## 1 Introduction
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Spectral Index** & **Index Name** & **Equation** & **Reference** \\ \hline \multicolumn{4}{l}{_Greenness/Biomass/Canopy structure:_} \\ \hline
1. & NDVI\_a &
\begin{tabular}{l} Normalized Difference Vegetation \\ Index–variant A \\ \end{tabular} & NDVL\_a = (R800 - R670) / (R800 + R670) & [7,9] \\ \hline
2. & NDVI\_b &
\begin{tabular}{l} Normalized Difference Vegetation \\ Index–variant B \\ \end{tabular} & NDVL\_b = (R858–R648) / (R858 + R648) & [18] \\ \hline
3. & RDVI & Renormalized Difference Vegetation Index & RDVI = (R800–R670) / sqrt (R800 + R670) & [19] \\ \hline
4. & NDVI\_705 &
\begin{tabular}{l} Red Edge Normalized Difference Vegetation \\ Index \\ \end{tabular} & NDVL\_705 = (R750–R705) / (R750 + R705) & [20,21] \\ \hline
5. & mNDVL\_705 &
\begin{tabular}{l} Modified Red Edge Normalized Difference \\ Vegetation Index \\ \end{tabular} & mNDVL\_705 = (R750 - R705) / (R750 + R705 - 2R445) & [21,22] \\ \hline
6. & RNDVI & Red Normalized Difference Vegetation Index & RNDVI = (R780 - R670) / (R780 + R670) & [10,23] \\ \hline
7. & GNDVI & Green Normalized Difference Vegetation Index & GNDVI = (R780 - R550) / (R780 + R550) & [23,24] \\ \hline
8. & MSR & Modified Simple Ratio & MSR = ((R800/R670) - 1) / sqrt ((R800/R670) + 1) & [19,25] \\ \hline
9. & SR\_680\_a & Narrowband Simple Ratio 680–variant A & SR\_680\_a = R800 / R680 & [21] \\ \hline
10. & SR\_680\_b & Narrowband Simple Ratio 680–variant B & SR\_680\_b = R900 / R680 & [26] \\ \hline
11. & SR\_705 & Narrowband Simple Ratio 705 & SR\_705 = R750 / R705 & [21] \\ \hline
12. & mSR\_680 & Modified Simple Ratio 680 & mSR\_680 = (R800 - R445) / (R680 - R445) & [21,22] \\ \hline
13. & mSR\_705 & Modified Simple Ratio 705 & mSR\_705 = (R750 - R445) / (R705 - R445) & [21] \\ \hline
14. & RG & Narrowband Red Green Ratio & RG = (R600:R699) / (R500:R599) & [21] \\ \hline \multicolumn{4}{l}{_Pigment activity/Light Use Efficiency:_} \\ \hline
15. & PRI & Photochemical Reflectance Index & PRI = (R531 - R570) / (R531 + R570) & [12-14] \\ \hline
16. & SIPI & Structure Intensive Pigment Index & SIPI = (R800 - R445) / (R800 + R680) & [14] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of SI’s to describe plant ecophysiological parameters reviewed from the literature and used throughout this paper. SI’s are grouped into three general classes showing response to (a) greenness, biomass and structure of the vegetation, (b) light use efficiency, and (c) vegetation and leaf water content. R\({}_{\text{xxx}}\) indicates the reflectance at a specific wavelength (nm). In the following, we want to explore the potential of using hyperspectral indices in order to derive two important land surface parameters most relevant to eco-hydrological applications: (i) LAI, related to vegetation biomass and height, thereby influencing surface roughness and providing exchange area for ecosystem gas and energy transport processes between the vegetation and the atmosphere [34]; also LAI is used as a proxy for the vegetation interception storage, thus controlling important components of the hydrological cycle; and (ii) the availability of root zone soil moisture, being a dominant control on ecosystem water vapor and carbon fluxes, biomass production and crop yield [35]. While both, LAI and root zone WC, are increasingly derived using the inversion of canopy reflectance models in the visible and infrared (LAI, see [36] for an overview) and in the microwave spectral region (WC, e.g., [37, 38, 39]), we here want to restrict our analysis to the use of hyperspectral reflectance data and in particular to the use of individual narrow band ratios (Table 1). There are two main reasons for this: First, the use of simple SI's will be significantly less demanding in terms of computational resources when compared to the inversion of radiation transfer models such as PROSAIL [40] and might therefore be necessary for product development, e.g., with the launch of EnMAP (Environmental Mapping and Analysis Program) envisaged for 2013.