Spatial and temporal patterns of solar-induced chlorophyll fluorescence from a Finnish boreal landscape: Comparisons from the ground up to space

Remote sensing of the solar-induced chlorophyll fluorescence (F) by vegetation has the potential to provide important information about carbon uptake dynamics in terrestrial ecosystems. Because of the strong physiological link between F and the photosynthetic status, accurate and timely estimates of F over large areas could significantly improve the understanding and predictions of how terrestrial ecosystems respond to climate change. In the past few decades, a number of different techniques and models aimed at retrieving F from remotely sensed measurements of vegetation reflectance were developed and in this study, we took advantage of these new developments to look at the spatial and temporal patterns of F in boreal coniferous forests. The results we present here are part of a larger research project aimed at improving reflectance-based estimates of photosynthesis efficiency and carbon uptake using space-based observations of boreal vegetation. During the summer of 2010, we continuously measured Scots pine (Pinus sylvestris) canopy reflectance using a tower-based spectrometer system (USB-2000+, Ocean Optics, USA) and leaf-level fluorescence using an automated multi channel chlorophyll fluorescence system (MONI-PAM, Heinz Walz GmbH, Germany). These measurements allowed studying the temporal dynamics of canopy-level F and testing methods for extracting F from canopy reflectance. During an intensive airborne campaign in July 2010, we used the University of Edinburgh’s research aircraft equipped with a dual field-of-view spectrometer system (FieldSpec Pro, Analytical Spectral Devices, USA) to repeatedly measure vegetation hyperspectral reflectance over a large area of boreal forest which encompassed the forest canopy sampled by the tower-based system. Airborne- and tower-based estimates of F where correlated to enable studying the spatial and temporal patterns of chlorophyll fluorescence and photosynthetic status over a larger extent of this boreal landscape in Finland. During the airborne campaign, EO-1 Hyperion satellites images encompassing the study region were acquired near-concomitantly with the airborne transects. These satellite images were used, along with the airborne measurements, to study the effect of increasing spatial scale on retrieving F. We further used the airborne- and satellite-based retrievals of F to look at the impact of a 76-year old record heat wave which occurred during the airborne campaign, on the photosynthetic status of boreal coniferous ecosystems over that region.