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RAINGAUGE
GENERAL

The ordinary raingauge used for daily readings usually takes the form of a collector above a funnel leading into a receiver. The size of the opening of the collector is not really important, but an area of 200cm² to 1000cm² will probably be found convenient.

Raingauges for use at places where only weekly or monthly readings are taken should be similar in design to the type used for daily measurement, but with a receiver of larger capacity and stronger construction

Storage gauges are used to measured total seasonal precipitation. These gauges consist of a collector above a funnel, leading into a receiver large enough to store the seasonal catch.
 

MEASUREMENT SPECIFICATIONS

Two methods are commonly used for measuring the precipitation caught in the gauge : a graduated measuring cylinder, and a graduated dip rod. A measuring cylinder should be made of clear glass with a low coefficient of expansion and should be clearly marked with the size of gauge for which it is to be used. Its diameter should not be more than about one-third of that of the rim of the gauge.

The graduations should be finely engraved. In general, markings should be at 0.2 millimetre intervals with whole millimetre lines clearly indicated.
 

CONDITIONS OF USE

All gauges in any area or country should have comparable exposures, and the same siting criteria should be applied to all. The gauge should be exposed with its orifice being horizontal over ground level. The height of the gauge orifice above the ground should be as low as possible because the wind velocity increases with height, but it should be high enough to prevent splash from the ground. A standard height of one metre is recommended.

When adequate conditions from the wind is not possible, individual objects should not be closer to the gauge than a distance equal to four times their height.
 

TECHNICAL SPECIFICATIONS

Ring collector with a sharp edge linked to a cone-shaped funnel with a sufficient slope to avoid splashing effects.
Opening area : 200cm² to 1000cm²
Direct reading
Related graduate glass
Support stand for 1 meter elevation of the ring collector above ground level
Metallic or plastic made