Super resolution: quincunx sampling and fusion processing

In order to increase SPOT5 panchromatic resolution, CNES adopted in 1995 a quincunx sampling mode named THR, which is a French acronym for "very high resolution". Such a sampling is produced by two CCD linear arrays shifted in the focal plane and has been shown to meet Shannon requirement at first order. That means a good fit between the sampling and the instrument modulation transfer function (MTF) and thus an optimization of the whole acquisition system. SPOT5 THR is a 2.5 m image obtained through a rather complex processing of the two 5 meter shifted images delivered by the double CCD linear array, consisting in quincunx interpolation, deconvolution and denoising. Quincunx interpolation computes radiometric information over a 2.5m grid while only half the information may be retrieved from the two 5m images, deconvolution compensates for low MTF values for high spatial frequencies and denoising reduces the noise level enhancement due to deconvolution. Apart from the high resolution panchromatic mode, SPOT5 also delivers classical 10m multispectral images covering the green, red and near infrared spectral domains that are almost simultaneously acquired. Merging the 2.5m THR with the 10m multispectral yields a 2.5m multispectral product which proved to be of utmost interest for thematic applications. Gathering the main results from the SPOT5 in orbit commissioning period, this paper gives an overview of THR and fusion processing, points out onboard and onground sensitive parameters and finally presents the THR and THX performances.