Hydrologic remote sensing is a research field and methodological approach focused on the acquisition, processing, and analysis of data collected by sensors distant from the Earth's surface to study the distribution, dynamics, and properties of water across terrestrial and atmospheric systems. It enables the non-contact measurement and monitoring of diverse hydrological variables, including precipitation, soil moisture, snow and ice extent/properties, surface water bodies, groundwater storage changes, and evapotranspiration, utilizing various spectral bands (optical, thermal, microwave) and other signals (e.g., gravity). This capability is critical for understanding global and regional water cycles, supporting hydrological modeling, and informing water resource management, particularly over large or inaccessible areas.