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A back course marker (BC) normally indicates the ILS back-course final-approach fix where approach descent is commenced. It is identified by pairs of Morse-code "dots" at 3000 Hz (95 pairs per minute), which will trigger the white light on a marker beacon indicator, but with a different audio rhythm from an inner marker or en-route marker. [5]
Historically the first projection, invented by Marinus of Tyre ca. AD 100 according to Ptolemy, was what is now called equirectangular projection (historically called plane chart, plate carrée, Portuguese: carta plana quadrada). While it is very convenient for small seas like the Aegean, it is unsuitable for seas larger than Mediterranean or ...
The height of a benchmark is calculated relative to the heights of nearby benchmarks in a network extending from a fundamental benchmark. A fundamental benchmark is a point with a precisely known relationship to the vertical datum of the area, typically mean sea level. The position and height of each benchmark are shown on large-scale maps.
A non-directional beacon (NDB) or non-directional radio beacon is a radio beacon which does not include inherent directional information. Radio beacons are radio transmitters at a known location, used as an aviation or marine navigational aid .
Lead marks (as in "leading a ship into a safe place") and lights are fixed markers that are laterally displaced to allow a mariner to navigate a fixed channel along the preferred route. They are also known as "channel markers". [14] [failed verification] They can normally be used coming into and out of the channel. When lit, they are also ...
The beacon sits on Apple Orchard Mountain (4200 feet above sea level), a mountain along the Blueridge Parkway in Maidenhead grid square FM07fm, near Bedford, Virginia. Because there is no amateur band on 70 MHz in the United States, the beacon runs 24 hours a day under a non-amateur experimental license.
NAVD 88 was established in 1991 by the minimum-constraint adjustment of geodetic leveling observations in Canada, the United States, and Mexico.It held fixed the height of the primary tide gauge benchmark, referenced to the International Great Lakes Datum of 1985 local mean sea level (MSL) height value, at Rimouski, Quebec, Canada.
In low-lying or flat areas some trig points are only a few metres above sea level and one is even at −1 m (near Little Ouse, Cambridgeshire, TL61718 89787). [7] When all the trig points were in place, it was possible in clear weather to see at least two other trig points from any one trig point, but subsequent vegetation growth means that ...