Abstract
Despite the lowtree diversity and scarcity of the understory vegetation, the highmorphologicalplasticity of mangrove trees induces, at the stand level, a very large variability of forest structuresthat need to be mapped for assessing the functioning of such complex ecosystems. Fully constrainedlinear spectral unmixing (FCLSU) of very high spatial resolution (VHSR) multispectral images wastested to fine-scale map mangrove zonations in terms of horizontal variation of forest structure.The study was carried out on three Pleiades-1A satellite images covering French island territorieslocated in the Atlantic, Indian, and Pacific Oceans, namely Guadeloupe, Mayotte, and New Caledoniaarchipelagos. In each image, FCLSU was trained from the delineation of areas exclusively related tofour components including either pure vegetation, soil (ferns included), water, or shadows. It was thenapplied to the whole mangrove cover imaged for each island and yielded the respective contributionsof those four components for each image pixel. On the forest stand scale, the results interestinglyindicated a close correlation between FCLSU-derived vegetation fractions and canopy closureestimated from hemispherical photographs (R2 = 0.95) and a weak relation with the NormalizedDifference Vegetation Index (R2 = 0.29). Classification of these fractions also offered the opportunityto detect and map horizontal patterns of mangrove structure in a given site. K-means classificationsof fraction indeed showed a global view of mangrove structure organization in the three sites,complementary to the outputs obtained from spectral data analysis. Our findings suggest that thepixel intensity decomposition applied to VHSR multispectral satellite images can be a simple butvaluable approach for (i) mangrove canopy monitoring and (ii) mangrove forest structure analysisin the perspective of assessing mangrove dynamics and productivity. As with Lidar-based surveys,these potential new mapping capabilities deserve further physically based interpretation of sunlightscattering mechanisms within forest canopy.