Across track scanners, known as whiskbroom electromechanical scanners, are multispectral imaging systems building the final image (ground cell by ground cell) by combination of the platform motion along the orbital track with a mechanical rotation of the collecting optic in the across track direction. Opto-mechanical are typically multi-spectral radiometers (no limitation on bands), whiskbroom systems are usually CDD spectrometers (high spectral resolution but just up to 1 micrometer). Examples of the sensors: Landsat Multispectral Scanner (MSS), Landsat Thematic Mapper (TM).