Explore the versatile applications of GNSS geodesy in this 31-minute plenary talk from the JpGU-AGU 2020 conference. Delve into how a single observing system can measure crustal deformation, sea-level change, tropospheric water vapor, and ionospheric tsunamis. Learn about GPS basics, atmospheric effects, and reflected GPS signals. Discover the system's role in studying Earth systems, including slip distribution, seismic gaps, and ionospheric responses. Examine its use in monitoring sea level, snow depth, storm surges, soil moisture, drought, vegetation moisture, and volcano inflation. Gain insights from Emma Hill of the Earth Observatory of Singapore and Asian School of the Environment at NTU Singapore as she showcases the multifaceted capabilities of GNSS geodesy in environmental and geological research.