【作者】 宫晓艳；

【导师】 胡雄；

【作者基本信息】 中国科学院研究生院（空间科学与应用研究中心） ， 空间物理学， 2009， 博士

【摘要】 近年来,地球大气无线电GPS掩星探测技术作为二十一世纪最先进的空间探测技术之一迅速发展起来,并成为国内外众多学者广泛关注的焦点。GPS掩星探测技术开辟了地球大气探测崭新的思路,可实现对全球范围的大气层和电离层进行探测。其基本原理是:在低轨LEO卫星上安装双频高动态的GPS接收机,对GPS卫星进行临边观测,当电波信号穿过电离层和中性大气层传播时,由于介质垂直折射指数变化,导致对电波的折射作用,使信号路径发生弯曲,由此可反演获得全球大气折射率、气压、密度、温度和水汽压等大气参数剖面及电离层电子密度剖面。掩星探测技术具有高精度、高垂直分辨率、长期稳定、全球覆盖、全天候和花费较低廉等优势,可弥补传统大气探测手段的不足,其探测资料对于提高数值天气预报精度、临近空间环境监测与研究、气候与全球变化研究、大气模式研究和数据同化等方面都具有重要的科学研究意义,在气候学、气象学、电离层和测地学等领域具有重大的科学研究价值和广泛的实际应用前景。本文以大气掩星反演技术为重点,系统介绍了无线电GPS大气掩星技术的基本原理和系统组成,从提高掩星反演精度出发,对几何光学反演方法和滑动谱全息反演方法所涉及的各个关键环节进行了深入的研究和探讨,开发高精度的数据处理算法,并形成拥有自主知识产权的大气掩星数据处理软件;利用该算法对GPS/MET、CHAMP和COSMIC实测大气掩星数据进行反演;本文对大气掩星中影响反演精度的各个误差源进行了全面深入的分析,探讨了大气掩星反演中的误差特性;本文同时对山基掩星观测试验结果进行了分析。本文的主要工作内容如下:1、介绍了无线电掩星仿真技术,利用卫星轨道数据,在给定大气和电离层模式背景的情况下,模拟计算GPS接收机将要接收的电波附加相位。仿真研究是掩星反演精度验证和误差分析的基础,对研究和发展掩星技术具有重要意义。2、深入系统地研究了大气掩星反演中传统的几何光学反演方法,完成和完善了多普勒数据质量检查和控制、数据预处理、局部圆弧中心修正、电离层修正、弯曲角统计优化和质量评估参数计算等关键环节的算法研究,形成空间科学与应用研究中心拥有自主知识产权的大气掩星数据处理软件。本文对GPS/MET、CHAMP和COSMIC实测大气掩星数据进行反演,分别与国际上权威的数据处理中心GFZ和UCAR的反演结果进行了对比分析,并开展了大量数据的统计验证工作。比较分析结果表明了我们的算法具有较高的精度。3、深入分析了大气掩星反演精度的影响因素,分别对卫星测量误差、掩星接收机测量误差和掩星反演算法误差等三大类影响大气掩星反演精度的误差源进行了较系统的总结。并采用仿真研究的方法,对各误差源对反演的影响进行了定量分析,并分析各误差源所带来的掩星反演误差的特点。定量分析了地球扁率和电离层对反演的影响,分析结果表明:反演算法中的局部圆弧中心的修正以及电离层修正,对于高精度的GPS掩星反演是非常重要的;电离层修正残差仍是制约30~60km高度范围内反演精度的重要因素,进一步完善和优化大气掩星反演需要发展新的电离层修正算法。同时分析了GPS和LEO卫星的位置误差、速度误差、卫星时钟的漂移、载波相位观测误差等对反演的影响,给出了定量的分析结果,指出高精度的掩星反演对上述测量精度的需求。4、针对影响低对流层掩星反演的多路径效应问题,研究并实现了全息反演方法之一的滑动谱反演方法,将该方法应用于COSMIC实测掩星数据的反演。通过与UCAR反演结果的对比分析表明:在富含水汽的低对流层区域,相比几何光学反演方法,滑动谱反演方法与UCAR的反演结果更为符合,说明滑动谱反演方法能够有效的减小多路径传播对反演的影响,反演结果更为可靠。5、利用全球探空数据,对COSMIC大气掩星数据进行了比较验证。结果表明,掩星探测大气温度剖面与探空观测结果符合较好,在10~30km的高度范围内,掩星反演温度廓线与探空观测温度廓线的平均偏差小于1K。6、对山基GPS掩星观测进行了研究。利用2005年8月1日至8月29日中国气象局组织实施的河北雾灵山山基GPS掩星观测试验数据,反演得到接收机高度以下的大气折射率剖面,并将反演结果与自动气象站观测结果进行比较,符合较好,说明山基GPS掩星观测对于低层大气环境监测具有重要的应用价值。更多还原

【Abstract】 Recently, radio occultation technique using the Global Position System for observing the Earth’s atmosphere, one of the most advanced space exploring technique in the 21st century, has developed rapidly and become the focus of a lot of scientists both here and abroad. The radio occultation technique gives a new method of exploring the Earth’s atmosphere. This technique can observe global neutral atmosphere and ionosphere. The principle of the technique is to install the GPS receiver at the satellite of LEO and do limb sounding for GPS satellite. When the radio signal spread through the atmosphere and ionosphere, the signal path will be bended because of the variety of refractivity, from which we can retrieve the atmospheric refractivity, pressure, density, temperature, and water vapor, also we can obtain the electron density in the ionosphere. It can operate all weather with long-term stability and global coverage. And its product has high precision. Occultation sounding is the supplement of traditional measurements. The occultation data of global distributed will greatly promote the precision of numerical weather prediction and research on the space near the Earth, and in addition, it can be applied to study on climate and global change. The occultation technique is of great importance to research on atmosphere model and data assimilation. The GPS radio occultation technique has shown a great future in the field of climate, meteorology, ionosphere, and geodesy.This thesis focuses on the retrieval technique of atmospheric occultation. The basic theory and system construction of radio occultation technique are introduced all around. The main arithmetics of geometric optic method and sliding-spectral method in the occultation inversion are studied in-depth. The arithmetics of high precision and the software for processing atmospheric occulation data have been completed. The occultation data of GPS/MET, CHAMP, and COSMIC are processed using the method we developed. Some factors that influence the precision of retrieval and the characteristics in atmospheric inversion are discussed. At the same time, we analyze the data of the experiment of mountain-based radio occultation.The main works can be summarized as following:1. The method for GPS/LEO radio occultation simulation is introduced in this thesis. Using the simulation method, it can be calculated of atmospheric excess phase received by GPS receiver using the satellite orbit data when the atmospheric background is known. Study on simulation is the basic of validate of occultation and error anlysis. And it is important to study and develop occultation technique.2. The geometric optic method in atmospheric occultation inversion is introduced. We discuss some important process in detail, such as check up and control for Doppler shift data, data pretreatment, the local curvature correction, ionospheric calibration, optimal estimation of the bending angle and calculating the parameters of occultation quality. And the software for processing the occultation data is developed. The occultation data of GPS/MET, CHAMP, and COSMIC are processed, and we compare our results and results of GFZ and UCAR. A lot of statistic and validation of data are done in this thesis. Results show that our arithmetic has high precision.3. The factors that affect the precision of atmospheric inversion are discussed in-depth. There are three types of error source in atmospheric occultation included of satellite measurements errors, GPS receiver measurements errors and the errors from the method of inversion. We analyze the error sources using simulative method. And the characteristics in atmospheric inversion are discussed. The effects of The Earth’s oblateness and ionosphere on the retrieval are analyzed. Results show that: local curvature calibration and ionosphere calibration are very important for GPS occultation inversion of high precision. Ionospheric residual influence is the main reason of restricting the retrieval precision from 30 km to 60 km also, and it is necessary to develop new ionosphere calibration method for atmosphere inversion of higher precision. In addition, we analyze effect of the orbit error, velocity error, clock error and shift and observation error of phase of carrier wave on inversion.4. The multipath propagation that affects the inversion in the lower atmosphere is studied. To solve this problem, the sliding-spectral method has been studied. Sliding-spectral method is applied to COSMIC radio occultation event data. Through the comparative analysis of our results and that of UCAR, it can be concluded that sliding-spectral method can reduce the effect of multipath propagation of lower atmosphere, and can retrieve the atmospheric parameters more accurately.5. The COSMIC atmospheric radio occultation data is compared with global radiosondes. The comparison shows that the atmospheric temperature profiles are consistent with radiosondes. The mean difference of temperature between radio occultation and radiosonde is less than 1K from 10km to 30km.6. The mountain-based GPS radio occultation is studied. Using the data from the mountain-based observation experiment at Mt Wuling in Hebei Province during August 1-29, 2005, the profiles below the height of receiver are retrieved successfully. We compared the refractivity of the altitude in which the receiver is located with the result of automatic weather station. The result illustrates a good agreement in mountain-based GPS occultation and automatic weather station. Mountain-based occultation has potential applications for lower atmosphere sounding.更多还原