Steve Cerwin and an international group of co-authors, from the University of Scranton, SSI and SERENE (Space Environment Radio Engineering Group, University of Birmingham) published "HamSCI HF multipath propagation mode analysis using amateur radios and audio waveforms sensitive to time difference of arrival" in Frontiers in Astronomy and Space Sciences.
Their 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.