Remote sensing

Remote sensing
See also: Weather radar
Twenty-four hour rainfall accumulation on the Val d'Irène radar in Eastern Canada. Zones without data in the east and southwest are caused by beam blocking from mountains. (Source: Environment Canada)

One of the main uses of weather radar is to be able to assess the amount of precipitations fallen over large basins for hydrological purposes.[88] For instance, river flood control, sewer management and dam construction are all areas where planners use rainfall accumulation data. Radar-derived rainfall estimates compliment surface station data which can be used for calibration. To produce radar accumulations, rain rates over a point are estimated by using the value of reflectivity data at individual grid points. A radar equation is then used, which is,

Z = ARb,

where Z represents the radar reflectivity, R represents the rainfall rate, and A and b are constants.[89] Satellite derived rainfall estimates use passive microwave instruments aboard polar orbiting as well as geostationary weather satellites to indirectly measure rainfall rates.[90] If one wants an accumulated rainfall over a time period, one has to add up all the accumulations from each grid box within the images during that time.




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