Polar region ionosphere effects on UHF radar track acquisition

It is well known that small-scale variations in electron density in the natural ionosphere can disturb electromagnetic signals. These electron-density irregularities can cause rapid variations in the amplitude and phase of propagating signals, referred to as scintillation. UHF radars that operate in the polar region can experience scintillation anytime of the day or night. The occurrence of polar region scintillation is a complicated function of the physics of the ionosphere and the geometry of the line of sight. The severity of the scintillation is a strong function of time in the 11 year solar cycle and the geomagnetic activity (as quantified by K sub(p)). This paper considers the detection performance during track acquisition of UHF radars that must perform a wide-volume search while operating during various levels of scintillation disturbance that are likely to occur during the 11 year solar cycle. Under conditions of strong fading, ionospheric scintillation is the primary source of amplitude and phase variations, dominating the effect of target radar cross section fluctuations. The impact on the performance of the commonly used two-step sequential detection process for track acquisition can be improved by considering ionospheric scintillation in the radar design. The cost of ignoring ionospheric scintillation in the design process is demonstrated through examples. In the examples the design parameters for a two-step sequential detector are found using a constrained optimization procedure for cases with and without ionospheric scintillation. Cases are also shown where mismatched (to the prevailing ionospheric conditions) parameter sets are used instead of the optimal parameters.