Objectives:

• Review the state of the art in vegetation fluorescence and biophysical parameter retrievals and exploitation.
• Promote links between classical vegetation remote sensing methods (i.e., multispectral) and new approaches based on fluorescence and high spectral resolution measurements.
• Bring together the vegetation remote sensing community, including data providers, experts and users.
• Provide updates on recent modeling activities coupling remote sensing signals and vegetation physiology and dynamics.
• Plan future activities in the field of vegetation remote sensing exploiting the new observational capabilities.

Topic 1:Synergistic exploitation of top-of-atmosphere radiances from instruments on the FLEX, Sentinel-2 and Sentinel-3 missions.

The simultaneous availability of FLEX, Sentinel-2 and Sentinel-3 data in the 2022+ timeframe represents a unique opportunity of using this data synergistically for vegetation studies.However, the combination of data of such diverse sensors, differing in spatial resolution, angular views and spectral information, requires the development of adequate data fusion techniques. This session will cover different aspects of multi-sensor data fusion methods in preparation for their use in vegetation studies. Geometric co-registration aspects, cartographic projections and resampling issues, cross-calibration methods, data normalization and multi-source data integration aspects will be discussed. Special emphasis will be put on multi-resolution studies (20-300 m) and multi-temporal analysis, the latter exploiting the synergy between the high spatial resolution of Sentinel-2 and high temporal revisit of Sentinel-3 to study vegetation dynamics.

Topic 2: Atmospheric correction, cloud screening and derivation of surface reflectance

The accurate retrieval of land biophysical variables is bounded to a previously performed accurate cloud screening and atmospheric correction, plus a proper derivation of surface reflectance accounting for BRDF effects and other disturbances. Several approaches have been developed for the FLEX, Sentinel-2 and Sentinel-3 missions. Under this topic synergies and complements on the methods implemented for the different missions will be addressed to identify strengths/weaknesses and potential improvements in combined algorithms.

Topic 3: Retrieval of chlorophyll fluorescence emission and vegetation biophysical products

This topic covers latest achievements in the field of sun-induced chlorophyll fluorescence retrievals. Key aspects considered are the strategies to incorporate atmospheric effects in retrievals, and methods to quantify fluorescence at individual wavelengths and the full emission spectrum. Retrieval results are validated by means of measurements and simulations at leaf and canopy scales. To properly interpret the dynamics of vegetation fluorescence, additional vegetation biophysical products are needed to characterize the state of vegetation. Such vegetation products derived from single satellite images include but are not limited to foliage composition (e.g. leaf chlorophyll content), canopy architecture (brown/green/LAI, crown/cover), hemispherically integrated fluorescence fluxes, absorbed photosynthetically active radiation (at leaf and canopy levels) and foliage temperature.

Topic 4: Retrieval of vegetation photosynthetic efficiency and higher level products

Vegetation data products from Sentinel-2, Sentinel-3, and FLEX can be used for the estimation of photosynthetic efficiency and vegetation functioning aspects. Techniques include physically based, statistical models and spectral indices. Products include indicators of photosynthesis rates and vegetation stress, non-photochemical energy dissipation and energy balance aspects.

Topic 5: Models, applications and data assimilation approaches combining fluorescence and multiple vegetation data products

This topic relates to model development and the applications using vegetation fluorescence and vegetation biophysical products in areas such as agriculture/food security, forestry, ecology, and carbon cycle studies. Applications of fluorescence in the derivation of stress indicators are also considered, as well as approaches for data assimilation of fluorescence measurements in Dynamic Global Vegetation Models (DGVM) and other dynamical models (e.g. crop models, ecosystem specific models). Global studies based on available satellite data and regional applications are also considered, as well as requirements of users for scientific research and operational applications.

Topic 6: Product validation / verification and uncertainty estimates

Product validation / verification is a mandatory step prior to the release of data to the user community to ensure the appropriate data product quality. This session will explore the different validation activities for FLEX, Sentinel-2, and Sentinel-3, including comparisons of satellite measurements with in-situ observations, instrumentation and measurements from operational networks, dedicated ground based and airborne campaigns, and inter-sensor comparisons. Special emphasis is put on the characterization of errors in the resulting products and uncertainty estimates for each associated product.