Removal of Directwave High Frequency Signal for Ionospheric Sounder Return Processing: 11,047,967

A method of operating a vertical incidence sounder. The sounder transmits a random modulated sounder signal, and receives a return signal, comprising a directwave component and a reflected component. A first cross-ambiguity process between the transmitted signal and the return signal is used to time and frequency align the return signal with the transmitted signal. The direct wave signal is removed, thereby producing a processed return signal. A second cross-ambiguity process between the transmitted signal and the processed return signal is performed to determine a time offset, which is used to estimate an ionospheric height.