Time variations of polarisation characteristics of HF radio signals during vertical and near-vertical incedence sounding of the ionosphere

The paper describes the equipment of the monostatic chirp ionosonde “Ionosonde-MS” upgraded in order to perform routine polarization measurements during vertical incidence and near-vertical incidence sounding of the mid-latitude ionosphere over the Asian part of Russia using a continuous chirp signal. Data of two-channel coherent measurements during registration of chirp signals exemplify time scales of the changes in ellipticity coefficient of reflected signals in vertical and near-vertical ionosphere sounding. A method is offered to control the possible impact of interference of scattered radio signals on polarization characteristics of ordinary and extraordinary waves using the amplitude measurements in a frequent mode.