The research of backscatter ionosphere sounding features on the base of chirp ionosonde

We present the results of researches for backscatter ionosphere sounding (BS) on the basis of multipurpose chirp ionosonde developed in ISTP SB RAS. Points of transmitter (52.8°N, 103.3°E) and receiver (51.8°N, 103°) are located near the city of Irkutsk. In the BS mode given ionosonde can be treated as low-power systems, with a power of transmitter less than 1 kW, and allows registering scattered signals within the maximum range of one hop (~3000 ÷ 4000 km). The experimental data of BS sounding obtained during various seasons during 2005-2009 were analyzed. The saved-up data array allows investigating features of BS signals propagation in various heliogeophysical conditions. For the analysis and interpretation of BS signals on the ionograms we used the results of characteristics modeling for chirp signals under ionosphere backscatter and oblique sounding in the framework of waveguide approach. The most characteristic types of ionograms have been revealed and conditions of appearance of this or that type depending on time of day, season, sounding direction and medium condition are established. In the winter, in the spring and in the autumn the prevailing types are ionograms with BS signals corresponding to propagation mode by means of reflection from ionosphere F layer. The ionosphere condition characterized by this type of ionograms creates optimum conditions for a choice and adjustment of working frequencies for oblique sounding. As a rule, it is possible to receive qualitative ionograms for ranges up to 3000 + 4000 of km. In transitional hours of days along with the main signals one can register the signals coming from the directions opposite to the azimuth of radiation. During the summer periods the signals reflected by layers of E or Es are registered. At the same time frequencies of the received signals are sufficiently big and in some cases reflections from F layer are absent. This ionogram type allows evaluating illumination of the land surface at the distances which aren't exceeding 1500-2000 km. We also registered ionograms with non-standard traces of the reflections having weak frequency dependence on group way which can't be interpreted as standard BS signals.