基于低空成像高光谱系统探测植被日光诱导叶绿素荧光

Remote Sensing of Chlorophyll Fluorescence at Airborne Level Based on Unmanned Airship Platform and Hyperspectral Sensor

植被叶绿素荧光与光合作用关系密切,被认为是光合作用的有效探针。该研究利用成像高光谱传感器和无人飞艇构建了一套适用于低空叶绿素荧光探测的系统。针对低空叶绿素荧光探测中,太阳下行辐射光谱难以获取的情况,基于已有的aFLD方法,提出一种新的叶绿素荧光提取方法a3FLD,该方法利用了非荧光发射体,且考虑植被反射率在夫琅和费线附近的变化。通过模拟数据以及实测数据对两种提取结果进行了比较。模拟数据分析结果显示:当地物的反射率在夫琅和费线附近存在一定的变化时,a3FLD计算得到的荧光值误差小于aFLD,地物反射率变化越大,a3FLD的改进越明显。对低空高光谱影像数据的分析显示:aFLD和a3FLD提取不同植被的日光诱导叶绿素荧光相对大小关系相一致,与作物所处的生长阶段吻合。但aFLD荧光提取值比a3FLD高15%左右。aFLD的结果中有部分非荧光发射体得到较强荧光,a3FLD能改进此问题。结果显示,利用该系统和方法能够成功地提取到植被叶绿素荧光,且所提出a3FLD方法提取的结果优于aFLD方法。

The solar-induced chlorophyll fluorescence （ChlF） has a close relationship with photosynthetic and is considered as a probe of plant photosynthetic activity. In this study, an airborne fluorescence detecting system was constructed by using a hyper spectral imager on board an unmanned airship. Both Fraunhofer Line Discriminator （FLD） and 3FLD used to extract ChlF re quire the incident solar irradiance, which is always difficult to receive at airborne level. Alternative FLD （aFLD） can overcome the problem by selecting non-fluorescent emitter in the image. However, aFLD is based on the assumption that reflectance is i dentical around the Fraunhofer line, which is not realistic. A new method, a3FLD, is proposed, which assumes that reflectance varies linearly with the wavelength around Fraunhofer line. The result of simulated data shows that ChlF retrieval error of a3FLD is significantly lower than that of aFLD when vegetation reflectance varies near the Fraunhofer line. The results of hyper spectral remote sensing data with the airborne fluorescence detecting system show that the relative values of retrieved ChlF of 5 kinds of plants extracted by both aFLD and a3FLD are consistent with vegetation growth stage and the ground-level ChlK The ChlF values of aFLD are about 15% greater than a3FLD. In addition, using aFLD, some non-fluorescent objects have considera ble ChlF value, while a3FLD can effectively overcome the problem.