Reshaping Earth: How the TOPEX and Jason satellites revolutionized oceanography and redefined climate science

Humans are reshaping the Earth. Not just the climate of Earth, but the planet itself. As the Earth warms due to human interference with the climate, the oceans absorb this extra heat and glaciers and ice sheets melt, causing the oceans to rise. Covering more than two thirds of the planet's surface, it means the rising oceans are literally changing the shape of the planet we call home. Since the early 1990s, a series of satellites (e.g., TOPEX-Poseidon, followed by Jason-1, Jason-2, and then Jason-3) has captured this change with remarkable accuracy. Built to measure changes in sea level, these satellites have revolutionized our understanding of the oceans, especially how the oceans store and redistribute heat around the planet, and now provide one of the most important records of how fast our climate is changing. The unprecedented success of these missions has led to the development of the Jason-CS/Sentinel-6 Mission, under a US-European collaboration, that will ensure another full decade of sea level observations. This mission includes two satellites launched 5 years apart, with the first satellite Sentinel-6 Michael Freilich launched in November 2020. In the beginning of the altimetry era, the largest uncertainties had to do with orbit determination, more recently things like radiometer stability have become important and perhaps the current and ongoing technical issues have more to do with increasing resolution and temporal sampling. This paper will summarize the history and evolution of the science, mission and technology development and programmatic mechanisms fueled by a global collaboration to achieve and sustain this crucial and unprecedented climate data record.