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View of the ocean with two ships: one in the foreground and one to the left of it on the horizon. Historically, the distance to the visible horizon has long been vital to survival and successful navigation, especially at sea, because it determined an observer's maximum range of vision and thus of communication, with all the obvious consequences for safety and the transmission of information ...
A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. [2] [3] [4] Historically, it was defined as the meridian arc length corresponding to one minute ( 1 / 60 of a degree) of latitude at the equator, so that Earth's polar circumference is very near to 21,600 nautical miles (that is 60 minutes × 360 degrees).
With this calculation, the horizon for a radar at a 1-mile (1.6 km) altitude is 89-mile (143 km). The radar horizon with an antenna height of 75 feet (23 m) over the ocean is 10-mile (16 km). However, since the pressure and water vapor content of the atmosphere varies with height, the path used by the radar beam is refracted by the change in ...
The United States Navy created their own system, the AN/TPS-71 ROTHR (Relocatable Over-the-Horizon Radar), which covers a 64-degree wedge-shaped area at ranges from 500 to 1,600 nautical miles (925 to 3,000 km). ROTHR was originally intended to monitor ship and aircraft movement over the Pacific, and thus allow coordinated fleet movements well ...
If the height h is given in feet, and the distance d in statute miles, d ≈ 1.23 ⋅ h {\displaystyle d\approx 1.23\cdot {\sqrt {h}}} R is the radius of the Earth, h is the height of the ground station, H is the height of the air station d is the line of sight distance
It is impossible to determine longitude with an accuracy better than 10 nautical miles (19 km) by means of a noon sight without averaging techniques. A noon sight is called a Meridian Altitude. [ 2 ] While it is very easy to determine the observer's latitude at noon without knowing the exact time, longitude cannot accurately be measured at noon.
[2] [3] It is also close to the distance to the visible horizon as observed from sea level by a person about six feet tall, so is the limit of what is visible from land. Since the mid-20th century, numerous nations have claimed territorial waters well beyond the traditional three-mile limit.
Horizon distance graphs: Image title: Graphs of distances to the true horizon on Earth for a given height above sea level, h by CMG Lee. s is along the surface of the Earth, d is the straight line distance, and ~d is the approximate straight line distance assuming h << the radius of the Earth, 6371 km. In the SVG image, hover over a graph to ...