Data are MATLAB files SO166GRAM_YYYYMMDD_hhss.mat containing one-minute data of the sounding
as a structure array with following fields:

    SCode: 'SO166' - code of the ionosonde
    SName: 'SODANKYLA, FINLAND' - name of the observatory
       TZ: 'UTC' - time is given in UTC
     clim: [20 110] - data limit, dB
      fft: 4096 - length of fft for the ionograms, see (Enell et al., 2016) for more details
      lat: 67.4 - Geographic latitude of the ionosonde
      lon: 26.6 - Geographic longitude of the ionosonde
     mode: 'O' - o-mode 
     time: [year montht day hour minute second]
    title: 'O-mode ionogram, Sodankyl (SO166, 67.4N, 26.6E), 2015-05-20, 08:09 UTC, FFT=4096'
     xlim: [0.52621 15.966] - Frequency range,MHz
     ylim: [2.8617 1502.4] - height range, km
     data: [525×590 double] - matrix, range x frequency
     
Reference:
Enell, C.-F., Kozlovsky, A., Turunen, T., Ulich, T., Välitalo, S., Scotto, C., and Pezzopane, M. (2016), 
Comparison between manual scaling and Autoscala automatic scaling applied to Sodankylä Geophysical Observatory ionograms, 
Geosci. Instrum. Method. Data Syst., 5, 53-64, 
doi:10.5194/gi-5-53-2016.