Abstract. A method is developed to use both polarimetric and dual-frequency radar measurements to retrieve microphysical properties of falling snow. It is applied to the Ku- and Ka-band measurements of the NASA Dual-polarization, Dual-frequency Doppler Radar (D3R) obtained during the International Collaborative Experiment for PyeongChang Olympic and Paralympics (ICE-POP 2018) field campaign, and incorporates the Atmospheric Radiative Transfer Simulator (ARTS) microwave single scattering property database for oriented particles. The retrieval uses optimal estimation to solve for several parameters that describe the particle size distribution (PSD), relative contribution of pristine, aggregate, and rimed ice species, and the orientation distribution along an entire radial simultaneously. Examination of Jacobian matrices and averaging kernels show that the dual wavelength ratio (DWR) measurements provide information regarding the characteristic particle size, and to a lesser extent, the rime fraction and shape parameter of the size distribution, whereas the polarimetric measurements provide information regarding the mass fraction of pristine particles and their characteristic size and orientation distribution. Thus, by combining the dual-frequency and polarimetric measurements, some ambiguities can be resolved that should allow a better determination of the PSD and bulk microphysical properties (e.g., snowfall rate) than can be retrieved from single-frequency polarimetric measurements or dual-frequency, single-polarization measurements. The D3R ICE-POP retrievals were validated using Precipitation Imaging Package (PIP) and Pluvio weighing gauge measurements taken nearby at the May Hills ground site. The PIP measures the snow PSD directly, and its measurements can be used to derived the snowfall rate (volumetric and water equivalent), mean volume-weighted particle size, and effective density, as well as particle aspect ratio and orientation. Four retrieval experiments were performed to evaluate the utility of different measurement combinations: Ku-only, DWR-only, Ku-pol, and All-obs. In terms of correlation, the volumetric snowfall rate (r = 0.95) and snow water equivalent rate (r = 0.92) were best retrieved by the Ku-pol method, while the DWR-only method had the lowest magnitude bias for these parameters (−31 % and −8 %, respectively). The methods that incorporated DWR also had the best correlation to particle size (r = 0.74 and r = 0.71 for DWR-only and All-obs, respectively), although none of the methods retrieved density particularly well (r = 0.43 for All-obs). The ability of the measurements to retrieve mean aspect ratio was also inconclusive, although the polarimetric methods (Ku-pol and All-obs) had reduced biases and MAE relative to the Ku-only and DWR-only methods. The significant biases in particle size and snowfall rate appeared to be related to biases in the measured DWR, emphasizing the need for accurate DWR measurements and frequent calibration in future D3R deployments.

中文翻译：

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ICE-POP 2018 期间 NASA D3R 雷达的雪微物理检索

摘要。开发了一种方法来使用极化和双频雷达测量来检索下雪的微物理特性。它应用于平昌奥运会和残奥会国际合作实验 (ICE-POP 2018) 现场活动期间获得的 NASA 双极化、双频多普勒雷达 (D3R) 的 Ku 和 Ka 波段测量，并结合了定向粒子的大气辐射传递模拟器 (ARTS) 微波单散射属性数据库。检索使用最优估计来求解几个参数，这些参数描述了粒度分布 (PSD)、原始冰、聚集冰和边缘冰种类的相对贡献，以及沿整个径向的方向分布。对雅可比矩阵和平均核的检查表明，双波长比 (DWR) 测量提供了关于特征粒径的信息，并在较小程度上提供了粒径分布的雾化分数和形状参数，而偏振测量提供了关于粒径分布的信息。原始颗粒的质量分数及其特征尺寸和取向分布。因此，通过结合双频和极化测量，可以解决一些模糊问题，从而可以更好地确定 PSD 和体微物理特性（而极化测量提供有关原始颗粒的质量分数及其特征尺寸和取向分布的信息。因此，通过结合双频和极化测量，可以解决一些模糊问题，从而可以更好地确定 PSD 和体微物理特性（而极化测量提供有关原始颗粒的质量分数及其特征尺寸和取向分布的信息。因此，通过结合双频和极化测量，可以解决一些模糊问题，从而可以更好地确定 PSD 和体微物理特性（例如，降雪率）可以从单频极化测量或双频、单极化测量中恢复。使用降水成像包 (PIP) 和在 May Hills 地面站点附近进行的 Pluvio 称重测量来验证 D3R ICE-POP 检索。PIP 直接测量雪 PSD，其测量值可用于推导出降雪率（体积和水当量）、平均体积加权粒度和有效密度，以及颗粒纵横比和方向。进行了四个检索实验以评估不同测量组合的效用：仅 Ku、仅 DWR、Ku-pol 和 All-obs。在相关性方面，体积降雪率（r  = 0.95）和雪水当量率（r  = 0.92) 最好通过 Ku-pol 方法检索，而仅 DWR 方法对这些参数具有最低的幅度偏差（分别为 -31% 和 -8%）。包含 DWR 的方法也与颗粒大小有最好的相关性（ 对于 DWR-only 和 All-obs 分别为r  = 0.74 和r = 0.71），尽管没有一种方法能特别好地检索密度（r = 0.43 对于所有观察者）。尽管极化方法（Ku-pol 和 All-obs）相对于 Ku-only 和 DWR-only 方法减少了偏差和 MAE，但测量检索平均纵横比的能力也没有定论。颗粒大小和降雪率的显着偏差似乎与测得的 DWR 的偏差有关，强调了在未来的 D3R 部署中需要进​​行准确的 DWR 测量和频繁校准。