Tropospheric water vapor imaging by combination of ground-based and spaceborne GNSS sounding data
Tropospheric water vapor imaging by combination of ground-based and spaceborne GNSS sounding data
复制标题
DOI：
10.1029/2001jd900230
复制
发表时间：
2001-11
影响因子：
--
通讯作者：
U. Foelsche;G. Kirchengast
中科院分区：
文献类型：
--
作者：
U. Foelsche;G. Kirchengast
全球导航卫星系统（GNSS）包括美国的GPS系统（全球定位系统），俄罗斯的GLONASS系统，以及未来可能的欧洲伽利略系统。最近，在全球定位系统卫星与地面全球定位系统接收器之间的无线电链路中，已经证明了基于全球导航卫星系统的相位延迟测量在准确估计垂直和倾斜路径综合水汽方面的潜力。另一方面，通过全球定位系统/气象学实验证明，基于全球导航卫星系统的无线电掩星可提供具有高垂直分辨率的温度和湿度等大气变量的精确近垂直剖面图。当来自低地球轨道的星载接收器的掩星剖面与来自共址接收器网络的地基全球导航卫星系统数据相结合时，大气水汽的高度分辨成像变得可行。我们开发了一个二维的，高度分辨断层成像技术贝叶斯方法的最佳组合的信息来自不同的来源。使用模拟的GNSS为基础的水汽测量从低地球轨道和地面，我们显示了代表性的结果来自简单的合成的水汽活动领域，以及从一个现实的水汽活动领域的基础上，欧洲中期天气预报中心（ECMWF）分析。对于位于极向40°的情况，我们发现了一个新的简单映射函数，在我们的正演模式方案中表现最好，其中唯一的自由参数是对流层中的气候尺度高度，其确切值并不重要。映射函数利用在表面上方的前两个标尺高度内的直线射线路径长度与由这前两个标尺高度限定的“有效高度”之间的比率。我们发现我们的技术能够重建大气特征，如信风反演顶部附近的水汽最大值。将水汽廓线测量的积分调整为水平平均的地面垂直积分水汽数据有效地减轻了前一数据中的潜在偏差。在绝对湿度高的地区精度最好，但在芬兰等干燥地区，仍然可以获得有用的二维信息。因此，它是有吸引力的应用开发的技术在下一个步骤的真实的数据。
The Global Navigation Satellite System (GNSS) comprises the U.S. system GPS (Global Positioning System), its Russian pendant GLONASS, and presumably, in the future, the European system Galileo. The potential of GNSS-based phase delay measurements for accurately estimating vertically and slant-path-integrated water vapor has been demonstrated recently for radio links between GPS satellites and ground-based GPS receivers. GNSS-based radio occultation, on the other hand, has been demonstrated via the GPS/Meteorology experiment to deliver accurate near-vertical profiles of atmospheric variables such as temperature and humidity with high vertical resolution. Height-resolving imaging of atmospheric water vapor becomes feasible when occultation profiles from spaceborne receivers in Low Earth Orbits (LEO) are combined with ground-based GNSS data from a colocated receiver network. We developed a two-dimensional, height-resolving tomographic imaging technique following the Bayesian approach for optimal combination of information from different sources. Using simulated GNSS-based water vapor measurements from LEO and ground, we show representative results derived from simple synthetic refractivity fields as well as from a realistic refractivity field based on a European Centre for Medium-Range Weather Forecasts (ECMWF) analysis. For cases located poleward of ∼40° we found a new simple mapping function to perform best within our forward model scheme, where the only free parameter is the climatological scale height in the troposphere, the exact value of which is not critical. The mapping function exploits the ratio between the straight-line ray path length within the first two scale heights above surface and the “effective height” defined by these first two scale heights. We found our technique capable of reconstructing atmospheric features like water vapor maxima near the top of the trade wind inversion. Adjustment of the integral over the water vapor profile measurements to the horizontally averaged ground-based vertical integrated water vapor data efficiently mitigates potential biases in the former data. Accuracies are best in areas with high absolute humidities but also over drier areas such as Finland, useful two-dimensional information can still be obtained. Thus it is attractive to apply the developed technique in a next step to real data.