Precipitation observation instruments

Precipitation observation instruments are indispensable tools in meteorology and hydrology for accurate measurement of rainfall. According to the working principle and structural composition, the common precipitation observation instruments mainly include the following types:

 1. Tipping bucket rain gauge

Working principle of tipping bucket rain gauge  

A tipping bucket rain gauge collects rainwater through a tilting funnel. When a preset amount (e.g. 0.2 or 0.5 mm) is accumulated, the bucket will turn over and dump the water, triggering a sensor to record a rainfall event. Each flip of the bucket represents a specific amount of precipitation, and the cumulative number of flips is the total amount of precipitation.

Advantages of tipping bucket rain gauge

- Highly accurate: it can record precipitation in real time and accurately, and is not affected by external factors such as dust and shadows.

- Protective: rugged design, suitable for long-term outdoor use, especially in bad weather conditions, stable performance.

- Simple maintenance: simple structure, easy to clean and replace parts, reducing the cost of use and maintenance difficulty.

Disadvantages of tipping bucket rain gauges

- Large size: Compared with other types of rain gauges, tipping bucket rain gauge is larger in size and requires more space for installation.

Application Scenarios of Tipping Bucket Type Rain Gauge

- Meteorological stations, agricultural irrigation, hydrological monitoring, flood prevention and early warning.

 2. Optical rain gauge

Optical rain gauge working principle  

Optical rain gauge utilizes optical principle to measure rainfall. The sensor contains a light source and a receiver, and determines the amount of rainfall by measuring the attenuation of light. When a raindrop falls on the sensor, it blocks some of the light, resulting in a change in light intensity, and the system calculates the amount of precipitation based on this change.

Optical Rain Gauge Advantages

- Compact size: easy to install for applications where space is limited.

- No mechanical movement required: reduces the possibility of mechanical wear and tear and malfunction.

Optical Rain Gauge Disadvantages

- Susceptible to environmental interference: accumulated dust, leaves swinging and other external factors will affect the optical path, resulting in measurement errors.

- Poor accuracy: limited ability to detect tiny raindrops (e.g. drizzle) and prone to false alarms.

Optical Rain Gauge Application Scenarios

- Precipitation monitoring in indoor or controlled environments, e.g. laboratories, greenhouses, etc.

 3. Piezoelectric Rain Gauge

Piezoelectric rain gauge working principle  

Piezoelectric rain gauges utilize the piezoelectric effect to measure rainfall. When a raindrop falls on the surface of the sensor, a pressure change occurs and the piezoelectric material produces a charge output, which is measured to determine the amount of precipitation.

Advantages of Piezoelectric Rain Gauges

- Fast response: Capable of capturing raindrops quickly, suitable for high precision and fast response application scenarios.

- Highly resistant to interference: less susceptible to external factors such as wind and snow, and more adaptable.

Disadvantages of piezoelectric rain gauge

- Difficult to monitor small rain intensity: limited ability to detect tiny raindrops (e.g., hairy rain, sunshine rain).

- Easily misjudged: In sandy weather, wind and sand hitting the sensor surface will produce pressure changes similar to raindrops, leading to misjudgment as rainfall.

- Limited accuracy: Measurement data is affected by factors such as raindrop size, shape, and speed, reducing the accuracy of the measurement.

Application Scenarios

- High-precision meteorological monitoring, scientific research fields, urban drainage system monitoring, etc.

 Why does the piezoelectric rain gauge misinterpret sand and dust as rainfall?

The working principle of the piezoelectric rain gauge is based on the piezoelectric effect of piezoelectric ceramics. When wind sand and other debris in dusty weather hits the surface of the sensor, it will produce a pressure change similar to that of a raindrop collision, and the sensor will misjudge it as a raindrop impact, and thus misjudge that there is rain. This kind of misjudgment is especially common in long-term monitoring in the field, especially in areas with high wind and sand.

 Advantages and selection guide for tipping bucket rain gauges

Despite its large size, the tipping bucket rain gauge has unrivaled advantages in other areas, especially in terms of accuracy and reliability. It measures efficiently, is sensitive, protective and, most importantly, accurate! It records precipitation in real time and accurately, unaffected by dust and shadows. Combined with the well-designed tipping bucket structure and precise counting system, it maintains high-precision measurements even under adverse weather conditions. The tipping bucket rain gauge calculates the rainfall per square meter by dividing the rainfall measured per minute by the cross-sectional area of the rain bearing opening, so the rain bearing aperture is the key parameter for calculating the rainfall per square meter. The following are key considerations when selecting a tipping bucket rain gauge:

 1. Design of the Rain Gauge

One of the most important factors affecting the measurement accuracy of tipping bucket rain gauges is the rainfall bearing port. According to the national standard GB/T 21978.2-2014, the design of the rain bearing opening should meet the following requirements:

- Size of the inner diameter of the rain-bearing opening: 200mm. this size can effectively collect different types of precipitation (light rain, medium rain, heavy rain, heavy rain, etc.), and also avoid rain splashing or overflowing due to the small caliber, ensuring the accuracy of the measurement results.

- Blade angle: 40°~45°. When the angle of the cutting edge is within this range, it can accurately divide the rainwater it receives, clearly defining where the raindrops fall and avoiding the creation of fuzzy areas. The cutting edge also helps to minimize the interference of external factors (e.g. wind, foreign objects) on rainwater collection.

 Ps: When rainwater falls and touches the edge, it will flow into the hopper evenly and in an orderly manner according to the shape and design of the edge, avoiding uncontrolled splashing or diffusion of rainwater at the mouth of the hopper, ensuring that each hopper receives the same amount of rainwater, providing the basis for accurate measurement of rainfall. Without an edge, rainwater may flow randomly into the hopper, resulting in large differences in the amount of rainwater collected by each hopper. At the same time, the cutting edge also helps to minimize the interference of external factors (e.g. wind, foreign objects, etc.) on rainwater collection, and also prevents larger foreign objects from directly entering the tipping bucket, which may affect the normal tipping of the bucket and the accuracy of measurement. 

- Material and depth of the inner wall: the rainwater bearing mouth should be made of materials that are not easily deformed, with a smooth inner wall and a depth of not less than 100mm, in order to prevent the rainwater from splashing out of the rainwater bearing mouth due to the impact force, which will affect the accuracy of the measurement.

 2. Ensure the accuracy

According to the national standard, the accuracy of tipping bucket rain gauge is divided into three levels, as follows:

Selection should be based on the actual needs to choose the appropriate accuracy level, especially for meteorological scientific research and other fields, it is recommended to choose the higher accuracy of class I equipment.

 3. Selection of resolving power of tipping bucket rain gauge

The resolution of tipping bucket rain gauge is divided into four specifications: 0.1mm, 0.2mm, 0.5mm, 1.0mm, different resolution for different application scenarios:

- 0.1mm: Suitable for meteorological scientific research, capable of capturing extremely subtle changes in rainfall, which helps in the in-depth study of the evolution of weather systems and the improvement of climate models.

- 0.2mm/0.5mm: Suitable for daily application scenarios, such as urban flood control monitoring, agricultural irrigation guidance, etc., capable of meeting the demand for approximate magnitude and trend of rainfall.

- 1.0mm: applicable to scenes with lower requirements for accuracy, such as hydrological monitoring of large areas.

 4. Rainfall intensity measurement range

The tipping bucket rain gauge should maintain high measurement accuracy within the rainfall intensity range of 0.01 mm/min to 4.0 mm/min. Beyond this range, problems such as the tipping bucket turning too fast or too slow, rain splashing, residual water, etc., may occur, affecting the accuracy of the measurement.

Piezoelectric rain gauges maintain high measurement accuracy within the rainfall intensity range of 0.01 mm/min to 8.0 mm/min. Therefore, when selecting one, it is important to confirm that the device is capable of functioning properly within this range and to specify the maximum rainfall intensity allowed to pass.

 5. Design of internal structure of tipping bucket rain gauge

- Single tipping bucket rain gauge: simple design, consisting of a funnel and a tipping bucket, suitable for general application scenarios, easy to install and maintain.

- Double tipping bucket rain gauge: adopts two tipping buckets, the upper one is a transition tipping bucket, and the lower one is a measuring tipping bucket, which can continuously and evenly inject natural precipitation with different strengths into the measuring tipping bucket, and improve the accuracy of precipitation detection. It is suitable for occasions that require high precision measurement.

 6. Working environment conditions of tipping bucket rain gauge

The tipping bucket rain gauge should work normally under the following environmental conditions:

- Temperature: 0℃~55℃.

- Relative humidity: not more than 95% (40℃ condensation)

High temperature, low temperature and high humidity environments may affect the performance of the mechanical parts and electronic components of the rain gauge, resulting in decreased accuracy or malfunction. Therefore, selection should be made to ensure that the device can operate stably in the expected operating environment.

 Conclusion

The selection of precipitation observation instruments should be based on comprehensive consideration of specific application scenarios and needs. With its high accuracy, reliability and wide applicability, the tipping bucket rain gauge has become the first choice for precipitation observation, especially in the fields of meteorology, hydrology and agriculture. The selection should focus on the design of the rain-bearing port, accuracy level, resolving power, rainfall intensity measurement range, internal structure design and working environment conditions to ensure that the equipment can meet the actual needs and provide reliable measurement data.

Tipping bucket rain gauge data sheet

NBL-W-ARS-Tipping-bucket-rain-gauge-instruction-manual.pdf

NBL-W-RS-Rain-sensors-instruction-manual-V4.0.pdf

NBL-W-DRS-Double-Tipping-Bucket-Rain-Sensor-Instruction-Manual.pdf

Piezoelectric Rain Gauge data sheet

NBL-W-PRS-Piezoelectric-Rain-Sensor-Operator's-Manual.pdf