Editing Surface freshwater availability (section)

== Monitoring and Measurement ==
Monitoring surface freshwater availability involves a combination of remote sensing technologies, in situ hydrological measurements, and hydrological modeling. Satellite-based optical sensors are widely used to detect and quantify surface water extent and changes over time, leveraging spectral reflectance properties of water bodies. These observations are complemented by ground-based stream gauges, lake level measurements, and river discharge data collected by hydrological agencies.

Institutions such as [https://en.wikipedia.org/wiki/National_Aeronautics_and_Space_Administration NASA], [https://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administration NOAA], and various national hydrological services contribute to data acquisition and analysis. Advances in remote sensing have enhanced the capacity to monitor surface water dynamics at high spatial and temporal resolutions, enabling near-real-time assessments and long-term trend analysis. Hydrological models integrate observational data to estimate accessible surface freshwater volumes and support water resource evaluations.

Within the SIGNAL system, this phenomenon is treated as a defined environmental signal whose boundaries and measurement conventions are described below.