Table of Contents
What Is Rain Gauge?
A rain gauge is a meteorological instrument to measure the liquid precipitating in a given amount of time per unit area. It is also known as an udometer, pluviometer, or ombrometer.
We will discuss various types of rain gauges with schematic diagrams.
Types Of Rain Gauges
There are two types of Rain Gauges as classified below.
- Non-Recording Type Rain Gauge
- Recording Type Rain Gauges
Both types of rain gauges are described below.
1. Non-Recording Type Rain Gauge
Non-recording type rain gauge is the most common type of rain gauge used by the meteorological department. It comprises a cylindrical vessel 127 mm in diameter with a base enlarged to 210 mm diameter.
At its top section, the funnel is provided with a circular brass rim which is 127 mm exactly so that it can fit into the vessel wall. This funnel shank is inserted in the neck of a receiving bottle which is 75 to 100 mm high from the base section and thinner than the cylinder, placed into it to receive precipitation.
A Receiving bottle has a capacity of 100 mm and during heavy rainfall, the amount of rain is often exceeded, so the reading should be measured 3 to 4 times a day. Water contained in this receiving bottle is measured by a graduated measuring glass with an accuracy of up to 0. 1 mm. For uniformity, the rainfall is measured each day at 3:00 AM UTC and is recorded as rainfall of the day.
Proper care, maintenance, and investigation of rain gauge particularly during dry climate are necessary to keep the instrument free from dust and dirt so that the readings are precise.
2. Recording Type Rain Gauges
There are three types of recording rain gauges as follows
(I) Weighing bucket type
(II) Tipping bucket type
(III) Floating or natural syphon type rain gauge
(I) Weighing bucket type
Weighing bucket-type rain gauge is the most common self-recording rain gauge. It comprises a receiver bucket supported by a spring or lever balance or some other weighing mechanism. The movement of the bucket due to its increased weight is transmitted to a pen which traces record or some marking on a clock-driven chart.
The weighing bucket-type rain gauge instrument gives a plot of the accumulated rainfall values against the elapsed time and the curve so formed is called the mass curve.
(II) Tipping bucket type
Tipping bucket-type rain gauge is a 30 cm sized circular rain gauge adopted for use by the US weather bureau. It has a 30 cm diameter sharp-edged receiver and at the end of the receiver is provided a funnel.
Pair of buckets are pivoted under this funnel in such a manner that when one bucket receives 0.25 mm of precipitation, it tips discharging its rainfall into the container, bringing the other bucket under the funnel.
Tipping of bucket completes an electric circuit causing the movement of the pen to mark on a clock-driven receiving drum which carries a recorded sheet. These electric pulses generated are recorded at the control room far away from the rain gauge station. This instrument is further suited for digitalizing the output signal.
(III) Floating or natural syphon type rain gauge
The working of this type of rain gauge is similar to weighing bucket rain gauge. A funnel receives the water which is collected in a rectangular container. A float is provided at the bottom of the container, and this float raises as the water level rises in the container. Its movement is recorded by a pen moving on a recording drum actuated by clockwork.
When the water rises, this float reaches the top floating in the water, then the siphon comes into operation and releases the water outwards through the connecting pipe, hence all water inbox is drained out. The curve drawn using this data is known as the mass curve of rainfall.