THE METHOD OF ADJUSTING THE MULTI-FREQUENCY PROBING RADAR SIGNAL PARAMETERS AND THE TROPOSPHERIC RADIO WAVEGUIDE CHARACTERISTICS

Abstract

Peculiarities of air circulation in the coastal zone of large reservoirs (large lakes or inland seas such as the Black and Azov Seas) can lead to a significant departure from the standard spatial distribution of meteorological and, accordingly, radiophysical characteristics of air. As a result, it is possible for regions of space with an abnormally low attenuation level of radio waves of certain frequency ranges to appear – tropospheric radio waveguides (TWG). The appearance of TWG leads to multi-beam propagation of radio waves and fluctuations of radar signals. Fluctuations of the radar signal lead to a decrease in the range of detection of aerial objects by radars. For single-frequency radar signals, it is only possible to estimate the degree of distortion and the amount of radar detection range loss. A paradoxical situation arises when, due to TWG, it is possible to increase the range of detection of aerial objects, but due to the distortion of the radar signal in TWG, the detection performance decreases. For multi-frequency signals, it is potentially possible to adjust the parameters of the radar signal with the parameters of the radar channel (in this case, the tropospheric radio waveguide). The adjustable parameters of a multifrequency signal include: the number of frequency components; bandwidth of the frequency component; average frequency of the frequency component; signal duration; period. The characteristics of TWG, on which the parameters of the multifrequency signal depend, include: the lower transmission frequency of TWG; the upper transmission frequency of TWG; the delay time of the rays in the TWG. The bandwidth and beam delay values can be obtained directly by emitting and receiving a test multi- frequency pilot signal, but this method requires the presence of a reference reflector in space, which is difficult to implement in practice. The electrophysical characteristics of the tropospheric waveguide can be determined from the data of meteorological observations. The method developed in the article allows, based on the known characteristics of the tropospheric waveguide, to determine and adjust the parameters of a multi-frequency signal, which reduces the fluctuations of the sounding signal and increases the aerial objects detection rang.