ABSTRACT
The objective of precipitation measurement is to determine the spatial and temporal distribution of precipitation, primarily rain and snow, but including all forms of precipitation. Measurement requirements depend on the scope and purpose of their use. For climatological and hydrological purposes, such as water supply assessment, precipitation measurement seeks to determine the amount of water that reaches the earth surface over a given area, usually for a 24-hr period with an area of 100 km2 or greater. For stormwater runoff and flash flood forecasting, precipitation amount and rate measurements are needed on a time scale of minutes to an hour for areas of tens of square kilometers. For microwave circuit design, rainfall rate along a narrow transmission path is needed on a time scale of a few minutes. Precipitation is usually measured with gages of various designs that meet specific needs over a wide range of geographic locations. Precipitation may also be indirectly measured or inferred with remote sensing technology with sensors operating in visible, infrared, microwave, or gamma ray portions of the electromagnetic spectrum. Remote sensing technology is beyond the scope of this report. A review of the measurement of precipitation is given in Ref.[1].
