Geodetic Observations and Global Reference Frame Contributions to Understanding Sea-Level Rise and Variability
Understanding Sea-Level Rise and Variability
Geodetic observations are necessary to characterize highly accurate spatial and temporal changes of the Earth system that relate to sea -level changes. Quantifying the long -term change in sea -level imposes stringent observation requirements that can only be addressed within the context of a stable, global reference system. This is absolutely necessary in order to meaningfully compare, with submillimeter accuracy, sea -level measurements today to measurements decades later. Geodetic
... s can provide the basis for a global reference frame with suffi cient accuracy. Signifi cantly, this reference frame can be extended to all regional and local studies in order to link multidisciplinary observations and ensure long -term consistency, precision, and accuracy. The reference frame becomes the foundation to connect observations in space and time and defi nes the framework in which global and regional observations of sea -level change can be understood and properly interpreted. Geodetic observations from in situ , airborne, and spaceborne platforms measure a variety of quantities with increas-ing accuracy and resolution and address interdisciplinary science problems, including global sea -level change. In this chapter we identify critical geodetic requirements to meet the rigorous scientifi c demands for understanding sealevel rise and its variability, and thus contribute to improving its prediction. In particular, we stress the need for the continuity of the geodetic observational series that serve basic research, applications, and operational needs. Geodesy: Science and Technology Geodesy is concerned with the measurements of geometry, Earth orientation, and gravity and the geoid. • Geometry: this refers to changes of the position of the Earth with respect to a system of quasars through time, and, in the context of sea level, changes of the surface geometry of the Earth; that is, the variations in time and space of ocean surfaces and ice covers, and of horizontal and vertical deformations of the solid Earth. Unfortunately, geodesy currently is not able to measure the vertical deformations of roughly 71% of the Earth ' s surface that is the ocean fl oor. • Earth orientation: this is measurement of fl uctuations in the orientation of our rotating planet relative to the stars, commonly divided into precession, nutation, polar motion, and changes in Earth rotation, which defi nes and monitors the transformation between the celestial (quasar system) and terrestrial (Earth -fi xed) reference frames. Earth rotation is described by the Euler -Liouville equations describing the motion of a rather general Earth, including the solid (non -rigid) body, oceans, and atmosphere.