Campbell Scientific (Canada) - Applications

Measuring Rainfall in India

Rainfall is reported as height of liquid in millimeters or inches.So if there was 3 cm of rain, we know 3 cm fell in that area. Measuring rain at an automated weather station is often done using a tipping bucket rain gauge. These devices generate one electronic pulse per tip of an internal bucket. Each tip corresponds to a calibrated volume of water which equates to height of rain that has fallen.

The principle of the tipping bucket rain gauge was developed over 100 years ago. However, research has shown that not all tipping bucket rain gauges are the same or generate the same accuracy. Three different models at a weather station often will report different amounts of rain. Why is this? The answer is shown in the specifications of the sensors. Here are three models available on the market:

MODEL	ACCURACY:
TE525M Texas Electronics	1% up to 25mm/hr
52203 RM Young	3% up to 50mm/hr
TB4 Hydrological Services	3% up to 500 mm/hr

The first thing we notice is that accuracy is stated over a range of intensity, the lowest being 25mm/hr and the highest being 500mm/hr. Tipping bucket accuracy specifications should always include the intensity at which it is valid. The reason for this is because as rain falls into the gauge, the higher the rate the more "sample" is lost. High quality gauges such as the TB4 are engineered to prevent loss and therefore accurately measure rainfall at high intensities. Considering the power of monsoon rains in India, if rainfall measurements are an important aspect of your monitoring, it is highly recommended that you choose a suitable sensor for the conditions. It may cost more, but your data will reflect true conditions.