A status report after a decade of remotely sensed Solar Induced Fluorescence (SIF)

Leaf fluorescence is a natural process by which chlorophyll pigments relax part of the electromagnetic energy they absorb in the form of electromagnetic energy of lower intensity. Chlorophyll fluorescence happens in the photosynthetic apparatus and is tightly linked to processes generating reduction power and energy to drive carbon assimilation. For more than 40 years, scientists measured plant photosynthesis using Pulse-Amplitude-Modulation (PAM) chlorophyll fluorometer, an apparatus where fluorescence is measured upon actinic illumination and saturating pulse of light to retrieve quantum yield for photosynthesis.

A little more than a decade ago, a breakthrough in spatial earth observation occurred: using narrow band observations in the oxygen A-band, the first global Solar Induced Chlorophyll Fluorescence (SIF) measurements were obtained. For the first time, the scientific community had access to observations directedly linked to photosynthetic processes arousing high expectations to constrain carbon uptake by terrestrial vegetation.

In this study we assess to what extend these expectations have been met though an extended literature review. In addition, as SIF measurements are also linked to the vegetation structure and how an emitted photon escape the canopy, we will discuss the influence of the canopy structure in SIF measurements. We will also compare SIF products from different platforms in term of fluorescence yield, which is the first step to evaluate photochemical yield.  Finally, we will discuss difficulties arising when comparing vegetation models simulations and SIF measurements.