Suboceanic Geodetic Measurements

This paper reviews the needs for geodetic ties among seafloor points and between such points and others on land, as well as the environmental constraints on potential systems for making such measurements. Underwater acoustic techniques provide the best opportunities, and an essential element on which to build acoustic systems-a precision-transponder system capable of making travel-time measurements over ranges of several kilometers with an accuracy of a few microseconds-is described. Finally, three particular systems are discussed. One uses direct transmission between transponders to achieve one part in 105 accuracy over ranges from a few meters to about a kilometer. The second, using a larger transponder network and an intermediate vehicle, can achieve similar accuracy over ranges up to about 10 km. The third is a composite acoustic global positioning system (GPS) which should be able to achieve subdecimeter accuracy over ranges of a few hundred kilometers.