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Rain measurement: Difference between revisions
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== Optical Rain Gauge ==
These have a row of collection funnels. In an enclosed space below each funnel is a [http://en.wikipedia.org/wiki/Laser_diode laser diode] and a [http://en.wikipedia.org/wiki/Photodiode phototransistor detector]. When enough water has been collected to form a single drop it drips from the bottom of the funnel, falling into the laser beam's path. The detector is set at right angles to the path of the laser beam so that light scattered by the drop of water breaking the laser beam is detected as a sudden flash of light. The flashes from these photodetectors are then read and transmitted or recorded.
=Rain Gauge Location=
The exposure of a rain gauge is very important for obtaining accurate measurements. As a general rule, the windier the gauge location is, the greater the precipitation error will be.
Gauges should not be located close to isolated obstructions such as trees or buildings, which may deflect precipitation due to erratic turbulence.
To avoid wind and resulting turbulence problems, do not locate gauges in wide-open spaces or on elevated sites, such as the tops of buildings.
The best site for a gauge is one in which it is protected in all directions, such as in an opening in a grove of trees. The height of the protection should not exceed twice its distance from the gauge.
=Rain Rate=
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