利用GPS的倾斜路径观测暴雨过程中的水汽空间分布

介绍了地基全球定位系统 (GPS) 沿倾斜路径方向观测水汽总量 (SWV) 的原理和方法; 不同时间和不同地点的GPS SWV与微波辐射计反演的SWV符合较好, 误差在3 mm左右, 表明GPS可以较高的精度探测SWV.计算了区域GPS观测网在一次暴雨过程中不同空间方位上的水汽观测结果, 为消除不同路径对SWV的影响, 把SWV转化为天顶方向的值VSWV; 分析了同一GPS站点对不同卫星方向VSWV的变化情况, 以及不同GPS站点对同一个卫星方向VSWV的关系.结果表明, 区域GPS观测网中倾斜路径观测可较好地探测不同方位上水汽的分布和变化; SWV相对于天顶方向的大气水汽总量PW而言, 能更好地代表真实大气水汽分布; 在探空或卫星观测等传统观测手段无法探测的情况下, GPS SWV数据可提供中小尺度暴雨结构中水汽分布和变化状况等有用信息.

Spatial Distribution of Water Vapor Observed with GPS Along Slant Path in a Storm System

Water vapor plays a major role in atmospheric processes but remains difficult to quantify due to its variability at small temporal and spatial scales and the spares set of measurement tools.GPS has proved its ability to monitor the precipitable water vapor at zenith with the same accuracy as other methods.Recent studies have shown that GPS also has the capacity to measure the tropospheric water vapor amount in the line of sight of GPS satellite. This observation can be used to study the nonisotropic distribution of water vapor in space.In this paper,the theory and method of sensing integrated slant path water vapor(SWV) along ray path with ground-based GPS are introduced.The zenith delay is obtained above GPS sites,and then the mapping function and horizontal gradients are used,which are a set of atmospheric parameters estimated by GPS software,to model the water vapor amount along slant path between GPS receiver and GPS satellites.The measurements made at different sites and different time with GPS and water vapor radiometer(WVR) show that RMS error between GPS and WVR is about 3-4 mm.The(agreement) of SWV as measured by GPS and WVR demonstrates the ability of GPS to resolve SWV with high accuracy.In a heavy storm happening in Beijing region,a local GPS network containing 6 GPS sites is used to calculate the zenith precipitable water vapor(PW) and SWV at different directions.The magnitude of SWV is related to the length of ray path.In order to remove the influence of different paths,SWV is converted to the value at the vertical zenith direction(VSWV).The variation of VSWV from the same site to different GPS satellites is analyzed,and the relationship of VSWV from different GPS sites to the same satellite is also presented.The result shows that the distribution and variation of water vapor amount at different directions can be well determined in a local GPS network using the observed GPS SWV.This result is supported by the spatial distribution of GPS PW measured during this storm.When the traditional observation such as radiosondes or satellites cannot work,GPS SWV can provide the useful information of water vapor distribution and variation in the meso-scale storm structure.SWV is a better representation of the actual atmospheric water vapor distribution than PW because SWV contains three dimensional information of water vapor.Using tomographic technique,the three dimensional information of water vapor can be retrieved.Besides the application in water vapor tomography,GPS SWV can be used in many studies,for example,many atmospheric phenomena associated with water vapor transfer,numerical weather prediction and synthetic aperture radar(SAR).