Numerous active experiments have been performed in association with Demeter. They are mainly related to ionospheric heating at high latitudes with powerful transmitters as HIPAS and HAARP in Alaska (Platino et al., 2006), Sura in Russia, and EISCAT in Norway (Tromsoe). A carrier wave at a frequency of several MHz is emitted with a modulation to change the ionospheric conductivity by heating. The current of the polar electrojet is then modulated and produces waves in the ELF/VLF range (Figures 34 et 35). These experiments allow to study the wave propagation and their effects on the radiation belts. Another experiment was also done in Ukrainia to study the propagation of an acoustic wave up to the satellite altitude.