Know More About Rain Gauge Types And Their Uses

Types of rain gauges

Rain gauge is a  hydrological instrument used for measuring rainfall there are two types of rain gauges.

1. Non-Recording Or Ordinary Rain Gauges.
2. Recording Type Or Automatic Rain Gauges.

Non-recording or ordinary rain gauges:

It consists of a funnel of diameter 125mm and the end of the funnel goes into a collecting bottle (or a precise measuring cylinder with 0.1mm graduations )  both the funnel and collecting bottle are housed in a metal enclosure or in an FRP housing.

The latest construction as per IMD norms are that the funnel and the outer body is integrated as one piece and a gunmetal rim is inserted in the top of the funnel, the lower portion of the FRP body is locked into the upper body(which houses the funnel) with an aluminium locking ring,  a plastic collector is placed inside the lower body which collects the rainfall. 

The user then visits the site daily, and pours the collected rainfall into the measuring cylinder, and reads out the volume of rain per day which represents the rainfall per duration of time. 

Recording / Digital Logging Rain Gauges:

The recording gauge records rainfall against time. Therefore, the duration and intensity of rainfall can easily be viewed and stored for further studies and rainfall prediction,  provided at least 10 years of data is analysed.

Recording Rain Gauges Can Be Subdivided As Under

1. Tipping Bucket Type:

•  It consists of a 20.4 cm diameter sharp edge self-emptying collector as per WMO guidelines.
• A pair of buckets 0.254mm capacity are pivoted on the collector in such a way that when one bucket receives 0.254 mm of rainfall it tips, discharging its contents and bringing the other bucket under the funnel.
• One tip of the bucket activates an electronic reed switch and one pulse is sent to the logger which represents 0.25mm of rainfall some units send one pulse after 2 tips. This is logged in a button-type logger which also displays the rainfall with respect to time. 
• Data is then downloaded to a computer and stored for further analysis.
• Thus, this type of gauge gives rainfall vs time and duration plus intensity for a particular period of a particular place can be determined.
• This type is not suitable for very high rainfall in a short duration of time.

2. Recording Rain gauge Syphon (Float) type:

As per IMD norms, this Rain gauge is made from FRP in 2 parts just like the nonrecording rain gauge. The funnel has a diameter 203.4mm or 125mm for normal and heavy rainfall respectively.

Rainfall collected by the funnel trickles into a brass chamber containing a brass float (float chamber) of a particular weight the increasing rain causes the float to rise. The chamber is machined precisely to accommodate 10mm of rainfall to an accuracy of 0.2mm. 

When the float rises, a pen filled with recording ink,  which is attached to the float, through a lever system records the elevation of the float, on a rotating drum driven by a clock mechanism on which is wound a daily or a weekly graph paper, since the pen is just touching the graph paper, it traces a graph with respect to time thus the duration and intensity of rainfall is recorded.

The user changes the graph paper daily or weekly as per his desire. When the float has reached a maximum of 10mm the siphon arrangement empties the float chamber. And the float needs to come to 0 from a max of 10mm within a time of 15 seconds the rain gauge is then ready to start recording again.

Information about the beginning and end of the rain, its intensity, duration,  can easily be obtained from the graph, which is then filed for further studies.

3. Weighing Bucket-Type Rain Gauges:

This type of rain gauge is similar to the syphon type only the syphon and float mechanism is replaced by a spring balance type mechanism, so the pen which is connected to the spring balance moves as the chamber is filled with rain, can be used for recording rainfall as well as snowfall. This rain gauge is not yet used in India. 

4. Ultrasonic Rain Gauge/ Optical Rain Gauge:

This is similar to the tipping bucket only the bucket and reed switch is replaced with ultrasonic sensors and each drop scatters the sound waves to give a reading in mm of rainfall Ultrasonic rain gauge is a  high-precision rain gauge based on the principle of ultrasonic ranging, accuracy can reach 0.1mm.

It is ideal equipment for a meteorological and hydrological measurement system The product is composed of a rainwater collector,  a measuring subsystem, and a cleaning subsystem.

Ultrasonic rain gauge measurement time is short, one measurement can be completed in 2 seconds, the measurement frequency can reach once per minute, The whole rain gauge has no mechanical transmission parts, which increases the service life of the rain gauge.

Similarly, an optical rain gauge consists of a laser/infrared diode and photosensitive sensor situated in enclosed spaces on opposite sides and below a row of funnels that receive rainfall.

Each funnel has a small opening at the bottom through which raindrop forms when enough precipitation accumulates inside the container and when the waterdrop grows large enough, it falls from the funnel and through the space between the laser diode and photosensor.

As the drop falls through the beam of light, it scatters it enough for the photosensor to detect and measure it. These measurements are recorded and stored for further analysis.

Optical rain sensors have the advantage of not only measuring the amount of rainfall but also the intensity and frequency of the rain through precise detection by the photosensitive detector.

5. Hydrophones:

Acoustic rain gauges are used to measure the rainfall over large bodies of water like dams, lakes, and the ocean. The device itself is placed underwater. The hydrophone can sense and measure the impact of the raindrops hitting the surface of the water.

Each raindrop makes a unique sound, depending on its size and speed, which is called a sound signature the rain gauge detects the different sound signatures to calculate the size and frequency of different raindrops.

This is a highly advanced unit and is used basically in river surveys in dams’ rivers etc.

LYNX – Lawrence & Mayo are the leading rain gauge manufacturers in India. To request a quote, contact us on 9483511877 or visit our website.