Between a rocky planet and a watery place: the problem of observing the solid Earth and hydrosphere together

Peter Clarke
University of Newcastle, U.K.

Comprehensive tracking of the water cycle remains a tricky problem, in part because water resources are spatially widely distributed and take many different forms (including oceans, snow, ice, lakes and rivers, soil moisture, ground water, and atmospheric water vapour), and in part because some of these forms are invisible or unconstrained by traditional measurements on the Earth's surface. Geodetic techniques offer the possibility of tracking all water mass movements, by observing one or more of (i) the change in Earth's gravitational field, (ii) the change in Earth's shape caused by the alteration in the surface mass load, and (iii) the variation in the Earth's rotation axis and rate caused by the change in its inertia tensor. However, these observations are also sensitive to changes with different causes, such as tectonics, glacio-isostatic adjustment, and other mass movements; furthermore, each technique has advantages and disadvantages resulting from its spatial/temporal sampling density and its susceptibility to random and systematic errors. This overview presentation will explore these issues, to set the scene for more detailed discussions during the workshop.