Rain Gauges – What They Are, How They Work, And The Different Types
Rain Gauges – What They Are, How They Work, And The Different Types
Rainfall measurement is a practice that communities have been following for centuries throughout the world. The device used for measuring precipitation is more commonly known as a rain gauge.
To be more precise, evidence shows the practice of measuring rainfall dates back as far as 500 B.C., when the Ancient Greeks already measured precipitation.
Combined with the record high temperatures recorded in recent years and the resulting shifts in global precipitation patterns, the accurate measurement of rainfall has become more critical than ever before.
This article will focus on what a rain gauge is, highlight the different types of rain gauges, and explain how they work.
What Is A Rain Gauge?
With the importance of measuring and recording rainfall established, we first need to define what a rain gauge is before examining the different types of devices and how they work.
Rain Gauge Definition
A rain gauge is a meteorological instrument used to measure the amount of liquid precipitation in a specific area over a set period of time. It typically forms part of a weather station, where the collected data is used for monitoring and forecasting weather conditions.
Also known as udometers and pluviometers, rain gauges are considered to be one of the oldest meteorological instruments ever invented and are widely used.
To understand how a rain gauge works, one needs to look at the different types of devices for measuring rainfall and examine the unique way in which each one works.
The Different Types Of Rain Gauges
If you look at different rain gauges closely, you will notice that the majority of them work on the same basic principle. The rain falls into a cylindrical funnel that collects the water, which runs down into different measuring mechanisms.
These different mechanisms and methods of collecting and measuring the rainfall make each rain gauge different. There are mainly 5 types of rain gauges:
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- Graduated Cylinder Rain Gauge (Standard Rain Gauge)
- Tipping Bucket Rain Gauge
- Weighing Precipitation Gauge
- Optical Rain Gauge
- Acoustic Rain Gauge
Each rain gauge serves a different purpose, depending on the needs of the meteorologist, hydrologist, or home weather enthusiast.
1. Graduated Cylinder Rain Gauge
Also known as the standard rain gauge, the graduated cylinder rain gauge is a simple glass cylinder with measurement markings. It is used by professional weather services in manned stations and is one of the most accurate ways of directly measuring rainfall.
The water is collected by a cylindrical funnel, from where it flows directly into the graduated cylinder, or it is captured in a container and then poured into a measuring cylinder.
This rain gauge must be measured and emptied on a daily basis, which means it can only be used in a manned weather station. (Remote weather stations use automated rain gauges that empty themselves, which you will learn about shortly.)
The United States (NWS) and the United Kingdom (Met Office) use two different methods for measuring rainfall in a graduated cylinder rain gauge:
National Weather Service 8 Inch Standard Rain Gauge (United States)
The United States National Weather Service uses the 8-inch Standard Rain Gauge. It consists of four main components:
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- Collector Funnel
- Measuring Tube
- Overflow Can
- Measuring Stick
The collector funnel catches the rain and is 8 inches in diameter. From there, the water flows directly into the measuring tube. The tube is either a plastic or brass tube.
The measuring tube is housed in the overflow can, which catches all the water that overflows from the measuring tube. It can hold a maximum of 20 inches of liquid.
The fourth component of the rain gauge is the graduated measuring stick with distinct white markings. A meteorologist measures rainfall by dipping it through the funnel opening to the bottom of the measuring tube and records the reading.
If the rainfall exceeds the maximum 2 inches the measuring tube can contain, it flows into the overflow can. The contents are then poured into a graduated measuring tube and measured separately.
Met Office 5 Inch Standard Rain Gauge (United Kingdom)
The United Kingdom’s Met Office uses the 5-inch Standard Rain Gauge. It also consists of three main components:
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- Collector Funnel
- Glass Container
- Graduated Measuring Tube
The funnel catches the rain and is 5 inches in diameter. From there, the water flows directly into a large, plain glass container.
Once a day, the glass container is removed, and its contents are poured into the graduated measuring tube, which measures the amount of rainfall.
2. Tipping Bucket Rain Gauge
The tipping bucket rain gauge is an automated rain meter that uses a “tipping bucket” mechanism to measure rainfall. It is used by professional weather services’ remote weather stations and is also popular and widely used in home weather stations.
Like a standard rain gauge, it uses a collector funnel with a narrow pipe at the bottom to capture rainfall. From the pipe, the water drops onto a finely-balanced seesaw device with small buckets on each side.
At any point, one of the buckets is positioned directly under the pipe. When enough water collects in the bucket, its weight causes it to tip downward, emptying itself while lifting the opposite bucket into position under the pipe.
This process keeps repeating as rainwater continues to flow through the funnel onto the buckets. Each time a bucket tips, it triggers an electronic switch. In turn, the switch sends a wireless or landline signal to a base station.
Each signal represents a specific amount of rain that has been set up and calibrated in the tipping bucket mechanism. By counting each signal and adding it up, weather stations can calculate the rainfall over any given period.
As the water flows out of each bucket, it drains through predesigned openings in the rain gauge, meaning it does not need to be manually emptied. This advantage makes it ideal for use in remote weather stations, which are often hard to reach.
3. Weighing Precipitation Gauge
A weighing precipitation gauge consists of a receiving bucket mounted on a weighing device, usually a mechanical mechanism such as a spring. The rain accumulates in the container, and the increased weight compresses the springs.
The amount of compression is measured and used to calculate the weight of the water. The measurement can be recorded manually with a pen on a drum or electronically with a data logger and sent to the base weather station via landline or wireless connection.
The weighing precipitation gauge has some advantages over the tipping bucket system, including the ability to capture and measure snow and other solid forms of precipitation. It is also better equipped to handle large downpours.
Most modern systems are also self-emptying, reducing the amount of maintenance required on this type of rain gauge. Some weighing gauges are heated as well, which allows them to melt solid forms of precipitation and prevent a build-up of snow.
4. Optical Rain Gauge
An optical rain gauge consists of a laser or infrared diode and a photosensitive sensor positioned in enclosed compartments on opposite sides beneath a row of funnels that receive rainfall.
Each funnel has a small opening at the bottom through which a raindrop forms when enough precipitation accumulates inside the container. Once the water drop 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 enough for the photosensor to detect and measure it. These measurements are recorded and sent through a landline or wireless connection to the base weather station.
Optical rain sensors have the advantage of not only measuring the amount of rainfall, but also its intensity and frequency through precise detection by the photosensitive sensor.
5. Acoustic Rain Gauge
Acoustic rain gauges use hydrophones and are typically deployed to measure rainfall over large bodies of water like dams, lakes, and the ocean.
The device itself is placed beneath the water’s surface. The hydrophone senses and measures the impact of raindrops hitting the surface.
Each raindrop makes a unique sound, depending on its size and speed, which is called a sound signature. An acoustic rain gauge is sensitive enough to detect the different sound signatures to calculate the size and frequency of different raindrops.
Identifying The different Types Of Rain Gauges
Even though many rain gauges operate on similar principles, they can be identified by a few key visual characteristics:
Graduated Cylinder (Standard Gauge): Identified as a clear outer cylinder with a visible inner measuring tube.
Tipping Bucket Gauge: Identified as an enclosed housing, which usually forms part of an automated weather station with electronic components.
Weighing Precipitation Gauge: Identified as a larger enclosed unit, often heated, with no visible internal measuring scale.
Optical Rain Gauge: Identified as small funnels positioned above a sensor housing with no collecting bucket.
Acoustic Rain Gauge: Identified as a submerged device placed beneath the surface of water, which is not visible above ground.
Conclusion
After reading this post, you will know just how vital rainfall is to scientists, especially meteorologists and hydrologists. This is the reason why so much focus and time is spent on measuring precipitation, and it also explains why so many different rain gauges are in use.
This article focused on what precisely a rain gauge is and also examined the different types of rain measuring devices and how they work in different environments to make accurate precipitation measurements.
Until next time, keep your eye on the weather!