Turpie, K.R., 2013. Explaining the spectral red-edge features of inundated marsh vegetation.

In a previously published experiment, canopy reflectance spectrum was measured for three monospecific canopies as water level was artificially increased. As the water rose, spectral features appeared that could not be explained by the experimenters. To better understand their published results, a combination of a shallow-water reflectance model and a canopy reflectance model was used to simulate the spectral effects observed with increasing levels of inundation. Information from the Lee shallow water, in particular, helped explain the key spectral features observed during high water levels. However, the simulation results also suggested interesting implications regarding the nonlinear mixing of water and vegetation reflection spectra as found in marsh or other flooded canopies. As water level increases, the influence of leaf reflectance below the water's surface changes the characteristics of the background aquatic spectrum. In particular, the simulation yielded a 20-nm shift in the red-edge position as water rose from the bottom to the top of the canopy, which is very similar to the experimental results. This suggests that the interaction of water and chlorophyll absorption features and leaf reflectance near the red-edge of the vegetation spectrum can significantly the influence red-edge position of an inundated canopy. This, in turn, could affect the use of the red-edge position for indicating plant condition in remote-sensing applications of inundated vegetation.