Remote sensing of chlorophyll fluorescence using Unmanned Aerial Vehicles (UAVs)

该项目旨在借助创新的遥感技术提高我们对植物光合作用的理解。小型无人机无人机(UAV)将测量植物的太阳诱导叶绿素荧光(SIF)。SIF能够测量植物的光合作用活性，这些植物在胁迫下，例如由于疾病而下降。通过测量SIF，可以在作物中可见植物胁迫之前检测到它。这种方法为低环境影响和高产量的生态系统和农业研究创造了新的机会。在本研究项目中，将野外光谱仪安装在无人机上来测量SIF。场分光计测量表面反射的光的强度。场分光计能够区分距离较近的波长，这在测量SIF时是必不可少的。一个问题是，SIF信号只占总反射信号的2%，干扰效应可能会混淆该信号。第一个目标是用发光二极管(LED)在荧光波长范围内校准和验证荧光信号。此外，还将检查影响信号的因素：太阳辐射、树叶的质地、植物的垂直结构和飞行高度。为了评估这种影响的空间分布，无人机安装的光谱仪将在感兴趣的区域获取许多点测量数据。可以根据该数据集来内插空间上显式的荧光表面。基于该表面，可以研究信号的空间变化，例如与植物结构有关。信号的变化取决于对整个景观或单个区域的观察。因此，传感器和载体平台根据观测尺度进行调整，例如手持或拖拉机安装的系统、飞机和卫星。总重量不到5公斤的小型无人机通过在离地面100米的高空飞行，在空间数据收集的灵活性和效率方面是多功能和廉价的系统，填补了地面和高空观测之间的空白。将现场光谱仪与现有的地面测量系统(升力传感器)进行比较是这一研究项目的另一个目标，这将改进对SIF信号的解释。这种比较的结果，结合对不同高度信号的分析，可以作为准备卫星飞行任务的基础，例如欧洲FLEX飞行任务。最终，在拟议的DFG项目中捕获的数据将有助于更好地理解不同观测尺度下的SIF信号。

This project aims to improve our understanding of plant photosynthesis with the help of innovative remote sensing technology. A small drone, Unmanned Aerial Vehicle (UAV), will measure the sun-induced chlorophyll fluorescence (SIF) of plants. SIF enables measuring the photosynthetic activity of plants which decreases under stress e.g. through disease. By measuring SIF, plant stress can be detected before it becomes visible in the crop. This method creates new opportunities for the research of ecosystems and agriculture with low environmental impact and high yield.In this research project, a field spectrometer is mounted on a UAV to measure SIF. A field spectrometer measures the intensity of light reflected from a surface. The field spectrometer enables differentiating between closely located wavelengths, which is essential when measuring SIF. One problem is that the SIF signal is only 2% of the total reflectance signal and interference effects can obfuscate this signal. The first objective is to calibrate and validate the fluorescence signal with light-emitting diodes (LEDs) in the fluorescence wavelength range.In addition, factors affecting the signal will be examined: the solar irradiation, the texture of the foliage, the vertical structure of the plants, and flying height. To assess the spatial distribution of such effects, many point measurements will be acquired by the UAV-mounted spectrometer in the area of interest. A spatially-explicit fluorescence surface may be interpolated from this dataset. Based on this surface, the spatial variation of the signal may be investigated, for example in relation to plant structure.The signal varies depending on observing an entire landscape or a single field. As a result, the sensor and the carrier platform are adapted according to the observation scale e.g. hand or tractor-mounted systems, aircraft and satellites. Small drones with a total weight up to 5 kg fill the gap between observations on the ground and in high altitude by flying up to a few 100 m above the surface and being versatile and inexpensive systems with regard to the flexibility and efficiency of spatial data collection.The comparison of the field spectrometer with an established ground-based measurement system (LIFT sensor) is an additional objective of this research project, which will improve interpreting the SIF signal. The findings from this comparison combined with the analysis of the signal in different altitudes can serve as a basis for preparing satellite missions e.g. the European FLEX mission. Ultimately, the data captured in the proposed DFG project will contribute to a better understanding of the SIF signal in different observation scales.