Effect of bandwidth of panchromatic image on the quality of pansharpened multispectral image

Preservation of the spectral characteristics in multispectral images is important in the development of pansharpening methods because it affects the accuracy of subsequent applications, such as visual interpretation, land cover classification, and change detection. The combinations of the spectral properties (observation wavelength and width of spectral bands) of multispectral and panchromatic images affect both the spatial and spectral quality of pansharpened images. Therefore, the clarification of the relations between spectral bands and quality of pansharpened image is important for improving our understanding of pansharpening methods, and for developing better schemes for image fusion. The objective of this study is to investigate the effect of bandwidth of panchromatic image on the spectral quality of pansharpened multispectral image by the simulation using hyperspectral data. Fifty-four panchromatic images with shifting bandwidths were generated using airborne hyperspectral data by averaging of different band combinations. Four bands of multispectral images were generated similarly from hyperspectral data, and spatially degraded by a factor of 6 in order to simulate low-resolution images. The pansharpened multispectral images were produced from these multispectral and panchromatic data by means of 5 pansharpening methods. The results were evaluated by the comparison with the non-degraded multispectral bands both qualitatively by visual assessment, and quantitatively by statistical index ERGAS. Quality of near infrared band was worse than visible bands, mainly due to the spectral position of panchromatic band in visible wave region. It was, however, gradually improved as longer bandwidth of panchromatic band that was expanded into near infrared region. Gram-Schmidt Spectral Sharpening generated somewhat better quality among the method from the view point of ERGAS. It was concluded that wider spectral bandwidth resulted in balanced quality of images in all bands, though the appearances of images are rather dissimilar to the original.