Global Sea Level Observing System
Established in 1985, The Global Sea Level Observing System (GLOSS) is an Intergovernmental Oceanographic Commission (IOC) program whose purpose is to measure sea level globally for long-term climate change studies. The program's purpose has changed since the 2004 Indian Ocean earthquake and the program now collects real time measurements of sea level.
Source: Wikipedia — Global Sea Level Observing System (CC BY-SA 4.0)