## 4 Methodology
### Definition and Extraction of Features  
Two different information sources have been tested in this work: Landsat 8 time series and a WV2 single image. Several groups of input variables or features were retrieved from both data sources. These object-based features involved spectral information (mean and standard deviation values of all pixels within an object), several vegetation indices (VIs) related to crop vegetation vigor and textural information based on the gray-level co-occurrence matrix (GLCM) proposed by [PERSON] _et al_. [37]. In the case of the Landsat 8 time series, the considered object-based features (Table 3) were computed from the seven bands in both visible and SWIR regions included in the eight pan-sharpened Landsat 8 orthoimages. For WV2, the eight bands provided by the MS single orthoimage were used to obtain the object-based features shown in Table 4. In regard to GLCM features, only three out of 14 originally proposed by [PERSON] _et al_. [37] were finally considered. Homogeneity, dissimilarity and entropy texture features were always computed considering all of the directions over the NIR region (_i.e._, NIR1 and NIR2 bands in the case of WV2 and the NIR band when the Landsat time series were analyzed). The same subset of GLCM features was selected by [PERSON] _et al_. [24]. Lastly, most of the VIs tested in the case of WV2 were adapted for this satellite by [PERSON] and [PERSON] [38]. Figure 2: Location of the 694 reference greenhouses on the WorldView-2 (WV2) orthoimage and existing crops in autumn 2013. Coordinate system: ETRS89 UTM Zone 30N. **7386** \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Tested Features** & **Description** & **Reference** \\ \hline Spectral & Mean and standard deviation (SD) & Mean and SD of each WV2 MS band & [39] \\ \hline \multicolumn{3}{c}{WBI (water band index)} & NIR1/NIR2 & [38] \\ \hline CSI (Carter stress index) & R/NIR1 & [38] \\ \hline CRI (carotenoid reflectance index) & (1/G) \(-\) (1/R) & [38] \\ \hline PSRI (plant senescence reflectance index) & (R \(-\) B)/RE & [38] \\ \hline SIPI (structure insensitive pigment index) & (NIR1 \(-\) C)(NIR1 \(-\) R) & [38] \\ \hline PRI (photochemical reflectance index) & (B \(-\) G)(B \(+\) G) & [38] \\ \hline SR (simple ratio) & NIR2/R & [38] \\ \hline NDVI (Normalized Difference VI) & (NIR2 \(-\) R)(NIR2 \(+\) R) & [38] \\ \hline \multirow{3}{*}{Indices} & (\((2.5\times\) (NIR2\(-\)R))(NIR2 \(+\) (6 \(\times\) R) \(-\) (7.5 \(\times\) B) \(+\) 1)) & [38] \\ \cline{2-3}  & ARVI (atmospheric resistance VI) & (NIR2 \(-\) (2 \(\times\) R \(-\) B))(NIR2 \(+\) (2 \(\times\) R \(-\) B)) & [38] \\ \cline{2-3}  & DMI (Datt/Maccioni index) & (NIR1 \(-\) RE)(NIR1 \(-\) R) & [38] \\ \hline \multicolumn{3}{c}{FFRI (far-red to red index)} & RE/R & [38] \\ \hline LRES (lower red edge slope) & (RE \(-\) R)(710 \(-\) 690) & [38] \\ \hline TRES (total red edge slope) & (RE \(-\) R)(740 \(-\) 690) & [38] \\ \hline RGI (red green ratio index) & R/G & [38] \\ \hline VOGRE (Vogelmann Red Edge) & RE/R & [38] \\ \hline GNDV1\(i\) (green NDVI1) & (NIR1 \(-\) G)(NIR1 \(+\) G) & [41] \\ \hline GNDV1\(j\) (green NDVI2) & (NIR2 \(-\) G)(NIR2 \(+\) G) & [41] \\ \hline GVI (Green Vegetation Index) & (G \(-\) R)(G \(+\) R) & [41] \\ \hline MSR\({}_{1}\) (modified simple ratio) & ((NIR1/R) \(-\) 1)((NIR1/R)\({}^{0.5}+\) 1) & [42] \\ \hline MSR\({}_{2}\) (modified simple ratio) & ((NIR2/R) \(-\) 1)((NIR2/R)\({}^{0.5}+\) 1) & [42] \\ \hline \end{tabular}
\end{table} 
Table 4: WV2 multispectral (MS) single orthoimage object-based features.