基于微小卫星平台的LEO-LEO微波掩星关键技术的研究

Global climate monitoring is one of the great global challenges, and the occultation technique has a large potential to address the problem. Global navigation satellite system Radio Occultation (GRO) has become a major method to observe the Earth's atmospheric thermodynamic state variables, i.e., pressure, temperature, and humidity as retrieved from refraction measurements using the GNSS radio wave signals. However, in GRO, the temperature and humidity variables in the troposphere can only be retrieved separately from refractivity by co-using a priori humidity and/or temperature information. Fortunately, as an advanced technique beyond GRO, developed over the past two decades, future microwave occultation using centimeter-wave and millimeter-wave signals between Low Earth Orbit satellites (LEO-LEO microwave occultation, LMO), can exploit both the refraction and absorption of the signals to solve the temperature-humidity ambiguity in the troposphere. The Microsat technology has greatly reduced the costs of a constellation of LMO satellites, which creates exciting opportunities for a Microsat-type demonstration mission of LMO. In this research project, we aim to study the key techniques of LMO for a Microsat-type demonstration mission and the research mainly includes the following three objectives. Firstly, the effects of the LEO satellites orbits and attitude, observing instruments and atmospheric propagation environment on the LMO measurements and atmospheric retrievals will be investigated. Secondly, the approach of calculating excess phase and amplitude attenuation from LMO raw observations and orbit data will be established to enhance and improve current LMO simulation system capabilities. Finally, a mountain-based experiment will conducted to verify the simulation and retrieval algorithms. The research results are expected to be significant for the improvement in LMO simulation and retrieval approaches and so for realization of a Microsat-type LMO demonstration mission, which is critical for the monitoring of the global atmosphere.

全球气候监测是人类面临的重大难题，掩星探测技术是解决该问题的有效途径。GNSS无线电掩星探测能提供高垂直分辨率的温、湿、压廓线，但GNSS信号无法区分温度和水汽对其折射率的贡献，存在温度和水汽模糊度问题。LEO-LEO微波掩星大气探测技术（LMO）通过测量水汽吸收带微波信号的相位和幅度，同时反演温度和水汽廓线，从而解决温度和水汽模糊度问题，将为大气探测带来新的变革。微小卫星技术降低了星座组网的成本，为星载LMO探测创造了新机遇。针对基于微小卫星平台的LMO探测的关键问题，拟展开以下工作：①研究LEO卫星轨道和姿态、探测仪器指标和大气传播环境对LMO观测量和反演产品的影响；②开发LMO附加相位和幅度衰减的算法，完善LMO仿真系统；③进行山基实验，验证上述仿真反演算法。本项目旨在揭示卫星定轨和姿控对LMO探测的影响机制，完善LMO仿真反演算法，为实现基于微小卫星平台的LMO探测奠定理论基础。

全球气候监测是人类面临的重大难题，无线电掩星探测技术是解决该问题的有效途径。LEO-LEO微波掩星大气探测技术通过测量水汽吸收带微波信号的相位和幅度，从而解决温度和水汽模糊度问题，同时反演温度和水汽廓线，将成为新一代掩星探测技术的主要发展方向之一。近年来，微小卫星技术蓬勃发展，卫星组网进行掩星探测的成本大大降低，为星载LEO-LEO微波掩星探测创造了新机遇。我国科学家提出了基于小卫星平台的“全球气候与大气成分监测科学实验卫星（CACES）”，LEO-LEO微波掩星探测仪是其有效载荷之一。.本项目围绕实现基于微小卫星平台的LEO-LEO微波掩星探测计划的总目标，开展了以下研究工作：建立了顾及轨道扰动的掩星事件仿真系统，定义了掩星事件全球覆盖率和均匀度概念；仿真分析了LEO卫星轨道参数以及升交点赤经进动对LEO-LEO掩星事件数量和全球覆盖率的影响；揭示了LEO轨道参数对LEO-LEO掩星数量和全球覆盖率的一般规律；评估了LEO星座参数对LEO-LEO掩星探测效能的影响。本项研究为打破目前LEO-LEO掩星系统设计只选取极轨或近极轨的思维定式提供了科学依据；在探测效能方面，当LEO星座卫星数增加到36-72颗时，LEO-LEO掩星事件可在12−18小时内能实现全球100%覆盖。.在电离层和地磁场对无线电掩星探测的影响研究方面，提出了电离层沿“入射线”和“出射线”双边局部球对称假设；并建立了Bi-local弯曲角电离层残差模型；该方法可用于无线电掩星电离层误差修正，也可用于空间环境对无线电掩星探测精度影响的定量分析。开发了地基实验和天基在轨运行模式下，LEO-LEO微波掩星幅度衰减算法，完善了LEO-LEO微波掩星仿真和反演系统；分析了LEO卫星轨道、探测仪器指标和大气传播环境的相关参数对LEO-LEO微波掩星观测量和反演产品精度的影响。在完成本项目的研究内容的同时课题组根据小卫星平台的特点突破了X/K波段天线幅度稳定度控制技术，X/K波段高稳定度功率发射技术和X/K波段高精度测量技术等关键技术，并测试了样机的性能指标。为星载LEO-LEO微波掩星探测的实施提供了理论和技术支撑。