Solar-induced Chlorophyll Fluorescence Extraction and Validation at Airborne Level Based on an Unmanned Airship

Passive remote sensing (RS) of solar-induced chlorophyll fluorescence (SIF) of vegetation is feasible at ground level, airborne level and space borne level with certain prototypes. Fraunhofer Line Discrimination (FLD) and its improved methods have been widely used to extract SIF. Unlike processing at ground level, these methods do not work so well since it is not easy to obtain the solar incident irradiance (SI) at airborne level, which is the key to calculating SIF. This paper adopts three strategies to extract SIF at airborne level. 1. Simultaneously measure SI at ground level. 2. Measure SI and acquire the hyperspectral image concurrently at airborne level. 3. Detect SIF with aFLD method which calculates SIF by comparing the radiance of the non-fluorescing target and vegetation. And then the validation and evaluation works were done with ground level measurements. The SIF values Fairborne SI_air calculated with airborne SI measurement are close to SIF at ground Fground, about 30% higher. However, the SIF Fairborne SI_ground with ground based SI are mostly negative. As to aFLD method, cement ground, water and roof are used, the results Fairborne roof and Fairborne water based on the roof and water are all negative. Cement ground works better according to the same size relation of three crops with Fground ( Fsoybean >Fmillet >Fpeanut ), while the SIF value Fairborne cement is much higher than the all crops’ Fground about 150%. The results show that the SI measured at ground level may have some problems for extracting SIF at airborne level. Method with SI measured at airborne level is best among these strategies. Also, this study proved that cement acted as the non-fluorescing target performs well in aFLD.