The interferometers aboard the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) platforms use microwave technology to provide extremely precise measurements of the distance between the twin satellites in each mission. These measurements are then used to derive detailed estimates of Earth's gravity field. Such measurements are useful for tracking the movement of water around the planet, including underground water storage, the amount of water in large lakes and rivers, soil moisture, ice sheets and glaciers, and sea level.