Sea Level Change

This chapter describes the current ability of satellite altimetry for precisely measuring long-term sea-level variations, identifies limitations, and suggests future improvements. Satellite altimetry provides a means of overcoming the limitations of tide-gauge measurements because the measurements are truly global in distribution and tied to the earth's center-of-mass in a well-defined reference frame defined by the satellite tracking stations, in combination with other precise geodetic techniques. However, satellite altimetry is subject to its own unique set of errors, such as satellite orbit errors, errors in computing the atmospheric delay and sea-state corrections, and instrument errors. For many years, these errors severely limited the analysis of long-term changes in sea level using satellite altimetry, and T/P was the first mission with sufficient accuracy to allow real changes in mean sea level to be detected. A series of T/P-Jason-class satellite-altimeter missions should be able to measure the long-term rate of sea-level rise with about a decade of measurements, provided the instruments are precisely monitored using global positioning system (GPS)-positioned tide gauges.