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Spatial downscaling of radar-derived rainfall field by two-dimensional wavelet transform
Hydrology Research ( IF 2.7 ) Pub Date : 2020-06-01 , DOI: 10.2166/nh.2020.165
Vahid Nourani 1, 2 , Armin Farshbaf 1 , S. Adarsh 3
Affiliation  

Downscaling of rainfall fields, either as images or products of global circulation models, have been the motive of many hydrologists and hydro-meteorologists. The main concern in downscaling is to transform high-resolution properties of the rainfall field to lower resolution without introducing erroneous information. In this paper, rainfall fields obtained from Next Generation Weather Surveillance Radar (NEXRAD) Level III were examined in the wavelet domain which revealed sparsity for wavelet coefficients. The proposed methodology in this work employs a concept named Standardized Rainfall Fluctuation (SRF) to overcome the sparsity of rainfall fields in wavelet domain which also exhibited scaling behaviors in a range of scales. SRFs utilizes such scaling behaviors where upscaled versions of the rainfall fields are downscaled to their actual size, using a two-dimensional discrete wavelet transform, to examine the reproduction of the rainfall fields. Furthermore, model modifications were employed to enhance the accuracy. These modifications include removing the negative values while conserving the mean and applying a non-overlapping kernel to restore high-gradient clusters of rainfall fields. The calculated correlation coefficient, statistical moments, determination coefficient and spatial pattern display a good agreement between the outputs of the downscaling method and the observed rainfall fields.



中文翻译:

二维小波变换的雷达降水场空间缩减

降雨场的缩小,无论是图像还是全球环流模型的产物,都是许多水文学家和水文气象学家的动机。降级的主要考虑是将降雨场的高分辨率属性转换为较低的分辨率,而不会引入错误的信息。本文在小波域中研究了从下一代气象监视雷达(NEXRAD)III级获得的降雨场,揭示了小波系数的稀疏性。在这项工作中提出的方法论采用了一个称为标准化降雨波动(SRF)的概念,以克服小波域降雨场的稀疏性,该稀疏性在小范围内也表现出尺度行为。SRF利用这种缩放行为,将降雨场的放大版本缩小到其实际大小,使用二维离散小波变换来检查降雨场的再现。此外,采用模型修改来提高准确性。这些修改包括在保留平均值的同时除去负值,并应用不重叠的核以还原降雨场的高梯度群集。计算得出的相关系数,统计矩,确定系数和空间模式在缩减方法的输出与观测到的降雨场之间显示出良好的一致性。这些修改包括在保留平均值的同时除去负值,并应用不重叠的核以还原降雨场的高梯度群集。计算得出的相关系数,统计矩,确定系数和空间模式在缩减方法的输出与观测到的降雨场之间显示出良好的一致性。这些修改包括在保留均值的同时删除负值,并应用不重叠的核以还原降雨场的高梯度群集。计算得出的相关系数,统计矩,确定系数和空间模式在缩减方法的输出与观测到的降雨场之间显示出良好的一致性。

更新日期:2020-06-01
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