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Rain Gauge

Siting A Rain Sensor

Simply put, rain gauges are used to record the cumulative precipitation at a given location for a given time. There are a variety of factors that can affect rain gauge measurements. Buildings, landscaping and trees, and even the wind can impact the amount of precipitation reaching the rain detector. Proper placement is critical to ensure that rain sensor readings are an accurate representation of the actual rain measurement rates and amounts that have fallen.

The ideal site for a rain gauge is in an open area that is protected from the wind in all directions, such as in a large inner court yard, an unlikely possibility for most owners of weather stations. Therefore, rain gauges should be sited in an open area away from the external factors mentioned above. A good guideline to follow as a minimum distance from these objects is twice their height. This may be difficult in some situations, so the best compromise is to stay as far away as possible from the objects and ideally no closer than half their height. Digital and wireless rain gauges are often the best choice for difficult installation locations.

Rain gauges should also be sited relatively close to the ground but not so close that precipitation falling next to the rain detector splashes into it. The minimum guideline is no lower than two feet. However, the issue with height isn't limited to the rain gauge being too close to the ground. The rain sensor can also be sited too high. This was demonstrated over two centuries ago (1769) when a rain gauge was placed atop a 30 foot tall house and it received only 80% of the amount that a ground-based rain gauge measured. Another rain sensor was placed on top of a 150 foot church tower and it only received 50% of the ground level rain detector measurement! It wasn't until the late 1800s that researchers learned why. Wind was the culprit! What then is the best rain gauge height? Actually the minimum guideline of two feet is best and no higher than six feet.

Finally, to ensure optimal performance, rain gauges must be mounted on a vibration-free level surface. Use a bubble level to make sure that the surface is indeed level. This is critical to the accuracy of the most common type of rain detector sensor, the tipping bucket rain gauge, which degrades significantly if installed on a non-level plane.

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