1. A method for processing remotely acquired imagery, comprising: obtaining imagery data defining a first image of a panchromatic image type using a sensor characterized by a panchromatic spectral response curve, said first image having a first spatial resolution and a first spectral resolution; obtaining imagery data defining a second image of a multi-spectral image type using at least one other sensor characterized by a plurality of multi-spectral response curves associated with a plurality of optical bands, said second image having a second spatial resolution lower than said first spatial resolution and a second spectral resolution higher than that first spectral resolution; based on meta-data associated with at least one of said first and said second image, deriving a radiation transfer model; and determining a set of spectral weights for down-sampling said second image to said first spectral resolution based on said radiation transfer model and said panchromatic and said multi-spectral response curves.