A rain gauge is any device used to measure the amount and rate of liquid precipitation. The standard unit of measurement is the millimetre (mm). The type of instrument used is usually dictated by whether the weather station is manned or automatic.
Collecting Bottle:
In the former the calibrated collection bottle is still widely used. A calibrated bottle can’t be beaten for an accurate measure of rainfall amount, it never needs recalibrating and there is nothing much to go wrong.
An ornate version of a measuring bottle type rain gauge.
The collecting bottle does of course rely on regular checks in order that the rate of rainfall can be calculated and even then it will not be possible to track rainfall rates in real time.
Weighing Gauge:
These collecting bottles sit on a scale and the precipitation is measured by weight, this type can be linked to a recording mechanism (such as a simple chart printout or logged to a computer). When recorded in this manner real time rainfall rates can be recorded. The down side of this type of instrument is the cost and relative complexity making the purchase and maintenance costs much higher than other types.
The Tipping Bucket Rain Gauge:
Easily the most commonly used rainfall monitoring equipment at automated weather stations.
The precipitation fills one of two balanced buckets which (when a fixed and known amount of precipitation has filled the bucket), tips over and empties the water out of the base of the sensor, the action of tipping over then presents the second bucket to take over.
Inside a Tipping Bucket Rain Gauge
The twin bucket arrangement can be seen in the foreground balanced on top of the “A” frame. When the bucket on the right has side has filled, it will drop down lifting the left hand bucket to the upwards position ready to take over. The cover that sits over the arrangement is in the background.
The capacity of the bucket is known and so a known amount of rain will cause the buckets to tip. Every tip opens and closes an electrical switch. External equipment (the weather station for your home, if you have one for example) will then count the number of switch operations and from that calculate the amount of rain, it will also keep track of the period over which the rain fell and so can report rainfall rates over the last hour or 12 hours or 24 hours etc.
This is the type of rain gauge used at almost every official weather monitoring site around the world. It is simple and reliable. The maintenance largely involves keeping it clear of debris. Calibration testing involves dripping a known quantity of water over a known period of time.
There have been question marks raised about their performance in torrential rain, it is suspected that they may under-read in extremely heavy rain because of the finite time taken to swap between buckets during a tip.
Choosing a good Location for Your Rain Gauge:
Regardless of the type of rain gauge that you choose the siting requirements are the same. The gauge is designed to measure precipitation from the skies only, so keep it well way from any structures which may allow water run-off (or wind-blown water run-off) to reach the measurement mouth.
Ideally they should be located away from solid surfaces (over grass is ideal) to prevent extremely heavy rain bouncing off the ground nearby and entering the gauge.
If you live in an area that will be subjected regularly to sub-zero temperatures then you may wish to consider a heated rain gauge. This prevents the gauge from becoming blocked with snow or ice.
How Do Your Results for Home Weather Station Rainfall Measurement Compare With the Experts?
One of the most enjoyable aspects of owning your own weather station is in comparing results with the big boys. The U.K. Meteorological Office has an excellent display of rainfall data from their rainfall radars why not see how the readings from your rain gauge shape up?
