Control electronics for tuneable Fabry-Perot interferometers in hyperspectral imagers

Hyperspectral imaging has been rapidly evolving during the last decades. In hyperspectral imaging, a contiguous spectrum is acquired for each pixel in an image. Typically, a hyperspectral camera covers part of the wavelength range from the near ultraviolet to the mid-infrared in tens to hundreds of wavelength channels. This capability enables identifying and analysing materials and substances based on their spectral characteristics. Hyperspectral imagers or hyperspectral cameras have been used in satellites for various purposes, including environmental monitoring, atmospheric studies, and solar and astronomic research. A tuneable Fabry-Perot interferometer can be used as a scanning optical bandpass filter in a spectral imager. The transmitted wavelengths depend on the distance between the mirrors of the interferometer. In order to achieve the required spectral stability and repeatability, the mirror gap has to be controlled with sub-nanometre precision. The performance must remain unchanged over a wide operating temperature range. This thesis presents the control of the Fabry-Perot interferometers used in the hyperspectral imagers of the nanosatellites Aalto-1 and PICASSO. The electronics of the controller for the Fabry-Perot interferometers of the ultraviolet channel in the ALTIUS spectral imager are described in some detail. The ALTIUS instrument and satellite, currently under construction, are part of the European Space Agency’s Earth Watch programme.