区域尺度无人机涡动相关通量观测系统的应用研究

陆地生态系统的水热循环与碳循环是陆地表层系统中物质能量循环的核心，其中区域尺度地表水、热、碳通量的直接观测是当下陆地生态系统通量观测与模拟研究中的热点与难点。机载涡动相关方法能够直接观测区域尺度生态系统通量，基于无人机平台的涡动相关通量观测技术同时兼具了区域覆盖性与经济灵活性等优点，是机载通量观测技术的最新发展方向。在介绍机载涡动相关通量观测方法的主要技术原理、观测特点以及无人机通量观测系统组成的基础上，通过在相对均匀的区域开展无人机与地面通量观测对比试验，采用谱分析、观测结果对比以及源区分析等方式对无人机通量观测系统的性能进行了初步评价。结果表明：无人机通量观测系统能够实现对大气高频湍流信号的有效采样；无人机与地面观测的湍流通量具有较好的一致性，但是感热和CO₂通量出现了低估、潜热和摩擦风速出现了高估；观测平台与仪器的差异、垂直通量辐散、大气边界层条件、不同的地面源区及地表异质性的影响是造成二者差异的潜在主要因素。最后对未来研究目标进行了展望，以进一步推动该技术在相关领域中的应用。

Study on application of the regional scale UAV-based flux measurement system

Water, heat, and carbon cycle of the terrestrial ecosystems are the core of the matter and energy cycle in the land surface system. The direct measurement of land surface water, heat, and carbon fluxes at the regional scale has always been a hotspot and a gordian knot in the study of the ecosystem flux observation and simulation. Airborne eddy covariance flux measurement method can directly measure ecosystem fluxes at the regional scale. The unmanned aerial vehicle (UAV)-based eddy covariance flux measurement has the advantages of regional coverage and economy flexibility, and is the latest development direction of the airborne flux measurement method. This study firstly introduced the basic technical principle, observation characteristics, and the system construction of the UAV-based flux measurement system. Then, a comparison experiment between UAV and ground flux measurement was carried out over a typical homogeneous surface. The performance of the UAV-based flux measurement system was preliminarily evaluated by spectral analysis, fluxes comparison, and footprint analysis. The results show that the UAV-based flux measurement system could effectively sample the high-frequency turbulence signals. The turbulent fluxes measured by UAV were basically consistent with those measured from ground. However, compared with ground measurements, the UAV underestimated the sensible heat and CO₂ fluxes and overestimated the latent heat fluxes and friction velocity. The main potential reasons causing the mismatching between the UAV and ground fluxes measurements are attribute to the effects including the differences in measurement platform and instruments, vertical flux divergence, atmospheric boundary layer condition, and the differences in footprint areas as well as the influence from surface heterogeneity. At last, we proposed the future work to promote the study and the application of the UAV-based flux measurement in the relevant fields.