Raytracing atmospheric delays in ground-based GNSS reflectometry
Raytracing atmospheric delays in ground-based GNSS reflectometry
复制标题
地面 GNSS 反射计中的光线追踪大气延迟
作者：
T. Nikolaidou;M. Santos;S. Williams;F. Geremia
一些研究已经认识到，全球导航卫星系统反射仪(GNSS-R)会受到大气传播延迟的影响。不幸的是，在同行评议的文献中，几乎没有关于纠正这种影响的方法和算法的信息。我们发展了一种大气射线追踪程序来严格求解地基GNSS-R观测的三点边值问题。我们用真空距离和射电长度来定义反射减去直接延迟或干涉延迟。我们阐明了线折射和角折射在将总延迟分解为沿路径和几何两个分量时所起的作用。我们首次引入了大气几何延迟的两个子分量：几何移位和几何过剩。我们定义了相应的大气测高改正，这是无偏测高反演所必需的。通过模拟，我们研究了一系列典型情况下的干涉大气延迟，其中在低卫星仰角~10米高的空间站的 5°时，干涉大气延迟达到厘米级。我们发现反射面高度和卫星仰角分别与反射面高度和卫星仰角呈线性和指数关系。大气测高修正也发现了类似的趋势，尽管其震级放大了米级。这两个延迟分量在地平线附近相似，而角延迟分量在天顶消失。对于测高改正分量，两者在天顶时都保持非零值。因此，我们量化了GNSS-R海平面反演中的大气偏差。
Several studies have recognized that Global Navigation Satellite System Reflectometry (GNSS-R) is subject to atmospheric propagation delays. Unfortunately, there is little information in the peer-reviewed literature about the methods and algorithms involved in correcting for this effect. We have developed an atmospheric ray-tracing procedure to solve rigorously the three-point boundary value problem of ground-based GNSS-R observations. We defined the reflection-minus-direct or interferometric delay in terms of vacuum distance and radio length. We clarified the roles of linear and angular refraction in splitting the total delay in two components, along-path and geometric. We have introduced for the first time two subcomponents of the atmospheric geometric delay, the geometry shift and the geometric excess. We have defined corresponding atmospheric altimetry corrections necessary for unbiased altimetry retrievals. Using simulations, we examined the interferometric atmospheric delay for a range of typical scenarios, where it attained centimeter-level values at low satellite elevation angles ~ 5° for a 10-m high station. We found a linear and exponential dependence on reflector height and satellite elevation angle, respectively. A similar trend was found for the atmospheric altimetry correction, albeit with an amplified meter-level magnitude. The two delay components were similar near the horizon while the angular one vanished at zenith. For the altimetry correction components, both remained non-zero at zenith. We thus quantified the atmospheric bias in GNSS-R sea level retrievals.