DSCOKRI: A library of computer programs for downscaling cokriging in support of remote sensing applications

The main purpose of this paper is to describe and provide a suite of computer programs for performing downscaling cokriging with satellite sensor images. The usual setting of downscaling cokriging is to increase the spatial resolution of multispectral images with coarse spatial resolution by fusing them with a fine spatial resolution image of a different band from the same or a different sensor. This problem has also been described as image sharpening and commonly the spatial resolution of the fused image is equal to the finest spatial resolution used in the fusion. Nevertheless, downscaling cokriging allows the spatial resolution of the predicted image to be increased beyond that of any of the input data sets, a procedure usually referred to as super-resolution sharpening. The programs provided here support all the required stages for image fusion and super-resolution sharpening by downscaling cokriging. These stages are: (i) compute the empirical variogram of each spectral band and empirical cross-variograms for each pair of spectral bands; (ii) estimate and fit a model to the point-support variogram of each spectral band and cross-variogram of each pair of spectral bands; (iii) set up the cokriging system and obtain the set of downscaling cokriging weights and (iv) obtain the sharpened image by application of the weights to the empirical remote sensing images. A case study with Landsat ETM+ images is provided to demonstrate the implementation of the method and to allow checking of the programs.