WorldView-2 image

WorldView-2 imagery covering the visible to near-infrared range of the electromagnetic spectrum was obtained for the same dry winter period (May−June 2017) as the field survey period. WorldView-2 image has high spectral and spatial resolutions making it effective for fine-scale woody plant species diversity estimation [51]. Specifically, the image has eight multispectral bands between 0.40 and 1.04 μm at 1.8 m spatial resolution and a panchromatic band covering 0.45−0.80 μm at 0.5 m spatial resolution (DigitalGlobe, www.digitalglobe.com). The bands vary in width with the yellow (0.59 and 0.63 μm) and red edge (0.71 and 0.75 μm) bands being narrower than the others. The coastal band (0.40−0.46 μm) was excluded from the analysis due to its relative sensitivity to atmospheric interferences [50]. Following a comparison of Dark Object Subtraction (DOS), [52], Fast Line-of-sight Atmospheric Analysis of Hypercubes (FLASH), [53] and QUick Atmospheric Correction (QUAC), [54] methods that yielded similar reflectance values (Pearson’s correlation, r = 0.99)). We applied the DOS method implemented in ENVI 5.3 ©2015 (Exelis Visual Information Solution Inc., Boulder, Colorado). Subsequently, the spatial resolution of the atmospheric corrected multispectral bands was pan-sharpened to 0.5 m. (Fig 2). The reliability of our pan-sharpening was ascertained by comparing the results with the already pan-sharpened image provided by the data supplier (DigitalGlobe, www.digitalglobe.com).