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Unique observation and analysis of gravity wave (GW) propagation in the ionosphere was performed on the basis of multipoint and multifrequency continuous Doppler sounding in the Czech Republic. The sounding radio waves of various frequencies reflect at different heights. Thus, the propagation of GWs can be studied in three-dimensional space using the time (phase) delays between observation of corresponding signatures at different reflection points that are separated both horizontally and vertically. The individual reflection points correspond to different sounding paths (transmitter-receiver pairs) and are usually at heights between similar to 150 and similar to 260 km, depending on ionospheric conditions. It is shown that the wave vectors of the observed GWs were mostly directed obliquely downward, which means that the energy propagated obliquely upward. It was observed that energy of GWs decreased with height in the upper atmosphere. The observed average attenuation was around 0.14 dB/km.

Plain Language Summary Atmospheric gravity waves (GWs) represent an important wave mode that propagates at periods longer than about 5 min; they couple lower and upper atmosphere and influence the dynamics of the region in which they dissipate and cause perturbations in the ionosphere, which influences propagation of electromagnetic waves. This paper presents unique three-dimensional observations and analysis of GWs in the ionosphere at heights around 200 km. It shows that phase velocity vector of the observed GWs was usually directed obliquely downward, which means oblique upward propagation of energy. At the same time, the attenuation of GWs was observed; their energy decreased with increasing height. Azimuth of propagation changed and exhibited a seasonal dependence.