A Self-Calibration O/X-Mode Separation Method for Ionosonde

Radio waves in the ionosphere propagate in two modes: ordinary (O) and extraordinary (X). Accurate parameter inversion necessitates their separation. This letter proposes a self-calibrating O/X-mode separation method. By focusing on the higher-frequency branches beyond the overlap point of the F2 layer O/X traces, a direct iterative optimization method is used to determine phase-shift and amplitude compensation parameters for mode synthesis. By tracking diurnal variation characteristics of ionograms and extrapolating predictions, the parameters across the whole frequency bands can be determined. Comparing with the traditional separation method, this method is independent of antenna type and alignment, requires no internal or external calibration source, and can provide real-time calibration updates.