## 3 Datasets  
### WorldView-2 Data  
WorldView-2 (WV2) is a very high-resolution (VHR) satellite launched in October 2009. This sensor is capable of acquiring optical images with 0.46-m and 1.84-m ground sample distance (GSD) at nadir in panchromatic (PAN) and multispectral (MS) mode, respectively. Moreover, it was the first VHR commercially available 8-band MS satellite: coastal (C, 400-450 nm), blue (B, 450-510 nm), green (G, 510-580 nm), yellow (Y, 585-625 nm), red (R, 630-690 nm), red edge (RE, 705-745 nm), near infrared-1 (NIR1, 760-895 nm) and near infrared-2 (NIR2, 860-1040 nm).  
A single WV2 image taken on 30 September 2013, over the study area was acquired. It was collected in Ortho Ready Standard Level-2A (ORS2A) format, containing both PAN and MS imagery. This satellite image had a mean off-nadir view angle of 11.8\({}^{\circ}\), a mean collection azimuth of 38.2\({}^{\circ}\) and 0% of cloud cover. The final product GSD was of 0.4 m and 1.6 m for PAN and MS images, respectively. WV2 ORS2A format presents both radiometric and geometric corrections. These types of images are georeferenced to a cartographic projection using a surface with constant height and include the corresponding RPC sensor camera model and metadata file. The delivered products were ordered with a dynamic range of 11-bit and without the application of the dynamic range adjustment preprocessing (_i.e._, maintaining absolute radiometric accuracy and full dynamic range for scientific applications).  
From this WV2 ORS2A bundle image, a pan-sharpened image with 0.4-m GSD was attained by means of the PANSHARP module included in Geomatica v. 2014 (PCI Geomatics, Richmond Hill,  
Figure 1: Location of the study area on a RGB Landsat 8 image taken in August 2013, covering the “Poniente” region. Coordinate system: ETRS89 UTM Zone 30N.  
ON, Canada). The coordinates of seven ground control points (GCPs) and 32 independent check points (ICPs) were obtained by the differential global positioning system (DGPS) using a total GPS Topcon HiPer PRO station working in real-time kinematic mode (RTK). The ground points (both GCPs and ICPs) were measured with reference to the European Terrestrial Reference System 1989 (ETRS89) and UTM Zone 30 projection. A pan-sharpened RGB orthoimage with 0.4-m GSD was generated by using the seven GCPs to compute the sensor model based on rational functions refined by a zero order transformation in the image space (RPC0). A medium resolution 10-m grid spacing DEM with a vertical accuracy of 1.34 m (root mean square error; RMSE), provided by the Andalusia Government, was used to carry out the orthorectification process. The planimetric accuracy (RMSE\({}_{\rm 2D}\)) attained on the orthorectified pan-sharpened image and measured on 32 ICPs was 0.59 m.  
Furthermore, an MS orthoimage with 1.6-m GSD and containing the full 8-band spectral information was also produced. The same seven GCPs, RPC0 model and DEM were used to attain the MS orthoimage. It is worth noting that atmospheric correction is especially important in those cases where multi-temporal or multi-sensor images are analyzed [24, 25, 27, 28, 29, 30]. Thus, in this case and as a prior step to the orthorectification process, the original WV2 MS image was atmospherically corrected by using the ATCOR (atmospheric correction) module included in Geomatica v. 2014. This absolute atmospheric correction algorithm involves the conversion of the original raw digital numbers to ground reflectance values, and it is based on the MODTRAN (MODerate resolution atmospheric TRANmission) radiative transfer code [31]. Finally, an atmospherically-corrected WV2 MS orthoimage with a RMSE\({}_{\rm 2D}\) of 2.20 m was generated.