Oblique Chirp Sounding and Prediction of the Maximum Usable Frequency on the Middle- and Long-Distance Paths

We present the results of experimental studies of the maximum observed frequency (MOF) variations in 2016–2019 on the middle- (Cyprus—Rostov-on-Don) and long-distance (Laverton—Rostov-on-Don) paths. The accuracy of prediction of the maximum usable frequency (MUF) when the ionosphere state is specified in terms of the IRI-2016 model with allowance for the global empirical model of the sporadic E s layer is estimated. It is shown that in a quiet geophysical environment, typical values of the relative r. m. s. deviation of the MUF from the MOF reach 9%. On a long-distance Laverton—Rostov-on-Don path, the IRI-2016 model gives significantly underestimated MUF values, and the relative r. m. s. deviation of the MUF from the MOF reaches 12%.