Investigation of target altitude estimation in skywave OTH radar using a high-resolution ionospheric sounder

This paper presents selected results from a novel ionospheric sounding experiment aimed at exploring the multipath propagation effect that is the basis for target altitude estimation in skywave OTH radar. To date the multipath propagation models that underpin altitude estimation algorithms have not been experimentally validated and it is believed that this accounts for instances of poor algorithm performance. As a first step in remedying this situation, measurements were made of the oblique skywave propagation channel between an OTH radar and an aircraft target at altitude over the sea. This experiment was conducted using an aircraft-borne transmitter and a ground-based HF sounder receiver. Resulting high resolution oblique ionograms are presented which demonstrate E-mode range-resolved altitude multipath. Examples are shown where raw ionogram data is processed to successfully estimate the aircraft altitude by using a simple E-mode multipath propagation model.