TIME, FREQUENCY AND SPACE GEODESY - IMPACT ON THE STUDY OF CLIMATE AND GLOBAL CHANGE

The science of time and frequency metrology has enabled the development of space geodetic systems that are being applied to the high accuracy tracking of new space-based instruments that have begun one of the most important investigations of the Earth ever undertaken. The accumulation of anthrogenic gases in the Earth's atmosphere, especially carbon dioxide, is likely to lead to global atmospheric warming. Warming may alter atmospheric circulation, rainfall patterns, and the melting of polar ice caps, which will cause sea level rise and pose a threat to our survival unprecedented in all of recorded history. 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 question is whether sea level is actually rising, and if so, at what rate? There are a wide variety competing instrument related artifacts and "geophysical signals" in the land and ocean data, all of which must be measured, modeled and removed before sea level signal can be completely distinguished. 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). Without the developments of these time and frequency technologies, none of these space geodetic methods would be possible.