Remote sensing of soil moisture using Rydberg atoms and satellite signals of opportunity

Spaceborne radar remote sensing of the earth system is essential to study natural and man-made changes in the ecosystem, water and energy cycles, weather and air quality, sea level, and surface dynamics. A major challenge with current approaches is the lack of broad spectrum tunability due to narrow band microwave electronics, that limit systems to specific science variable retrievals. This results in a significant limitation in studying dynamic coupled earth system processes such as surface and subsurface hydrology, where broad spectrum radar remote sensing is needed to sense multiple variables simultaneously. Rydberg atomic sensors are highly sensitive broad-spectrum quantum detectors that can be dynamically tuned to cover micro-to-millimeter waves with no requirement for band-specific electronics. Rydberg atomic sensors can use existing transmitted signals such as navigation and communication satellites to enable remote sensing. We demonstrate remote sensing of soil moisture, an important earth system variable, via ground-based radar reflectometry with Rydberg atomic systems. To do this, we sensitize the atoms to XM satellite radio signals and use signal correlations to demonstrate use of these satellite signals for remote sensing of soil moisture – a step towards broad spectrum atomic remote sensing.

星载雷达遥感技术应用于地球系统观测，是研究生态系统、水与能量循环、天气与空气质量、海平面及地表动力学过程中自然与人为变化的核心支撑手段。当前主流技术方案面临的核心瓶颈在于：受限于窄带微波电子器件，无法实现宽频谱可调谐性，这使得遥感系统仅能针对特定科学变量开展反演。这一局限严重制约了对地表与地下水文等动态耦合地球系统过程的研究——此类过程需依托宽频谱雷达遥感技术，才能同时反演多类科学变量。里德伯（Rydberg）原子传感器是一类高灵敏度宽频谱量子探测器，可动态调谐覆盖微波至毫米波频段，且无需依赖特定频段的电子器件。该类传感器可利用导航卫星、通信卫星等现有发射信号完成遥感观测。本研究基于里德伯原子系统，通过地基雷达反射测量技术，实现了对土壤湿度这一关键地球系统变量的遥感观测。为此，我们将里德伯原子调谐至对XM卫星广播信号敏感的状态，并通过信号相关性分析，验证了利用此类卫星信号开展土壤湿度遥感的可行性——这是迈向宽频谱原子遥感的重要一步。