Beware of per-pixel characterization of land cover

A simulation experiment was carried out to analyse the effects of the modulation transfer function on our ability to estimate the proportions of land cover within a pixel by linear mixture modelling. In the simulated landscape the proportion of each land cover type in every pixel was known exactly. The standard error of the estimate (SEE) between percentages derived from mixture modelling and the actual land cover percentages was 11%. Substantial improvements in estimating the percentages can be obtained simply by deriving estimates for pixels of twice the original dimensions, the SEE dropping to 4.16%, though this is with the obvious consequence of a final product with a coarser spatial resolution. Alternatively by deconvolving the input bands using a linear approximation of the point spread function the SEE can be reduced by almost as much, namely to 5.11%. If we combine the two approaches, by first doconvolving the bands, estimating the percentages and then aggregating resultant pixels to twice their original linear dimensions, the SEE drops to 2.24%.