How The Measurement System Works
10
H|0|process|measurements|81|92|
H|0|alt|altimeter|63|71|
H|0|locate|precise orbit determination|676|702|
H|0|goals|mission objective|849|865|
G|0|ssh|sea-surface height|97|114|
G|0|1336km|1336 kilometers|201|215|
G|0|inc|inclination|239|249|
G|0|3_4cm|three or four centimeters|754|778|
G|0|topo|topographic|897|907|
G|0|precision|precision|47|55|
    The TOPEX/Poseidon spacecraft uses a high-precision radar altimeter to take measurements of sea-surface height over 90% of the world's ice-free oceans. 
    The satellite orbits at an altitude of 1336 kilometers above the earth at an inclination of 66 degrees. One revolution around the planet is referred to as an orbit. In approximately 10 days TOPEX/Poseidon completes 127 orbits, or a cycle. In that time it records sea-level measurements for the entire globe. 
    TOPEX/Poseidon measures the distance from the satellite to the sea surface to within approximately two and a half centimeters, about the diameter of a quarter. Scientists combine this measurement with precise orbit determination, allowing them to locate the spacecraft to within three or four centimeters. 
    These measurements allow TOPEX/Poseidon to achieve its primary mission objective -- the production of accurate topographic maps of all the world's oceans.
