Dynamic Effects in Gravimetry: An Assessment of the Current State of Knowledge

Technology for gravimetry and positioning are evolving, with major changes projected within the decade. These new technologies are anticipated to improve measurement accuracies such that: dynamic relative gravimeters would be accurate to < 1 milliGal; static relative gravimeters would be accurate to < 1 microGal; and static absolute gravimeters would be accurate to < 10 nanoGal. With instruments that are sensitive to signals several magnitudes smaller than currently possible, the question arises about which dynamic effects of the natural and manmade environments will affect these more sensitive instruments.

This talk will attempt to summarize the current state of knowledge on forces that produce dynamic gravity effects and dynamic forces that could affect the ability to make gravity measurements with new instrumentation at nanoGal levels. Some examples of processes that produce dynamic gravity signals include: earth and ocean tides, fluid withdrawal in the subsurface, atmospheric density changes, earthquakes, and glacial isostatic adjustment. A separate set of dynamic environmental factors affect the ability to make accurate gravity measurements, including: movement of humans or other mass near sensitive instruments, vibrations, vehicle motion for kinematic measurements, environmental forcing on field absolute gravimeters, etc. These effects will be considered for not only their magnitudes, but also their spatial scales (from continental to within the immediate vicinity of the gravity instrument) and their uncertainties. The goal of this work is to provide guidance on which dynamic gravity effects are well known and which are not, as well as what corrections may needed for future gravity measurements.