Remote sensing of the terrestrial environment with an HF radio high-resolution azimuth and elevation scan system

High-resolution arrays, steerable over a sector in azimuth and elevation, can be used to sense the state of the remote ionosphere and possibly certain characteristics of the sea surface. Direction-of-arrival measurements of one-way signals or backscatter techniques can sense the presence of traveling ionospheric disturbances and determine some of their parameters. Backscatter data can provide information on HF skip distances and ionospheric plasma frequencies at long distances. Spectrum analysis of sea scatter may provide some information on sea state. These uses are illustrated by several examples.