Dual-wavelength (3.2 and 0.32 cm, i.e., X- and W-radar bands) radar ratio (DWR) measurements in ice clouds and precipitation using Canada's National Research Council Institute for Aerospace Research airborne radar are compared to closely collocated particle microphysical in situ sampling data in order to develop relations between DWR and characteristic hydrometeor size. This study uses the radar and in situ data sets collected during the In-Cloud ICing and Large-drop Experiment (ICICLE) campaign in midlatitude frontal clouds. Since atmospheric particle scattering at X band is predominantly in the Rayleigh regime and the W-band frequency is the highest frequency usually used for hydrometeor remote sensing, the X–W-band combination provides a relatively strong dual-wavelength reflectivity difference. This study considers radar and in situ measurements conducted in relatively homogeneous cloud and precipitation conditions. Measurements show that under these conditions, the difference between the X-band radar reflectivities observed with vertical and horizontal pointing of the radar beam are generally small and often negligible. However, W-band reflectivities at vertical beam pointing are, on average, larger than those for horizontal beam pointing by about 4 dB, which is a non-Rayleigh scattering effect from preferentially oriented non-spherical particles. A horizontal radar beam DWR–mean volume particle size relation, D_v, provides robust estimates of this characteristic size for populations of particles with different habits. Uncertainties of D_v retrievals using DWR are around 0.6 mm when D_v is greater than approximately 1 mm. Size estimates using vertical radar beam DWRs have larger uncertainties due to smaller dual-wavelength signals and stronger influences of hydrometeor habits and orientations at this geometry of beam pointing. Mean relations among different characteristic sizes, which describe the entire particle size distribution (PSD), such as D_v, and other sizes used in various applications (e.g., the mean, effective, and median sizes) are derived, so the results of this study can be used for estimating different PSD characteristic sizes.

中文翻译：

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使用双波长雷达比确定冰水凝物数量

双波长（3.2 和 0.32 厘米，即 X 和 W 雷达波段）使用加拿大国家研究委员会航空航天研究所机载雷达在冰云和降水中测量的雷达比 (DWR) 与紧密并置的粒子微物理原位采样数据进行比较，以建立两者之间的关系DWR 和特征水凝物尺寸。本研究使用在中纬度锋云的云内 ICing 和大落差实验 (ICICLE) 活动期间收集的雷达和原位数据集。由于 X 波段的大气粒子散射主要处于瑞利状态，而 W 波段频率是水气遥感通常使用的最高频率，因此 X-W 波段组合提供了相对较强的双波长反射率差异。本研究考虑了在相对均匀的云和降水条件下进行的雷达和现场测量。测量表明，在这些条件下，通过雷达波束的垂直和水平指向观察到的 X 波段雷达反射率之间的差异通常很小并且通常可以忽略不计。然而，平均而言，垂直光束指向的 W 波段反射率比水平光束指向的反射率大约 4 dB，这是来自优先定向的非球形粒子的非瑞利散射效应。水平雷达波束 DWR-平均体积粒子尺寸关系D _v为具有不同习惯的粒子群提供了对该特征尺寸的稳健估计。当D _v大于约 1  mm时，使用 DWR 检索D _v的不确定性约为 0.6  mm. 使用垂直雷达波束 DWR 的尺寸估计具有较大的不确定性，这是由于较小的双波长信号以及在这种波束指向的几何形状下水凝物习性和方向的影响较大。导出了描述整个粒度分布 (PSD) 的不同特征尺寸之间的平均关系，例如D _v，以及用于各种应用的其他尺寸（例如，平均尺寸、有效尺寸和中值尺寸），所以这个结果研究可用于估计不同的 PSD 特征大小。