Geodesy goes high tech

Satellite-based geodesy has permitted measurements of the earth's shape and dimensions to an accuracy of 1 m on a global scale. VLBI techniques, using quasar signals recorded simultaneously by radiotelescopes situated around the globe, are permitting accuracies within 3-5 cm for polar motions, terrestrial rotational times as close as 0.1 msec, and distances between stations to within 1-2 cm. An operational constellation of 18 GPS satellites is expected to permit position measurements within 10 m, 24-hr per day. Relative locations between points will be measurable to within 1 cm, and moving locations, such as a truck, to within 10 cm. The recently observed several millimeter/year rise in the height of the Atlantic Ocean on the eastern shore of the U.S. requires continuous monitoring of the shoreline height, as well as the heights of the polar ice masses, which may be gradually melting due to the greenhouse effect. Sea surface geodesy would also possibly permit identification of incipient El Nino events and thus allow a choice of different crops to plant in South America to compensate for the weather anomalies to follow.