast, a technique for extrapolation of radar images. The risk forecasts are updated every 5 min for the next 0–2 h. Risk levels are defined for moderate, heavy and extreme precipitation. Warning messages are generated if, at the locations of 23 rain gauges, these risk levels are reached or exceeded. The time-resolved gauge data are used to judge if the warning messages are in time, early or late.Data over a period of 4 months (summer 2002) are used for verification. The largest number of warnings (1790) was obtained for moderate precipitation. About 55% of these warnings were in time, 23% were early and 22% were late. This finding is in a good agreement with the defined risk level for warnings (50%), indicating that the model for calculating the risk factors is reliable. Less warnings in time, and more late warnings were found for heavy and extreme precipitation. Hence, the risk levels need to be lowered for heavy and extreme precipitation, in order to reduce the number of late warnings. 相似文献
40.
Observations were carried out at National Astronomy and Ionospheric Center (NAIC) in Puerto Rico with a dual-frequency (46.8MHz/430MHz) Strato-Tropospheric radar associated with ground-based precipitation and electrostatic field measurements. This experimental set-up is devoted to provide wind measurements and detection of clear air turbulence. During a thunderstorm event, VHF-UHF radar receivers detected wide frequency band radiation emitted by lightning flashes. We present in this paper observations of a specific storm for which lightning radiation and ionized lightning channel were fortuitously and simultaneously detected. A bi-level structure of the lightning flash channel is observed and is consistent with observations obtained previously by other authors with VHF lightning mapper. 相似文献