A ray-tracing operator and its adjoint for the use of GPS/MET refraction angle measurements
A ray-tracing operator and its adjoint for the use of GPS/MET refraction angle measurements
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DOI：
10.1029/1999jd900450
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发表时间：
1999-09
影响因子：
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通讯作者：
X. Zou;F. Vandenberghe;Bin Wang;M. Gorbunov;Y. Kuo;S. Sokolovskiy;J. C. Chang;J. Sela;R. Anthes
中科院分区：
文献类型：
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作者：
X. Zou;F. Vandenberghe;Bin Wang;M. Gorbunov;Y. Kuo;S. Sokolovskiy;J. C. Chang;J. Sela;R. Anthes
用于接收全球定位系统(GPS)信号的小型高性能仪器的发展为利用无线电掩星技术对地球大气层进行主动遥感探测创造了机会。GPS气象学(GPS/MET)实验已经提供了这种能力的原型演示。虽然GPS测量可以得到大气折射率、温度和等压层位势高度的高垂直分辨率剖面，但在许多情况下仍有许多问题需要解决。这些问题包括多路径传播的存在，大气潮湿地区水汽和温度之间的模糊性，以及在折射率水平梯度较大的地区从GPS折射角测量中反演准确的折射率剖面的困难。本文的目的是开始开发一种方法，将GPS“原始”测量(折射角)直接纳入数值天气分析和/或预报系统，以缓解上述问题。首先，开发了一种将大气状态与GPS折射角测量联系起来的光线跟踪观测算子，描述了所涉及的物理和数值计算，并将基于NOAA国家环境预测中心(NCEP)全球分析的模拟折射角与GPS/MET折射角实测值进行了比较。其次，给出了光线跟踪算子的切线型和伴随型。在变分数据分析系统中，直接使用GPS折射角度测量需要这三个运算符。单次观测实验表明，在变分分析中直接使用GPS折射角度会引起温度和比湿度场的变化，这些变化不限于掩星位置，而是在其掩星平面上6300公里的拉长带内。在S水平上，一次掩星的变化发生在以射线近地点为中心的约600公里、3600公里范围内。最后，讨论了利用GPS折射率与折射角的关系的优缺点。还评估了使用局部折射率估计值所产生的误差。
The development of small, high-performance instruments to receive Global Positioning System (GPS) signals has created an opportunity for active remote sounding of the Earth's atmosphere by radio occultation techniques. A prototype demonstration of this capability has been provided by the GPS Meteorology (GPS/MET) experiment. Although it was shown that high vertical resolution profiles of atmospheric refractivity, temperature, and geopotential height of constant pressure levels can be derived from the GPS measurements, with high accuracy under many circumstances, many issues remain. These include the existence of multipath propagation, the ambiguity between water vapor and temperature in moist regions of the atmosphere, and the difficulty in retrieving an accurate refractivity profile from the GPS refraction angle measurements over regions where the horizontal gradient of the refractivity is large. The aim of this paper is to begin the development of a methodology for incorporating the GPS "raw" measurements (refraction angles) directly into numerical weather analysis and/or prediction systems in order to alleviate the above mentioned problems. First, a ray-tracing observation operator that links the atmospheric state to the GPS refraction angle measurements is developed, the physics and numerics involved are described, and the simulated refraction angles, based on the NOAA National Centers for Environmental Prediction (NCEP) global analysis, are compared with the observed GPS/MET refraction angle measurements. Second, the tangent linear and adjoint of the ray-tracing operator are developed. These three operators are required for the direct use of GPS refraction angle measurements in a variational data analysis system. A single observation experiment reveals that the direct use of GPS refraction angles in a variational analysis causes changes in the temperature and specific humidity fields that are not limited to the occultation location but in an elongated band of 6300 km in its occultation plane. On s-levels, changes from the use of one GPS occultation occur in an area of about 600 km 3 600 km large which is centered around the ray perigee point. Finally, the advantages and disadvantages are discussed for the use of the GPS refractivities versus refraction angles. Errors made by using local estimates of refractivity are also assessed.