This study describes a method to deduce the ionization layer virtual height and propagation path geometry responsible for communication between two HF radio stations a fixed distance apart. The method measures the Time Difference of Arrival (TDOA) between multipath propagation modes involving the active ionospheric layers and reconciles the data with a virtual height model of the ionosphere. The TDOA approach was implemented by transmitting audio signals that are sensitive to a time delay when summed together as happens in a receiver during multipath reception. The TDOA method eliminates the need for any absolute time references or extensive equipment calibration that would be required for an absolute time of flight (TOF) measurement. The audio waveforms used by the method included 1-cycle audio bursts, linear audio chirps of controlled sweep rate, and pseudorandom noise (PN) bursts.
Cerwin et al. (Fri,) studied this question.