Rain Gauges: What They Are, How They Work, And The Different Types Of Rain Gauges
Rainfall measurement is an age-old practice that communities have been engaging in for centuries throughout the world. The device used for measuring precipitation is more commonly known as a rain gauge.
A rain gauge can predominantly be defined as a meteorological instrument used to measure the amount of precipitation in its liquid form in a specific area over a defined period of time. It typically forms part of a weather station to measure current and determine future weather conditions.
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, which lead to a global reduction in precipitation, the accurate measuring 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.
Rain Gauge Definition
With any doubt about the importance of measuring and keeping a record of rainfall out of the way, we first need to define what precisely a rain gauge is before looking at different types of devices and how they work.
What Is A Rain Gauge?
A rain gauge is a meteorological instrument used to measure precipitation in its liquid form in a specific area over a predetermined period of time. It is typically used as part of a weather station to measure current and determine future weather conditions, monitoring the water cycle, as well as refining forecasting models.
Also known as udometers and pluviometers, rain gauges are considered to be one of the oldest meteorological instruments ever invented and 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:
- 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, measured glass cylinder. It is used by all professional weather services in manned stations and is the most accurate way of directly measuring rainfall.
The water gets collected by a cylindrical funnel, from where it flows directly into the graduated cylinder or captured by a container and then poured into a measured cylinder.
This rain gauge has to 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 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:
- 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 record the reading.
If the rainfall exceeds the maximum 2 inches the measuring tube can contain, it flows into the overflow can which, contents get measured separately by pouring it into a graduated measuring tube which records the reading.
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:
- 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 plain large glass container.
Once a day, the glass container is removed, and its contents 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 makes it drops to the bottom and empties 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 drops to the bottom, 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 there is no need for anyone to maintain the system. This advantage makes it ideal for use in remote weather stations, which is also hard to reach.
3. Weighing Precipitation Gauge
A weighing precipitation gauge consists of 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 gets 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 send 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/infrared diode and photosensitive sensor situated in enclosed spaces on opposites 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. Once 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 send 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 the intensity and frequency of the rain through precise detection by the photosensitive detector.
5. Acoustic Rain Gauge
Also known as hydrophones, acoustic rain gauges are used to measure the rainfall over large bodies of water like dams, lakes, and the ocean.
The device itself gets place underneath the water's surface. 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. An acoustic rain gauge is sensitive enough to detect the different sound signatures to calculate the size and frequency of different raindrops.
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.
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Until next time, keep your eye on the weather!