## 3 Results  
The average reflectances of all measured species were typical vegetation reflectance spectra, but still dissimilar when examined in detail (Figure 3). For example, turnip rape had the largest reflectance across the measured spectral range. Wheat had the lowest reflectance in NIR, but the second-highest in red and average in green. The field-measured mean LAI for each species was between 3 and 4 (Table 3), while individual plot-level measurements varied between 1 and 5 (Figure 4a). Cab varied between 25 and 95 \(\mathrm{\SIUnitSymbolMicro g}\) cm\({}^{-2}\) (Table 3, Figure 4a,b). Out had the highest Cab (93 \(\mathrm{\SIUnitSymbolMicro g}\) cm\({}^{-2}\)) and turnip rape the lowest value (32 \(\mathrm{\SIUnitSymbolMicro g}\) cm\({}^{-2}\)). There was a significant (\(p<0.01\)) relationship between the field-measured LAI and Cab, with \(\tau_{k}=0.35\) (Figure 4a), and a weaker (\(\tau_{k}=0.19\)), yet still significant, correlation between the photographic MTA and Cab (Figure 4b). Figure 3: Averaged canopy reflectances (spectral hemispherical-directional reflectance factors) of six crops species acquired from AISA imaging spectrometer data. All used VIs were correlated with LAI in both the field-measured and model-simulated data (Table 4), with \(\tau_{k}\) between 0.34 and 0.64. For the field-measured data (Figure 5), the rank correlation coefficients were all above 0.4, except for MSAVI, MSR\({}_{705}\), and SAVI (\(\tau_{k}\) = 0.34-0.36), and with GARI and GNDVI performing best among the tested VIs (\(\tau_{k}\) = 0.50). In model simulations (Figure 6), GARI and GNDVI produced the lowest \(\tau_{k}\) of 0.38, with BNDVI being the most strongly correlated (\(\tau_{k}\) = 0.64). All the relationships for both empirical analysis and model simulations were significant (\(p\) < 0.01). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Vegetation Index** & **Model Simulation** & **Field Measurements** \\ \hline BNDVI & 0.64 & 0.48 \\ GARI & 0.38 & 0.50 \\ GNDVI & 0.38 & 0.50 \\ MSAVI & 0.38 & 0.34 \\ MSR\({}_{705}\) & 0.39 & 0.36 \\ NDVI & 0.53 & 0.41 \\ SAVI & 0.38 & 0.34 \\ SR & 0.53 & 0.41 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Kendall’s rank correlation coefficient (\(\tau_{k}\)) between vegetation indices and LAI for model simulations and field-measured data. All correlations were statistically significant (\(p\) < 0.01). Figure 4: Correlation between field-measured LAI, the chlorophyll a and b content (Cab), and the leaf mean tilt angle (MTA): (a) field-measured LAI and Cab; (b) photographic MTA and Cab. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Species** & **Average LAI** & **MTA (\({}^{\circ}\))** & **Average Cab (\(\mu\)g cm\({}^{-2}\))** \\ \hline Oat & 3.91 & 58 & 93 \\ Turnip rape & 3.58 & 32 & 33 \\ Barley & 3.74 & 46 & 56 \\ Lupin & 3.46 & 18 & 61 \\ Wheat & 2.96 & 64 & 53 \\ Faba bean & 3.16 & 27 & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Key characteristics of field plots measured in the study. LAI: leaf area index, MTA: mean tilt angle, Cab: chlorophyll a and b content. Figure 5: Correlation between LAI and the selected vegetation indices from imaging spectroscopy data: (**a**) BNDVI, (**b**) GARI, (**c**) GNDVI, (**d**) MSAVI, (**e**) MSR\({}_{705}\), (**f**) NDVI, (**g**) SAVI, (**h**) SR. [PERSON]’s correlation coefficient \(\tau_{k}\) and the significance level \(p\) are given in each plot. Figure 6: Correlation between LAI and the selected vegetation indices according to PROSAIL simulations: (**a**) BNDVI, (**b**) GARI, (**c**) GNDVI, (**d**) MSAVI, (**e**) MSR\({}_{705}\), (**f**) NDVI, (**g**) SAVI, (**h**) SR. [PERSON]’s correlation coefficient \(\tau_{k}\) and the significance level \(p\) are given in each plot. The correlations between VIs and LAI were improved when MTA was fixed, with \(\tau_{k}>0.7\) at all four MTA levels (Table 5).