中文摘要：

月球电离层的存在是一个具有争议性的问题.迄今为止,前苏联、美国、欧洲和日本先后采用掩星及就位观测手段对月球电离层进行了探测,探测结果存在一定差异.为探测及研究月球电离层,利用我国月球探测工程再入返回飞行器服务舱在地面测量站开展了自主的S/X相干双频掩星观测.本文采用本地相关处理方法提取各频点连续精确的相位信息,初步获得了月球电离层电子柱浓度的探测结果,证实了月球电离层的存在,同时提出了新问题：为什么存在如此强的月球电离层？

英文摘要：

The existence of lunar ionosphere has been under debate for a long time. In Apollo 14 mission, the electron density detected by the charged particle lunar environment experiment （CPLEE） was 104 el/cm3 at several hundred meters high during lunar day time. In Luna-19/22 mission, the electron density profiles were detect and the peak densities were about 103 el/cm3. In the last decade, European mission SMART-1 and Japanese mission SELENE also performed radio occultation experiment for lunar ionosphere. The results of these missions don＇t well-matched. In order to explore the lunar ionosphere, a very low frequency radio astronomical payload has been suggested to be sent to the surface of lunar far-side by the Chinese Chang＇E-4 lunar lander mission in 2019. The payload will record the Type II solar burst, which may cover the frequency of electro-magnetic wave as low as several dozen kilo-Herz. The possible lunar ionosphere above the payload with certain electron density may truncate or block the solar burst signal as corresponding plasma frequency. To estimate the possible truncate frequencies for these observations by the new kind of payload, and to determine the lunar ionospheric distribution, an lunar radio occultation experiment with the service module of Chinese circumlunar return and reentry spacecraft has been performing. The circumlunar return and reentry spacecraft is a Chinese precursor mission for the Chinese lunar sample return mission. It was launched on 23 October 2014. After the return and reentry experiments, the service module went back into a Lunar Orbit on 11 January 2015 to image the target landing zone for the Chinese lunar sample return mission which has not yet been disclosed. During this period, the radio occultation experiments have been performed to detect the lunar ionosphere. The service module provides a stable and reliable frequency source, whose short-term stability is n×10-9, for both X-band and S-band signal. The signals transmitted from the spacecraft in S and X band passed t