电离层小尺度因素对无线电大气掩星弯曲角的影响

历经25年的发展，基于GNSS的无线电掩星技术已经成为一种有效的临近空间探测手段，但是在无线电大气掩星观测及数据处理过程中不可避免地会受到各种误差的影响，其中，电离层是重要误差源之一。由于电离层小尺度因素的存在，GNSS信号在穿越电离层过程中会受到影响，表现为振幅和相位上的振荡，并最终影响反演所得的大气弯曲角产品。文章基于COSMIC大气弯曲角数据，研究电离层小尺度因素中扩展E层（Es层）及F层不均匀体在中低纬地区对无线电大气掩星的影响，通过计算不同高度区间内的弯曲角偏差标准差统计研究电离层Es层及F层不均匀体发生率与大气弯曲角振荡的关系。结果表明，Es层及F层不均匀体能够引起大气弯曲角振荡，表现出弯曲角随纬度、磁地方时及季节变化的特性，且这些电离层小尺度因素能够影响到的高度区间为35～80 km。该研究有助于进一步认识电离层小尺度因素对GNSS无线电大气掩星探测技术的影响，以及后续提高大气掩星产品的数据质量。

Effect of ionospheric irregularity on GNSS atmospheric radio occultation bending angle

With the development in the past 25 years, the Global Navigation Satellite System (GNSS) atmospheric radio occultation (RO) has been found to be an effective method to detect the near Earth’s space environment. Even though the quality of the RO products is high, the bias still exists and could be reduce the effectiveness of tbe RO, especially, the ionospheric effect on the atmospheric RO. The GNSS signal is affected by the ionospheric irregularity, including the sporadic E (Es) and the F region irregularity, in terms of the oscillations of the amplitude and the phase. This effect could reduce the quality of the atmospheric RO products. In this study, based on the data of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO, the bending angle oscillation, which is defined as the standard deviation of the bias between the observed bending angle and that obtained with the climatology model of the National Center for Atmospheric Research (NCAR), is used for the statistical analysis. The bending angle oscillation in different altitude intervals is studied. It is found that the bending angle oscillation shows significant variations in the latitude, the longitude, and the local time, which is well consistent with the Es and F layer irregularity occurrence features. Besides, the oscillation related to the ionospheric irregularity effect can be observed from 35 km to 80 km in the bending angles. A better understanding of these effects could benefit both the data retrieval and the applications of the RO in the lower atmosphere.