The automatic rain gauge (pictured below right) is used to
not only measure the rainfall but also to determine its intensity and duration
(as depicted by the various hyetographs). This gauge is situated in short grass
adjacent to the MK 1A rain gauge shown opposite and the rim set similarly at
twelve inches above ground level. Rainfall is measured by an infra-red optical
sensor as it passes through the gauge, the resultant electronic signals being
sent via an underground cable to a remote datalogger which in turn is
connected to a PC for download and display functions. The datalogger is set to
record the rainfall at 5 minute intervals (but other time intervals could be
chosen). Sensitivity of the gauge is 0.01 mm which enables it to double up as a
dew gauge also! Data is downloaded to the PC daily and converted from raw
data to text files, and exported to spreadsheets
These photographs show the instruments used to measure rainfall
at Royston (Iceni) Weather Station. The instrument above is the M O Mk 1A
rain gauge which is checked daily at 0900 GMT and any collected rainfall
measured (see picture below for an 'exploded' view of this gauge). The gauge
is fixed firmly in the ground to withstand movement by the wind, and the brass
rim of the funnel set at the standard twelve inches above ground level. A deep
funnel is employed to prevent splashing of rainfall out of the gauge, and also to
hold snow for melting and conversion to water at the observation hour for
measurement. The rain gauge is set in short grass to minimise the risk of
rainfall splashing off the surface into the gauge.To the left of the gauge can be
seen the 30 cm earth thermometer, and behind the gauge the framework
supporting the Stevenson Screen
The Mk 1A rain gauge in pieces! Here the gauge has been
dismantled and various components laid out for the purposes of this
photograph and explanation. The copper outer cylinder is the only fixed
component and is shown here in its permanent position. (The paving slab
behind the gauge is sited far enough away from it so as not to present a danger
of rainfall splashing from the slab and into the gauge, but near enough for the
observer to be able to service the gauge daily without creating a bare patch in
the grass!). The glass collecting bottle is housed inside the copper inner
cylinder which is itself placed in the fixed outer cylinder. The copper funnel
(here shown inverted) is placed is slotted over the top of the outer cylinder and
firmly held there. In the event of the glass bottle overflowing (it has never yet
done so in a 24 hour period at Royston (Iceni) Weather Station) the additional
rainfall would be collected in the inner cylinder. Each day at 0900 GMT the
gauge is taken apart and the glass bottle taken out. Any rainfall collected in the
preceding 24 hour period is tipped into the measuring glass (again shown
inverted here) which is graduated to 10 millimetres. The measuring glass has a
pointed base to facilitate the measurement of very small quantities of rainfall.
Rain Gauge - Daily Precipitation
1. Standard Rain Gauge
A Standard Rain Gauge (SRG) is a gauge that collect precipitation in a hollow
metal tube with an open top. The opening at the top is 8 inches in diameter,
the reason the SRG is sometimes also known as an "8 inch gauge". Place in a
stand, the top of the gauge is about 3 feet high. During warmer months, a
smaller tube (2 inches in diameter) is placed inside the larger 8 inch tube. A
funnel fits on top so that the rainfall channels through the larger 8 inch
opening into the smaller 2 inch diameter tube. This allows the rainfall to be
measured more accurately in smaller increments. The observer uses a normal
ruler to measure the depth of the water in the small tube. In the winter, the
funnel and smaller tube are removed. This allows snow to fall directly into the
larger 8 inch tube. The snow is melted, then poured into the smaller 2 inch
diameter tube for measurement of the liquid equivalent.
Standard Rain Guage
1. Rain Gauges - Hourly Precipitation
1. Fischer Porter Rain Gauge
Sites reporting hourly
precipitation are most likely
equipped with a Fischer
Porter automatic rain gauge,
a white and cone-shaped
gauge resembling a rocket.
It stands about 5 feet tall
and 2 feet in diameter. This
gauge collects all types of
precipitation through a hole
in the top. Precipitation is
continuously collected in a
bucket on the inside. As the
bucket grows heavier, the
weight of the bucket presses
down on a scale. Every 15
minutes, a "ticker tape" is
punched with holes
according to the weight of
the bucket. The reading on
the tape keeps a running
tally of the amount of rainfall
and snowfall (in inches,
tenths, and hundredths) that
has occurred since the last
time the bucket was
emptied.
Fischer Porter Rain Gauge
Electronic Rain Gauges
Would you like to keep a history of the rainfall? An electronic rain gauge may be just
what you're looking for! All of the rain gauges we carry feature self-tipping collection
buckets. The accumulated rainfall accumulated is displayed on a convenient digital
display.