Estimation of ionospheric layer heights and velocities using available DRM signals

The spectrum time `waterfall´ of a received DRM (Digital Radio Mondiale) signal contains information about the ionosphere around the half-way point of the path between transmitter and receiver. Typical DRM signals have a flat-topped spectrum that is 9kHz or 10kHz wide. The most easily observed patterns in the spectra are caused by multipath interference mainly between one-hop and two-hop paths. The path difference is then a maximum of twice the effective layer height and a minimum of 87% of this. Half the path difference and hence the approximate layer height in km is 15 times the number of cycles of the interference pattern observed in a 10 kHz Bandwidth. Layer and aircraft reflection velocities can also be extracted from the DRM signal `waterfall´. “DRM Passive ionospheric Sounding, or DPS” is shown to be feasible.