Remote Sensing of Sun-induced Fluorescence to Measure the Functional Regulation of Photosynthesis

Abstract:

Photosynthesis is the ultimate process that determines crop performance. Changes in environmental conditions subject vegetation to different stresses determining dynamics of photosynthetic rate. In this context, techniques that allow the quantification of spatial and temporal patterns of photosynthesis at different scales would be of great use.

Hyperspectral reflectance techniques have often failed to quantify actual photosynthetic light use efficiency and only allow measuring pigment content and canopy structure. Alternatively passive detection of Sun Induced Chlorophyll Fluorescence (SIF) has the potential to be used in the quantification of the actual photosynthetic rate. Chlorophyll fluorescence is emitted from the core of the photosynthetic machinery and is closely related to vegetation stress, reflecting functional limitations of photosynthetic carbon gain.

In this study we aim to assess the potential of SIF to quantify the functional status of photosynthesis in crops. Hereby we present a summary of results obtained at different vegetation levels. Applying the Fraunhofer Line Depth (FLD) principle we estimated SIF from point and imaging hyperspectral data at leaf and canopy level. For the larger scale, the data were collected using HyPlant, the high performance airborne imaging spectrometer.

We expect that local and airborne measurements will greatly facility the development of a potential satellite mission FLEX (FLuorescence Explorer), which is currently under evaluation by the European Space Agency. The FLEX mission proposed to launch a satellite for the global monitoring of steady-state chlorophyll fluorescence in terrestrial vegetation.