In most previous studies of tropospheric tomography, water vapor is assumed to have a homogeneous distribution within each voxel. The parameterization of voxels can mitigate the negative effects of the improper assumption to the tomographic solution. An improved parameterized algorithm is proposed for determining the water vapor distribution by Global Navigation Satellite System (GNSS) tomography. Within a voxel, a generic point is determined via horizontal inverse distance weighted (IDW) interpolation and vertical exponential interpolation from the wet refractivities at the eight surrounding voxel nodes. The parameters involved in exponential and IDW interpolation are dynamically estimated for each tomography by using the refractivity field of the last process. By considering the quasi-exponential behavior of the wet refractivity profile, an optimal algorithm is proposed to discretize the vertical layers of the tomographic model. The improved parameterization algorithm is validated with the observational data collected over a 1-month period from 124 Global Positioning System (GPS) stations of Hunan Province, China. Assessments by GPS, radiosonde, and European Centre for Medium-Range Weather Forecasts (ECMWF) ReAnalysis 5 (ERA5) data, demonstrate that the improved model outperforms the traditional nonparametric model and the parameterized model using trilinear interpolation. In the assessment by GPS data, the improved model performs better than the traditional model and the trilinear parameterized model by 54% and 10%, respectively. Such improvements are 31% and 10% in the validation by radiosonde profiles. In comparison with the ERA5 reanalysis, the improved model yields a minimum overall root mean square (RMS) error of 8.94 mm/km, while those of the traditional and trilinear parametrized models are 10.79 and 9.73 mm/km, respectively. The RMS errors vertically decrease from ~20 mm/km at the bottom to ~5 mm/km at the top layer.

中文翻译：

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使用改进的参数化对流层层析成像技术重建湿折射率场

在对流层层析成像的大多数先前研究中，假定水蒸气在每个体素内具有均匀分布。体素的参数化可以减轻不正确假设对层析成像解决方案的负面影响。提出了一种改进的参数化算法，用于通过全球导航卫星系统（GNSS）层析成像确定水蒸气分布。在体素内，通过水平逆距离加权（IDW）插值和垂直指数插值，根据周围八个体素节点处的湿折射率来确定通用点。通过使用最后一个过程的折射率字段，可以对每个断层扫描动态估计指数和IDW插值所涉及的参数。考虑湿折射率分布的准指数行为，提出了一种优化算法来离散化层析成像模型的垂直层。利用从湖南省124个全球定位系统（GPS）站历时1个月收集的观测数据验证了改进的参数化算法。GPS，无线电探空仪和欧洲中距离天气预报中心（ECMWF）重新分析5（ERA5）数据进行的评估表明，改进后的模型优于传统的非参数模型和使用三线性插值的参数化模型。在GPS数据评估中，改进模型的性能分别比传统模型和三线性参数化模型好54％和10％。通过探空仪剖面图的验证，这种改进分别为31％和10％。与ERA5重新分析相比，改进后的模型产生的最小整体均方根（RMS）误差为8.94 mm / km，而传统和三线性参数化模型的均方根误差分别为10.79和9.73 mm / km。RMS误差从底部的〜20 mm / km垂直减小到顶层的〜5 mm / km。