Since Ferrell (1951) first reported anomalous VHF propagation in equatorial regions, a number of workers have observed the phenomenon during the early afternoon and evening hours, especially the latter. Backscatter experiments in the neighbourhood of the Virgin Islands were carried out by Villard, Stein, and Yeh (1957) employing fixed-frequency radar sounders located at St. Croix and by Dueno (1960) from Mayagiiez. Villard, Stein, and Yeh observed backscatter signals,. at frequencies up to 46� 2 Mc/s, corresponding to slant ranges up to 8000 km between 1500 and 2100 hr local time. These results were attributed to successive reflections from a tilted F layer without intermediate ground reflections (n F propagation). Dueno investigated the long-range trans-equatorial (LRTE) echoes at frequencies up to 49�68 Mc/s over a two-year period. He found a marked seasonal variation in the occurrence, the maxima occurring during the equinoctial periods. Low angle of arrival of the signals was deduced.
Long-range navigation for resource-constrained planetary rovers using angle of arrival