Orbit Determination and Sea Level Rise: How Astrodynamics Informs Us About the Climate

Abstract

Advancements in satellite tracking systems, Earth-gravity field models, and the definition of the terrestrial reference frame have led to significant improvements in the orbit determination for low Earth orbit satellites over the last few decades. These improvements have allowed climate-driven variations in the hydrosphere to be detected for the first time. The monitoring of global mean sea level variations was not originally a goal of satellite altimeter missions such as TOPEX/Poseidon, but now they are measured with an accuracy of ∼4 mm every 10 days because of improvements in the orbit determination (radial component ∼1 cm) and other advances. Similarly, satellite gravity missions such as GRACE have allowed time-variable gravity to become a major scientific objective, with monthly estimates of changes in global ocean mass with an accuracy of 2 mm. Taking advantage of these measurements for climate change studies will require multidecadal time-series using multiple satellite missions that may be tracked by different techniques and methods as technology evolves. For this reason, maintenance and improvement of the terrestrial reference frame is a critical component of an overall plan to monitor the Earth’s water reservoirs from space.