Abstract
In the last decade VHR (Very High Resolution) images from satellite, because of the reduced dimensions of pixel (less than 1 meter) and the availability in different acquisition bands (4 or more), have had major dffusion in many application fields of remote sensing. They can be used also to produce high resolution coloured ortho-photos, but adequate levels of positional accuracy as well as small pixel dimensions are necessary. The aim of this paper is to demonstrate that WorldView-2 (WV-2) images satisfy totally these requirements if firstly submitted to high accurate rectification and Pan-Sharpening processes. Using Rational Polynomial Functions (RPFs), original dataset can be better overlapped to cartographic maps at medium or great scale; multispectral images (cell size: 2 m) can be resampled to meet geometric resolution of pan one (cell size: 0.5 m), so detailed and attendible RGB composition results. Applications are carried out on one sample of WV-2 imagery concerning a scene within the Province of Caserta (Italy) that includes vegetated as well as urban areas. Finally RGB composition with pixel dimensions of 0.5 m, positional accuracy less than 1 meter and likely colors are achieved, confirming the possibility to use this type of images for coloured ortho-photos at scale 1:5.000 at least.
Highlights
WorldView-2 (WV-2) was the most technologically-advanced high-resolution satellite ever launched before its twin, WorldView-3, reached orbit
The aim of this study is to demonstrate that WV-2 imagery can be used to produce high resolution coloured ortho-photos: adequate positional accuracy is achieved using georeferencing process based on Rational Polynomial Functions (RPFs) functions (Belfiore & Parente, 2014) while cell size of panchromatic data (0.5 m) is transferred to multispectral ones by Pan-Sharpening (Parente & Santamaria, 2013)
Ground Control Points (GCPs) and Check Points (CPs) are evidenced in Figure 2: their planimetric coordinates in UTM-WGS84 were derived from the above mentioned ortho-photos, while elevations were obtained by DEM available for the area
Summary
WorldView-2 (WV-2) was the most technologically-advanced high-resolution satellite ever launched before its twin, WorldView-3, reached orbit. On board of WV-2 satellite there are two types of sensors that, respectively, collects: panchromatic images (0.450-0.800 μm) with cell size 0.46 m at nadir (0.50 m for commercial uses) and multispectral images (Coastal Blue: 0.400-0.500 μm; Blue: 0.450-0.510 μm; Green 0.510-0.580 μm; Yellow 0.585-0.625 μm: Red 0.630-0.690 μm; Red Edge 0.705-0.7 45 μm; NIR1 0.770-0.895 μm; NIR2 0.860-1.040 μm) with cell size 1.84 m at nadir (2 m for commercial uses). Even if in the last ten years images from space with sub-meter spatial resolution have been available, these data are collected only in four spectral bands (generally named blue, green, red and infra-red), which makes the distinction of land cover classes a difficult task; with the launch of WV-2 for the first time ever, a high spatial resolution space-borne sensor with eight spectral bands ranging from blue to the near infrared parts of the electromagnetic spectrum has been operating, so the possibility to perform classification accuracy has been obtainable (Novack et al, 2011).
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