SATI image processing and mesopause temperature determination Original Research Article

The Spectral Airglow Temperature Imager (SATI) instrument registers airglow coming from an annular mesopause segment. The temperatures of various points of this segment are retrieved by sectors of the registered images containing spectral information. A stage of SATI spectrogram processing connected with deriving spectral information from images and the determination of the rotational temperature of oxygen molecules emitting at the altitude of the mesopause is considered. A “moving sector” approach for sector spectra calculation is proposed. Typical for this approach is the possibility for varying the number of calculated sector spectra from one image and the sector angle. The sector angle may be selected depending on the quality features of the images. Two versions, one based on averaging and a second – based on finding the median of the values of all pixels at equal distance from the image center are developed. The determination of a mean temperature based on a whole image mean spectrum is considered as a potential source of systematic and gross errors. A determination of the mean temperature by averaging sector temperatures is proposed. Applying criteria for evaluating the usability of sector temperatures based on azimuthal distribution of sector errors, emission intensities and backgrounds is possible. The moving sector approach is useful with the possibility for a detailed visual evaluation of the azimuthal distribution of retrieved sector variables – rotational temperature, emission rate, background and error.