Backscatter Ionospheric Sounding by a Continuous Chirp Signal

A spatially distributed chirp ionosonde records signals scattered by the Earth’s surface at long distances from the emitter, even with relatively low transmitter powers. Experimental studies of the ionosphere backscatter sounding (BS) based on the multifunctional chirp ionosonde developed at the Institute of Solar–Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS) have revealed the potential of such systems for diagnosing the propagation medium. With a transmitter power of a few kilowatts, it is possible to obtain high-quality BS ionograms within the maximum single-hop range (3000–4000 km). For the analysis of experimental data, algorithms for calculating the characteristics of BS signals, including the amplitude sweep of the recorded signal, are developed. Methods for diagnosing the decameter radio channel using BS data, which are based on the extraction of the leading edge of the BS signal during the processing and interpretation of ionograms, are elaborated. The results of extraction of the signal leading edge on the ionogram are used to calculate the maximum usable frequencies and characteristics of the oblique propagation trajectories for given radio paths in the sounding sector. Algorithms for inversion of the leading edge of the BS signal into the electron density are implemented.