In-flight commissioning of SPOT5 THR quincunx sampling mode
Christophe Latry, Bernard Rougé · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2003
In order to increase SPOT5 panchromatic resolution, CNES adopted in 1995 a quincunx sampling mode named THR: two CCD linear arrays shifted in the focal plane deliver two images shifted by 0.5 pixel. Such a sampling scheme has been shown to meet Shannon sampling requirement at first order, thus optimizing the whole system. Meeting Shannon requirement means blurred images, since the MTF has low values at Nyquist frequencies. This leads to a complex on ground THR processing chain, including three steps : quincunx interleaving/interpolation, deconvolution and denoising. The first two steps consist of convolutions which are realized in the Fourier domain but the third one uses a complex spatial-frequency analysis thanks to a wavelet packet decomposition. During the in-flight commissioning period which starts immediately after launch and spreads over two months, the best fitted THR processing chain parameters have been computed to assess the image quality of the final THR restored product. The goals of this paper is to present the principles of the THR sampling mode, to detail how the in-flight commissioning of SPOT5 THR mode has been realized and to present its conclusions.