全球导航卫星反射信号遥感GNSS-R(Global Navigation Satellite System Reflectometry)是近年来新兴的一个学科交叉研究领域。本文在调研分析国内外研究进展的基础上,基于GNSS-R工作原理与技术特征,将GNSS-R遥感观测模式定义为双天线模式DAP(Double Antenna Pattern)和单天线模式SAP(Single Antenna Pattern),并对两种观测模式的特性和共性问题进行分析。初步建立GNSS-R遥感应用体系架构,以陆面遥感应用为例,结合近几年参与的GNSS-R观测试验与模型研究工作,给出两种观测模式下GNSS-R遥感的典型应用实例,以期为中国未来地基、空基和星载GNSS-R遥感观测及应用工作的开展提供参考。
Global Navigation Satellite Systems(GNSS), including the United States Global Positioning System(GPS), Russian GLONASS, the European Union's Galileo, and China's BeiDou, provide L-band microwave signals with high temporal resolution. The applications of GNSS are extended from positioning/navigation to remote sensing. The versatile refracted GNSS signals sound the atmosphere and ionosphere. The reflected signals, which involve measuring the reflections from the Earth, have recently shown their capacity for Earth observations over ocean or land surfaces. This newly developed technique is called GNSS reflectometry(GNSS-R). The structure of GNSS-R observations can be theoretically considered as a bistatic radar. Analyzing the principles and characteristics of GNSS-R, we define GNSS-R observations as two patterns, namely, Double-Antenna Pattern(DAP) and Single-Antenna Pattern(SAP), by using signal-receiving approaches. DAP has two antennas that straightforwardly receive the direct and reflected signals. The main data processing procedure of the DAP is based on the bistatic radar equation. The SAP receives the interference of the direct and reflected signals by using a single antenna. The main data processing procedure of the SAP is based on theories of signal interference. Some special issues related to the DAP and SAP are also illustrated in this study;these issues include the multiple polarization, footprint, and locations of the specular points. An initial frame for GNSS-R applications is also proposed. The results of several ground-based or airborne experiments previously conducted by our group and collaborators are shown to further explain the proposed DAP and SAP patterns. These results include those from both soil moisture and vegetation-water-content retrievals. The next generations of GNSS systems, especially GPS III and BeiDou II, are expected to demonstrate improved performance and increased capabilities to users worldwide. This study may serve as a reference for China's future development of GNSS-R.