Time, frequency and space geodesy: impact on the study of climate and global change

The authors discuss the development of space geodetic systems-important tools in an attempt to understand the evolution of the atmosphere and oceans-particularly as they pertain to the problem of global warming. The science of time and frequency metrology has made possible the development of space geodetic systems that are being applied to the high accuracy tracking of new space-based instruments. These new instrument sets and methodologies have been designed to be appropriate for many years to decades of operation in order to measure the open ocean circulation and sea level as an indicator of global warming and will be a vital means for assessing the effectiveness of future remedial actions. The issues of time and frequency are tied into all of these space geodetic techniques, from the cesium and rubidium oscillators aboard global positioning system (GPS) satellites, to the epoch time and time interval measurements of satellite laser ranging (SLR) and hydrogen maser references used in very long baseline interferometry (VLBI)