Investigations of ionospheric drifts
Since January 2004 Digisonde DPS4 provides routine ionospheric F-region drift measurements in the Průhonice Observatory (typically with 15 minutes sampling rate). Ionogram autoscaling process “ARTIST” automatically finds the F-region critical frequency foF2, from which convenient sounding frequencies are calculated for F-region drift measurements – autodrift regime.
Since May 2005, the Pruhonice Digisonde also measures E-region drifts every 15 minutes, using four fixed frequencies between 2.0 and 2.6 MHz. On the contrary to the autodrift setting, E region sounding frequencies do not depend on critical frequency: they are set and fixed for all the measurements. During summer 2006 the first special campaign for monitoring drifts in Es layer was performed. Drift-measurement on a higher sounding-frequency window 3.2-4.7 MHz was run every 15 minutes in addition to the standard E-region drift measurement. E-region drift measurement with two frequency-window setting represent an important source of information about the dynamics of the E region ionosphere and bring new pieces of information about sporadic E layer formation and its behavior. Differences of the plasma motion confirm different dynamics of E and Es layers.
We included a newly developed quality control - skymap point selection method (Kouba et al., 2008) to plasma drift evaluation. The method consists of a three-step selection of skymap points: (i) robust height range selection, (ii) setting limits on the Doppler frequency shift, and (iii) setting limits on the echo arrival angle. This selection method guarantees a better quality of obtained drift velocities.