Challenges in the atmospheric characterization for the retrieval of spectrally resolved fluorescence and PRI region dynamics from space
Abstract In the coming years, Earth Observation missions like the FLuorescence EXplorer (FLEX) will acquire the radiance signal from the visible to the near infrared at a very high spectral resolution, enabling exciting prospects for new insights in satellite based photosynthetic studies. In this context, the process of de coupling atmospheric and vegetation related spectral signatures will become essential to guarantee a reliable estimation of the vegetation photosynthetic activity from space. Dynamic changes related to the vegetation photosynthetic status result in subtle contributions to the top of atmosphere radiance signal, e.g. due to the emission of the solar induced chlorophyll fluorescence 650 800 nm) or due to changes in surface reflectance spectra (500 600 nm) indicating variations in the vegetation photoprotection and light use efficiency. Conversely, atmospheric effects (molecular and aerosol absorption and scattering) dominate the spectral interval of interest for vegetation studies. This article presents a comprehensive overview of the atmospheric radiative effects caused by aerosols, ozone (O3) water vapor (H2O) oxygen (O2) and atmospheric pressure and temperature changes within the visible and near infrared spectral interval, and paying special attention to the co occurring vegetation related spectral changes associated with the fluorescence emission and the activation of the photoprotection mechanisms. Since the largest uncertainties in the atmospheric correction process are associated with the characterization of the aerosol radiative effects, this work largely concentrates on the satellite retrieval related implications under different aerosol absorbing and scattering scenarios on a global scale. Through a simulation exercise, it is evaluated to what extent aerosol climatology could influence the accuracy of satellite derived surface apparent reflectance spectra impacting; therefore, any vegetation related satellite product on a seasonal and global scale.