Rain Gauge Summary
How to measure rainfall using a rain gauge
The barometer must be hung on a wall or a post. Find a place outside for the rain gauge where there will be no run-off of rainwater from trees, roofs or signs. There is a minimum distance official rain gauges must be from obstructions such as these. If a nearby tree is five metres tall, the rain gauge must be at least twice the distance (10 metres) away. Your rain gauge can be set up in three ways, but make sure it is safe from theft and damage (such as being trodden on). * To make a freestanding rain gauge, place the cylinder inside the black holder so the spike points up. This gives a flat base. * To fix the rain gauge to an object such as the top of a fence, secure the black holder to the vertical surface before inserting the cylinder. * To put the gauge at ground level, reverse the black holder so the spike points down (main picture) and stick it into the ground. * At am each day, record the rainfall, referring to the scale (in millimetres) on the cylinder. Then empty the cylinder. If you catch hail or snow, wait for it to melt before taking a reading.
Do's and Don'ts
| Make sure the rain gauge is in a safe location.
| Make sure you take readings with the rainwater at eye level to avoid errors of parallax.
| How does it Work?A rain gauge measures rainfall (in millimetres) over a set period, usually 24 hours. Official rain gauges have a housing to protect the measuring cylinder inside. The top of the housing has a larger surface area than the top of the measuring cylinder and catches more rain than the cylinder would. The extra rainwater collected makes it easier to read the measuring cylinder and improves accuracy. A simple mathematical formula is used to correct the rainfall total to allow for the extra rainwater collected.Formula for Depth of rainfall(inches)= 0.50 x Volume of Rainwater(mm)÷(Diameter of Opening [cm])2
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