Abbreviation for over-the-horizon radar, a type of radar originally developed to detect military targets far beyond the optical horizon Radio waves in the 5 to 28 MHz range are reflected from the ionosphere and reach up to 3500 km in one hop Properties of the ocean surface are extracted from the energy backscattered from the ocean surface Properties that can be measured include surface wind direction, radial surface currents, sea state, surface wind speed, and more See the OTH Web site