Towards global mapping of Canopy Chlorophyll Content from sentinel 2

Quantifying Canopy chlorophyll content (CCC) is fundamental for the understanding of terrestrial ecosystems through monitoring and evaluating terrestrial ecosystem properties such as carbon and water fluxes, productivity, light use efficiency as well as nutritional and environmental stresses. Information on the amount and distribution of CCC helps to assess and report biodiversity indicators related to ecosystem processes and functional aspects of biodiversity. However, robust and rigorous methods for regional and global mapping of CCC from remote sensing data is not well defined. This study aimed at evaluating the spatiotemporal consistency and scalability retrieval methods for large scale mapping of CCC. Four methods (i.e., Radiative transfer models (RTMs) inversion using look-up table (LUT), the Sentinel application platform (SNAP toolbox), simple ratio vegetation index (SRVI), and partial least square regression (PLSR), were investigated for their performance across biomes. Statistical measures were computed and spatiotemporal consistency pairwise comparison applied to evaluate the similarities and differences among CCC products generated by the four methods in four biomes (Temperate forest, Tropical forest, wetland, and Arctic Tundra). All the tested methods, except PLSR showed similar patterns and no significant difference in the spatial distribution in temperate forests. The CCC products obtained using the SRVI and the SNAP toolbox approach result in a systematic over/under-estimation of CCC. RTMs inversion by LUT (INFORM and PROSAIL) resulted in a non-biased, spatiotemporally consistent predictions of CCC with range closer to expectations. Therefore, the RTM inversion using LUT approaches, particularly INFORM for ‘forest’ and PROSAIL for ‘short vegetation’ ecosystems are recommended for CCC mapping from Sentinel-2 data for regional and global mapping of CCC. Further validation of the two RTMs using in situ CCC data in different terrestrial biomes is required in the future.