Recent advances in real-time analysis of ionograms and ionospheric drift measurements with digisondes

Reliable long distance RF communication and transionospheric radio links depend critically on space weather, and specifically ionospheric conditions. Modern ground-based ionosondes provide space weather parameters in real-time including the vertical electron density distribution up to similar to 1000 km and the velocity components of the ionospheric F region drift. A global network of digisondes distributes this information in real-time via internet connections. The quality of the automatic scaling of the echo traces in ionograms was a continuous concern ever since first attempts have been reported. The modern low-power ionosonde with similar to 100 W transmitters (compared to several kilowatt for the older ionosondes) relies on more sophisticated signal processing to enhance the signal-to-noise ratio and to retrieve the essential ionospheric characteristics. Recent advances in the automatic scaling algorithm ARTIST have significantly increased the reliability of the autoscaled data, making the data, in combination with models, more useful for ionospheric now-casting. Vertical and horizontal F region drift velocities are a new real-time output of the digisondes. The "ionosonde drift" is derived from the measured Doppler frequency shift and angle of arrival of ionospherically reflected HF echoes, a method similar to that used by coherent VHF and incoherent scatter radars. (c) 2005 Elsevier Ltd. All rights reserved.