Rain gauge
A rain gauge (also known as udometer, pluviometer, ombrometer, and hyetometer) is an instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation in a predefined area, over a set period of time.
[1] It is used to determine the depth of precipitation (usually in mm) that occurs over a unit area and measure rainfall amount.
[6][7] In 1441, the Cheugugi was invented during the reign of Sejong the Great of the Joseon Dynasty of Korea as the first standardized rain gauge.
[8][9][10] In 1662, Christopher Wren created the first tipping-bucket rain gauge in Britain in collaboration with Robert Hooke.
Richard Towneley was the first to make systematic rainfall measurements over a period of 15 years from 1677 to 1694, publishing his records in the Philosophical Transactions of the Royal Society.
So successful was he in this endeavour that by 1866 he was able to show results that gave a fair representation of the distribution of rainfall and the number of recorders gradually increased until the last volume of British Rainfall which he lived to edit, for 1899, contained figures from 3,528 stations — 2,894 in England and Wales, 446 in Scotland, and 188 in Ireland.
The results of these experiments led to the progressive adoption of the well-known standard gauge, still used by the UK Meteorological Office today, namely, one made of "... copper, with a five-inch funnel having its brass rim one foot above the ground ..."[15] Most modern rain gauges generally measure the precipitation in millimetres in height collected during a certain period, equivalent to litres per square metre.
In most cases the precipitation is not retained, but some stations do submit rainfall and snowfall for testing, which is done to obtain levels of pollutants.
Attempting to collect rain data in a tropical cyclone can be nearly impossible and unreliable (even if the equipment survives) due to wind extremes.
For virtually any gauge, drops will stick to the sides or funnel of the collecting device, such that amounts are very slightly underestimated, and those of .01 inches or .25 mm may be recorded as a "trace".
To alleviate this, a gauge may be equipped with an automatic electric heater to keep its moisture-collecting surfaces and sensor slightly above freezing.
This height is recorded with a pen that moves vertically, driven by a buoy, marking on the paper the rainfall over time.
Certain models measure the mass using a pen on a rotating drum, or by using a vibrating wire attached to a data logger.
The tipping bucket rain gauge consists of a funnel that collects and channels the precipitation into a small seesaw-like container.
After a pre-set amount of precipitation falls, the lever tips, dumping the collected water and sending an electrical signal.
An old-style recording device may consist of a pen mounted on an arm attached to a geared wheel that moves once with each signal sent from the collector.
In this design, as the wheel turns the pen arm moves either up or down leaving a trace on the graph and at the same time making a loud "click".
To measure the water equivalent of frozen precipitation, a tipping bucket may be heated to melt any ice and snow that is caught in its funnel.
Many Automated Surface Observing System (ASOS) units use heated tipping buckets to measure precipitation.
Acoustic disdrometers, also referred to as hydrophones, are able to sense the sound signatures for each drop size as rain strikes a water surface within the gauge.
