5. Spectro-imagers operating in raster-scroll mode

Raster-scrolling instruments are very similar to tunable-filter spectro-imagers, since they are also built by inserting a spectral filter into a conventional imaging system. However, this filter is chosen so that each spectral characteristic to be measured (wavelength or step difference, in practice) is associated with a column of the detector. If we scroll the scene perpendicularly to these columns, each point of the object will be seen successively in all spectral states, and this is how we can reconstruct the spectrum of all the points in the scene whose image has entirely passed through the detector matrix. The operation of these devices therefore requires a scan of the scene similar to that required by linear-field instruments.