## 4 Results and Discussion
### Spectral Signature of Vegetated Structures
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Spectral Band (nm)**} & \multicolumn{3}{c}{**Field \(R_{\text{ns}}\) (sr\({}^{-1}\))**} & \multicolumn{3}{c}{**Field \(R_{\text{ns},\text{SRF}}\) (sr\({}^{-1}\))**} & \multicolumn{3}{c}{**P\(\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{     }}}}}}}}}}}}}}}\) \\  & & _S. Maritima_ & _S. Anglica_ & _S. Maritima_ & _S. Anglica_ & _S. Maritima_ & _S. Anglica_ \\ \hline \multirow{2}{*}{**Green**} & **560** & 0.007 \(\pm\) 0.002 & 0.019 \(\pm\) 0.003 & - & - & - & - \\  & **500–620** & - & - & 0.006 \(\pm\) 0.004 & 0.017 \(\pm\) 0.004 & 0.015 \(\pm\) 0.001 & 0.018 \(\pm\) 0.001 \\  & **650** & 0.004 \(\pm\) 0.002 & 0.013 \(\pm\) 0.004 & - & - & - & - \\  & **590–710** & - & - & 0.005 \(\pm\) 0.006 & 0.014 \(\pm\) 0.005 & 0.007 \(\pm\) 0.001 & 0.009 \(\pm\) 0.001 \\  & **840** & 0.042 \(\pm\) 0.008 & 0.071 \(\pm\) 0.007 & - & - & - & - \\  & **740–940** & - & - & 0.039 \(\pm\) 0.009 & 0.064 \(\pm\) 0.010 & 0.029 \(\pm\) 0.003 & 0.034 \(\pm\) 0.003 \\ \multirow{2}{*}{**NDVI**} & \(\frac{NIR-Rad}{NIR+Rad}\) & 0.83 \(\pm\) 0.03 & 0.69 \(\pm\) 0.02 & 0.77 \(\pm\) 0.05 & 0.64 \(\pm\) 0.04 & 0.60 \(\pm\) 0.074 & 0.57 \(\pm\) 0.061 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mean (standard deviation) values of field hyperspectral, field SRF-corrected Pleiades, and Pleiades remote sensing reflectance (sr\({}^{-1}\)) in the Green, Red, and NIR bands, and in the NDVI pseudo-band for the same dense and green _Spartina__anglica_ and _Spartina__maritima_ patches (see Figure 6). Field data were acquired on 21 July 2016, and the Pleiades image was acquired on 3 August 2016. Figure 4: Mean field remote sensing reflectance (sr\({}^{-1}\)) spectra of different characteristic substrate types, collected in the study site on 21 July 2016. Colored spectral bands are associated with the blue (B), green (G), red (R), and near-infrared (NIR) channels of the Pleiades-1 satellite images. A comparison of the satellite and field SRF-corrected \(R_{\rm rs}\) shows that they exhibit a similar general spectral behavior, but with significant differences in the magnitude and spectral shape. For instance, the NDVI values associated with _Spartina maritima_ were 0.77 and 0.60 for \(R_{\rm rs,SRF}\) and Pleiades \(R_{\rm rs}\), respectively. Further, it is worth noting that the difference between the _Spartina maritima_ and _Spartina anglica_ NDVI values is significantly lower in the satellite data (0.03) than in the field data (0.13). This reduced capability of discriminating _Spartina maritima_ from _Spartina anglica_ using satellite observations may be related to the scaling factor [26]. Due to the small scale of the _Spartina_ meadow and high spatial heterogeneity of the vegetation cover, the lower the spatial resolution, the lower the radiative contribution of _Spartina_ to the per-pixel \(R_{\rm rs}\) and the higher the contribution of the soil background signal. Maps of the NDVI were generated for the five different dates of the Pleiades images (Figure 6). This index highlights strong seasonal changes, which appear to be primarily related to species phenology and the ephemeral presence of itinerant biological structures (e.g., the presence of biofilm and algae). The global high marsh zone can be clearly identified from the other types of habitat, particularly during spring (April and May), when the NDVIs of _Spartina_ sp. vegetation show particularly higher values than sand and sediment. The results also highlight both seasonal and inter-annual variations of the NDVI signal for the _Spartina_ vegetation. The NDVI does not, by itself, seem to be sufficient to differentiate the two _Spartina_ species, as they present values of the same order of magnitude (Table 2).