Public defence in Space Science and Technology, Lic.Sc.(Tech.) Christer Holmlund

The title of the thesis: Control electronics for tuneable Fabry-Perot interferometers in hyperspectral imagers

Thesis defender: Christer Holmlund
Opponent: Prof. Tapio Fabritius, University of Oulu, Finland
Custos: Prof. Jaan Praks, Aalto University School of Electrical Engineering

Hyperspectral imaging has been rapidly evolving over 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 allows for identifying and analysing materials and substances based on their spectral characteristics. Hyperspectral imagers, or cameras, have been employed in satellites for various applications, including environmental monitoring, atmospheric studies, and solar and astronomic research. 

A tunable Fabry-Perot interferometer can be used as a scanning optical bandpass filter in a spectral imager. The wavelengths transmitted depend on the distance between the mirrors of the interferometer. The mirror gap must be controlled with sub-nanometre precision to achieve the required spectral stability and repeatability. The performance of the interferometer needs to remain consistent 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 in the ultraviolet channel of 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. 

Key words: hyperspectral imaging, Fabry-Perot interferometer, electronics

Thesis available for public display 10 days prior to the defence at Aaltodoc.