Unmanned Aerial Vehicle (UAV)-based measurements allow studying sun-induced chlorophyll fluorescence (SIF) at the field scale and can potentially upscale results from ground to airborne/satellite level. The objective of this paper is to present the FluorSpec system providing SIF measurements at the field level onboard a UAV, and to evaluate the potential of this system for understanding diurnal SIF patterns for different arable crops. The core components of FluorSpec are a point spectrometer configured to measure in the O₂ absorption bands at sub-nanometer resolution, bifurcated fibre optics to switch between the downwelling irradiance and upwelling radiance measurements, and a laser range finder allowing accurate atmospheric correction. The processing chain is explained and the capability of the novel Spectral Shape Assumption Fraunhofer Line Discrimination (SSA-FLD) method to retrieve SIF was tested. To test the reliability of FluorSpec diurnal SIF measurements, near-canopy diurnal SIF was monitored during the growing season over potato and sugar beet plants with a ground-based setup. The two crops exhibited a clear diurnal SIF pattern, which positively correlated with the photosynthetically active radiation (PAR). The divergence in diurnal patterns between SIF and PAR indicated that the crops might be suffering from heat stress. A significant correlation between SIF and the Photosystem II Quantum Yield was obtained. By mounting the FluorSpec on a UAV, SIF measurements were obtained over the same crops during a clear day. UAV-based SIF also exhibited a pronounced diurnal pattern similar to the ground-based measurements and it showed clear spatial variation within different crop fields. The obtained results demonstrate the ability of the FluorSpec system to reliably measure plant fluorescence at ground and field level, and the possibility of the UAV-based FluorSpec to bridge the scale gap between different levels of SIF observations.

基于无人机（UAV）的测量可以在野外研究日照引起的叶绿素荧光（SIF），并可能将结果从地面提升到机载/卫星水平。本文的目的是介绍FluorSpec系统，该系统在无人机上提供实地SIF测量，并评估该系统在了解不同耕地作物的日SIF模式方面的潜力。FluorSpec的核心组件是配置为在O _2中进行测量的点光谱仪低于亚纳米分辨率的吸收带，可在下行辐照度和上行辐照度测量之间进行切换的分叉光纤，以及可进行精确大气校正的激光测距仪。解释了处理链，并测试了新的光谱形状假设弗劳恩霍夫线判别（SSA-FLD）方法检索SIF的能力。为了测试FluorSpec昼夜SIF测量的可靠性，在生长期期间，通过地面设置对马铃薯和甜菜植物的近冠日昼SIF进行了监测。两种作物表现出清晰的昼夜SIF模式，与光合有效辐射（PAR）正相关。SIF和PAR之间的昼夜模式差异表明，农作物可能正在遭受热胁迫。获得了SIF与Photosystem II量子产率之间的显着相关性。通过将FluorSpec安装在无人机上，可以在晴朗的一天对相同作物进行SIF测量。基于无人机的SIF还表现出明显的昼夜模式，类似于基于地面的测量，并且在不同作物田间显示出明显的空间变化。获得的结果证明了FluorSpec系统在地面和田野水平上可靠地测量植物荧光的能力，以及基于无人飞行器的FluorSpec弥合了不同水平的SIF观测之间的尺度差距的可能性。基于无人机的SIF还表现出明显的昼夜模式，类似于基于地面的测量，并且在不同作物田间显示出明显的空间变化。获得的结果证明了FluorSpec系统在地面和田野水平上可靠地测量植物荧光的能力，以及基于无人飞行器的FluorSpec弥合了不同水平的SIF观测之间的尺度差距的可能性。基于无人机的SIF还表现出明显的昼夜模式，类似于基于地面的测量，并且在不同作物田间显示出明显的空间变化。获得的结果证明了FluorSpec系统在地面和田野水平上可靠地测量植物荧光的能力，以及基于无人飞行器的FluorSpec弥合了不同水平的SIF观测之间的尺度差距的可能性。