The application of geodetic radio interferometric surveying to the monitoring of sea-level

Abstract

Under project IRIS (International Radio lnterferometric Surveying) geodesists are using Very Long Baseline Interferometry (VLBI) to monitor polar motion to 1-2 ms of arc and UTl to 0.05-0.10 ms, and to develop a global geodynamic network to detect and study centimetre level displacements of reference points associated with large-scale phenomena such as tectonic plate motion and glacial rebound. Differential positioning techniques using the signals broadcast by the satellites of the Global Positioning System (GPS) are being used to study fiier scale phenomena, such as localized subsidence, and economically to relate these specialized surveys to the geodynamic network. Including tide gauge stations in this system will make it possible to detect motions of specific gauges and correct or delete the measurements from those gauges when computing changes in sea-level. The National Oceanic and Atmospheric Administration (NOAA) has selected several tide gauges on the east and west coasts of the United States, and initial epoch GPS surveys to tie the gauges to VLBI observations have already begun. Other countries participating in project IRIS are planning similar activities. In addition to providing a globally based land reference datum for the tide gauge measurements, the IRIS polar motion and UTl time series may contribute directly to monitoring and interpreting global sea level changes. Changes in the volume and distribution of ice masses result in longterm motions of the axis of rotation, and sea-level changes affect the length of day (lod). The IRIS time series will certainly have the resolution required to detect the expected polar motion and changes in lod, and a properly designed global VLBI/GPS network should allow the ice/sea-level effects to be separated from crustal dynamics effects.

The History of the Earth's Rotation: Impacts of Deep Earth Physics and Surface Climate Variability

“…This pattern is well understood to arise as a consequence of the interference between the 12-month periodic annual wobble and the $14-month periodic Chandler wobble that were discussed in Section 9.09.2 of this chapter. Most of these results are shown in Figure 16 where they are accompanied by an early result derived on the basis of the analysis of VLBI observations by Carter et al (1986). According to Dickman (1977), the true polar wander (TPW) evident as the secular drift of the position of the pole upon which the oscillatory signal is superimposed was occurring at a rate of (0.95 AE 0.15) My À1 along the 75.5 W meridian over this time period as shown in the inset polar projection in Figure 15.…”

Postglacial variations in the level of the sea: Implications for climate dynamics and solid‐Earth geophysics

“…The analysis of the data by Dickman [1977] has now also been performed by many others, and their results are all compiled on Figure 12b. Also shown on Figure 12b is the result of an additional measurement based upon VLBI data by Carter et al [1986]. Given this discussion of the main types of observational data that we intend to explain and explore, it will be most informative to next consider the theory that has been devised to make this possible.…”

Glacial isostatic adjustment and Earth rotation: Refined constraints on the viscosity of the deepest mantle

“…Induced by a wide variety of complex internal and external processes, observed changes in rotational state span a broad spectrum of timescales ranging from hours to millions of years. Of the very wide range of rotational variations that do occur, we refer to as "polar wander" the secular drift of the axis of rotation with respect photo-zenith tubes, has more recently been corroborated using very long baseline interferometry observations from the radio telescopes contributing to the International Earth Rotation Service [Carter et al, 1986].…”