Rain Gauges Definitive Guide For 2022

Precipitation Gauge | Rain Sensor | Pluviometer

How to Measure Rainfall?

Rain Gauges!

A rain gauge (also known as an udometer, pluviometer, or an ombrometer) is an instrument to gather and measure the amount of liquid precipitation over a set period of time.

It is also an important part of automatic weather station.

Before introducing the rain gauge, I would like to introduce the definition of precipitation.

Let’s Go!

Definitions of Precipitation

Chapter 1

What is precipitation?

Precipitation is defined as the liquid or solid products of the condensation of water vapour falling from clouds or deposited from air onto the ground.

Types of precipitation includes rain, hail, snow, dew, rime, hoar frost and fog precipitation.

Snowfall is also expressed by the depth of fresh, newly fallen snow covering an even horizontal surface .

Precipitation intensity is defined as the amount of precipitation collected per unit time interval.

According to this definition, precipitation intensity data can be derived from the measurement of precipitation amount using an ordinary precipitation gauge.

Note

Units and scales

The unit of precipitation is linear depth, usually in millimetres (volume/area), or kg m–2 (mass/area) for liquid precipitation.

Daily amounts of precipitation should be read to the nearest 0.2 mm and, if feasible, to the nearest 0.1 mm; weekly or monthly amounts should be read to the nearest 1 mm (at least).

Daily measurements of precipitation should be taken at fixed times common to the entire network or networks of interest.

The measurement unit of rainfall intensity is linear depth per hour, usually in millimetres per hour (mm h–1).

Rainfall intensity is normally measured or derived over one-minute time intervals due to the high variability of intensity from minute to minute.

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Rain Gauges Definition & Principle

Chapter 2

What Is Tipping Bucket Rain Gauge

ZATA ZDR100 Tipping Bucket Rain Gauge

The tipping-bucket raingauge is used for measuring accumulated totals, the rate of rainfall and intensity precipitation.

As recommended by WMO, it is a professional rain gauge.

Tipping-bucket rain gauge can be divided into single tipping and double tipping. Double tipping rain gauge has higher precision, up to 0.1mm.

This kind of rain gauge is very suitable for meteorology, hydrology, agriculture, forest and etc, in which liquid water precipitation be measured, which is also the main part of professional weather stations.

The output is two wires cable of which gives on and off signals(dry reed).

Tipping Rain Gauge Principle

The principle behind the operation of this instrument is simple.

How does a rain gauge work?

A tipping-bucket raingauge uses a metallic or plastic twin bucket balance to measure the incoming water in portions of equal weight.

When one bucket is full, its centre of mass is outside the pivot and the balance tips, dumping the collected water and bringing the other bucket into position to collect.

The bucket compartments are shaped in such a way that the water is emptied from the lower one. The water mass content of the bucket is constant (m [g]).

Therefore, by using the density of water (r = 1 g/cm3), the corresponding volume (V [cm3]) is derived from the weight of the water and, consequently, the corresponding accumulation height (h [mm]) is retrieved by using the area of the collector (S [cm2]). The equation is:

V=m/ρ=h×S

Thus, by using the density of water, h is calculated, where 1 mm corresponds to 1 g of water over an area of 10 cm2 .

To have detailed records of precipitation, the amount of rain should not exceed 0.2 mm. For a gauge area of 1 000 cm2, this corresponds to a bucket content of 20 g of water.

The raw output is a contact closure (reed switch or relay contact), so each tip produces an electrical impulse as a signal output which must be recorded by a data logger.

Note

rain sensor windshields around the gauge reduce the error caused by deformation of the wind field above the gauge.

What Is Weighing Rain Gauge

The weighing rain gauge is an instrument for calculating rainfall accumulated totals based on the weight of precipitation.

All precipitation, both liquid and solid, is recorded as it falls.

This type of gauge normally has no provision for emptying itself.

The capacity (namely, the maximum accumulation between recharge) ranges from 250 to 1 500 mm depending on the model.

Weighing Rain Gauge Principle

Weighing bucket type rain gauge is most common self-recording rain gauge. It consists of a receiver bucket supported by a spring or lever balance or some other weighing mechanism.

The movement of bucket due to its increasing weight is transmitted to a pen which traces record or some marking on a clock driven chart.

Weighing bucket type rain gauge instrument gives a plot of the accumulated (increased) rainfall values against the elapsed time and the curve so formed is called the mass curve.

Therefore, mechanical degradation and the resulting need for maintenance are significantly reduced.

Weighing technology combined with a self-emptying tipping-bucket allows to perform high resolution and high precision measurements at a very small construction volume.

This type of instruments measures the weight of water in a tipping-bucket with a volume of up to 20 ml and can determine smaller amounts of precipitation compared to “classic” tipping-bucket gauges.

What Is Float Rain Gauge

Float Rain Gauge is a pen-mounted recorder, which writes rainfall values by accumulating rainfall volume and then using a floating pen. It is not a electronic rain gauge.

Float Rain Gauge Principle

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 container, and this float raises as the water level rises in the container.

Its movement being recorded by a pen moving on a recording drum actuated by a clock work.

When water rises, this float reaches to the top floating in water, then syphon comes into operation and releases the water outwards through the connecting pipe, thus all water in box is drained out.

Note

A large undercatch by unshielded heated gauges, caused by the wind and the evaporation of melting snow, has been reported in some countries, as is the case for weighing gauges

A heating device (preferably controlled by a thermostat) should be installed inside the gauge if there is a possibility that water might freeze in the float chamber during the winter.

This will prevent damage to the float and float chamber and will enable rain to be recorded during that period.

The amount of heat supplied should be kept to the minimum necessary in order to prevent freezing.

Because of the heat may reduce the accuracy of the observations by stimulating vertical air movements above the gauge and increasing evaporation losses.

Note

Apart from the fact that calibration is performed using a known volume of water, the maintenance procedures for this gauge are similar to those of the weighing-recording gauge

Further Technology Rain Gauge

With the growth of measurement electronics technologies and smart instruments, other precipitation sensors have been developed in recent years.

Their performance is approximately of the same quality as performance of conventional tipping bucket rain gauges.

Those instruments provide rain intensity with higher resolution comparing to classic methods.

Starting from 0.01 mm, and are particularly suitable for areas which are difficult to access due to being less maintenance demainding devices.

What Is Optical Rain Sensor

Optical rain sensors, using forward-scatter technology or transmittance measurement technology, have been used operationally for decades.

In forward-scatter technology, precipitation detection and identification is based on light scattering properties of hydrometeors, while transmittance measurement technology is based on light attenuation of hydrometeors.

The advantage of optical rain sensor is that it can be used for all precipitation types in all weather conditions.

Furthermore, forward-scatter precipitation sensor is usually able to report MOR as well.

What Is Capacitance Rain Sensor

rain sensors are based on measuring the dielectricity of water. They typically consist of surface capacitance measurement.

As alone, they can be used to detect the precipitation onset and end of an event. They can also be used as supportive measurement with other technologies.

What Is Haptic Rain Sensor

Haptic rain sensors are based on measuring the impact from a hydrometeor.

They typically consist of a piezoelectric sensor to detect the acoustic properties of impact. These sensors are practically maintenance-free.

It is important to deal with the interference of external factors in the design of this instrument. Such as foreign matter, birds or other vibration effects.

What Is Rada Rain Sensor

How is precipitation measured by precipitation radar?

Radar rain sensors, using Doppler radar technology, have the advantage to measure the speed of most forms of condensed water, precipitation quantity and precipitation type (rain, snow, sleet, freezing rain, hail) from the first drops with a fast response time.

At the same time, we need to consider the external interference and improve the processing ability of the algorithm, such as dust storm weather, foreign body false alarm, etc.

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Snow & Ice Measurement

Chapter 3

Snowfall is the depth of freshly fallen snow deposited over a specified period (generally 24 h). Thus, snowfall does not include the deposition of drifting or blowing snow.

For the purposes of depth measurements, the term “snow” should also include ice pellets, glaze, hail, and sheet ice formed directly or indirectly from precipitation.

Snow depth usually means the total depth of snow on the ground at the time of observation.

The water equivalent of a snow cover is the vertical depth of the water that would be obtained by melting the snow cover.

What Is Ultrasonic Snow Depth Sensor

Several ultrasonic models exist on the market and are commonly used with automatic systems.

This type of sensor can also be utilized to control the quality of automatic recording gauge measurements by providing additional details on the type, amount and timing of precipitation.

It is capable of an uncertainty of ±1 cm.
The temperature correction formula for ultrasonic snow depth measurement is:

where d is the snow depth in cm; dr is the raw value of snow depth in cm; T is the air temperature in K; and T = 273.15 + t, t is the air temperature in °C.

What Is Laser Snow Depth Sensor

Laser snow depth sensor detects the snow depth distance to the ground by comparing phase information.

The measurement of the distance is independent of air temperature, but may depend on the penetration of the laser beam in the snow surface according to the type of snow.

The laser spot is also very small, increasing the importance of ground surface representativeness. It is strongly recommended using a laser beam classified safe for the eyes (maximum power class 2).

To get reliable snow height data between 0 and 2 cm it must be ensured by the setup that the measured distance is fixed under all conditions.

Note: Due to lifting and lowering of the ground dependent of type of soil, temperature, moisture and frost sometimes more than +/- 1 cm must be considered.

Note

An area with natural vegetation can create issues, so it may be better to use a stable and controlled surface, such as a snow plate.

What Is Ice Sensor

At meteorological stations, the observation of ice accumulation is generally more qualitative than quantitative, primarily due to the lack of a suitable sensor.

Ice accretion indicators, usually made of anodized aluminium, are used to observe and report the occurrence of freezing precipitation, frost or rime icing.

Ice On Pavement

Direct Measurement

One sensor using two electrodes embedded in the road, flush with the surface, measures the electrical conductivity of the surface and readily distinguishes between dry and wet surfaces.

Remote Measurement

ZATA ZRS Road Sensor

There are two remote-sensing methods under development.

The first method is based on the reflection of infrared and microwave radiation at several frequencies (about 3 000 nm and 3 GHz, respectively).

The microwave reflections can determine the thickness of the water layer (and hence the risk of aquaplaning), but not the ice condition.

Two infrared frequencies can be used to distinguish between dry, wet and icy conditions.

It has also been demonstrated that the magnitude of reflected power at wavelengths around 2 000 nm depends on the thickness of the ice layer.

The second method applies pattern recognition techniques to the reflection of laser light from the pavement, to distinguish between dry and wet surfaces, and black ice.

Rain Gauges Compare Table

Chapter 4

Principle	Advantages	Disadvantages
Tipping Rain Gauge	WMO Standard Maximum dosage Low cost Most widely used Calibration is simple	Can’t monitor snow, ice Unable to eliminate evapotranspiration effects
Weighing Rain Gauge	WMO Standard High accuracy Snow & Ice measurement Decreased evapotranspiration effect	Higher cost More complex installation structure
Float Rain Gauge	WMO Standard Automatic Recording Function Installation easy, Portable	Independent, not accessible to automatic observation systems Rather old generation Not a digital rain gauge
Optical Rain Gauge	High sensitivity Large monitoring range Long life No moving parts, no maintenance	No calibration standard Cost higher than normal
Capacitance Rain Gauge	High sensitivity Qualitative but not quantitative Switch output Low cost	No rainfall output
Haptic Rain Gauge	High sensitivity Snow & Ice measure No moving parts, no maintenance Decreased evapotranspiration effect	Data misreporting Poor consistency in monitoring rainfall intensity Light rain is not as accurate as optical detection
Rada Rain Gauge	High sensitivity Snow & Ice measure No moving parts, no maintenance Decreased evapotranspiration effect	Data misreporting Poor consistency in monitoring rainfall intensity Cost highest

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Rain Gauges Application

Chapter 5

Meteorological industry
- Automatic Weather Station
- Airport AWOS
- Urban Waterlogging
Water Conservancy
- Water loss and soil erosion
- Watercourse Monitoring in Small Watershed
Agriculture and forestry
- Crop growth
- Yield analysis
- Farmland irrigation
- Forest fire prevention
Smart City
- Autopilot
- Monitoring of Urban Pipe Gallery

Find More About Rain Gauges

Chapter 6

1. WikiMedia

Rain Gauge
A rain gauge (also known as an udometer, pluviometer, or an ombrometer) is an instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation over a set period of time.
Contents
1History
1.1National coverage and modern gauges
2Types
2.1Standard rain gauge
2.2Pluviometer of intensities
2.3Weighing precipitation gauge
2.4Tipping bucket rain gauge
2.5Optical rain gauge
2.6Acoustic rain gauge

2. Patents

US20130255783A1:Optical rainfall measuring device
Inventor:Etsuji Ishibashi Tomohiro Kawamoto Takeshi Kawamura Showa Miyauchi 宮内　将和川本　智宏川村　武司石橋　悦治
WO2015071545A1:Rada Precipitation sensor
Inventor: Pauli NylanderTaisto Haavasoja
US20170329049A1:Haptic rain sensor
Inventor: Robert John DerrDavid St. John
Current Assignee: Weatherflow Inc

3. Books

Precipitation (Measuring the Weather)	A Treatise on Meteorology

Provides an introduction to the different types of precipitation and explains how precipitation is related to weather.	A Treatise on Meteorology – The barometer, thermometer, hygrometer, rain-gauge, and ozonometer; with rules and regulations to be observed for their correct use is an unchanged, high-quality reprint of the original edition of 1866.
Buy From Amazon	Buy From Amazon
How to Make a Rain Gauge	Remote Sensing of Clouds and Precipitation

	This book presents current applications of remote sensing techniques for clouds and precipitation for the benefit of students, educators, and scientists. It covers ground-based systems such as weather radars and spaceborne instruments on satellites.
Buy From Amazon	Buy From Amazon