Technical Article for Google Search & Professional Meteorological Applications

In meteorology, rainfall refers to the depth of water that falls onto a horizontal surface during a given period under conditions where there is no leakage, evaporation, or runoff. The unit is millimeters per hour (mm/h).

According to the ground meteorological observation guidelines used by meteorological authorities, when precipitation occurs, weather stations need to measure rainfall once every six hours. Based on rainfall amount and rainfall intensity, precipitation can be classified as light rain, moderate rain, heavy rain, rainstorm, severe rainstorm, or extraordinary rainstorm.

Rainfall measurement and statistical analysis are essential parts of meteorological observation. Obtaining rainfall data accurately and in a timely manner is particularly important for preventing and mitigating natural hazards such as floods and droughts, as well as secondary geological hazards such as debris flows, rockfalls, and landslides. Rainfall data are closely connected with production, infrastructure development, and everyday life, and play a significant role in meteorological observation, hydrological measurement, water conservancy development, hydropower engineering, transportation, environmental monitoring, agricultural irrigation, soil and water conservation, flood prevention and emergency command, microwave communications, and engineering management.

Among the small rain gauges commonly used on the market, the main measurement technologies include tipping-bucket, piezoelectric, miniature radar, and optical rain gauges. Their operating principles, advantages, and limitations are summarized below.

1. Tipping-Bucket Rain Gauge

1.1 Measurement Principle

The operating principle of a tipping-bucket rain gauge is relatively simple. As shown in the figure, rainwater first flows through a collection funnel into a small tipping bucket. When the water collected in the bucket reaches a predetermined level, the bucket tips over and discharges the water. Each tipping action triggers a switch, closes the circuit, and sends a pulse signal to the recording device. The data logger records each pulse, and the repeated process is used to measure and record the rainfall event.

Figure 1. Tipping-bucket rain gauge principle diagram. Source image: 

After decades of development, tipping-bucket rain gauges have benefited from mature engineering practices and a well-established measurement principle. Wireless split-type rain gauges are also available today, with the rainfall measurement unit installed outdoors and the display/output unit installed indoors, allowing personnel to observe rainfall data from inside the facility.

1.2 Advantages and Disadvantages

Advantages: The tipping-bucket rain gauge uses a single- or double-bucket configuration and typically provides switching or digital output signals. Compared with other traditional weighing-type rain gauges, it offers a relatively high degree of automation, good timeliness of measurement, low cost, and broad application.

Disadvantages: The capacity of a tipping bucket is limited. Under high rainfall intensity, measurement error increases, making tipping-bucket rain gauges less suitable for high-precision measurement of extreme rainfall. In addition, the relatively complex mechanical structure is exposed to precipitation for long periods and may suffer from corrosion, aging, and sediment accumulation. These conditions increase mechanical resistance and can affect measurement accuracy. Installation also requires a high degree of leveling accuracy. Improper installation can increase measurement errors and shorten the service life of internal moving components.

A tipping-bucket rain gauge mainly measures cumulative rainfall and rainfall intensity at a macroscopic level and has a certain response delay. It is not well suited to monitoring the microscopic characteristics of rainfall, such as raindrop size, velocity, and particle count. Because the water inlet funnel is relatively narrow, clogging can occur easily. In winter, icing must also be prevented, often requiring heating. Frequent manual inspection, maintenance, and servicing may therefore be necessary to ensure normal operation.

2. Piezoelectric Rain Gauge

Figure 2. Piezoelectric rain gauge. Source image:

2.1 Measurement Principle

A rainfall measurement method based on dynamic measurement determines raindrop size indirectly by measuring the impact force generated when raindrops of different sizes strike the sensing surface.

As illustrated in Figure 1(a), a piezoelectric sensing element can be used to estimate raindrop diameter indirectly by measuring the momentum of falling raindrops. The rain sensor consists of a metal housing and a piezoelectric sensing element attached inside the housing. When a raindrop strikes the metal housing, it causes a small mechanical vibration. Under mechanical stress, the piezoelectric element generates a voltage difference between its electrodes and outputs an electrical signal. The greater the impact force, the greater the vibration amplitude and the amplitude of the output voltage. By collecting the piezoelectric output signal, the impact force and falling momentum of the raindrop can therefore be estimated. When the raindrop velocity is known, its diameter can be calculated.

Figure 3. Piezoelectric measurement principle. Source image: 

2.2 Advantages and Disadvantages

Advantages: The equipment is simple and easy to integrate, with relatively high measurement accuracy. It can measure not only macroscopic cumulative rainfall and rainfall intensity, but also microscopic rainfall processes, including raindrop size and falling velocity. Piezoelectric rainfall measurement instruments offer low power consumption, low cost, small size and weight, good real-time response, and a high degree of automation, giving them broad application potential.

Disadvantages: It is difficult to maintain high measurement accuracy simultaneously for heavy rain, light rain, and detailed microscopic rainfall characteristics. Limited sensor sensitivity can make it difficult to accurately measure very small raindrops. Under high rainfall intensity, signals from two raindrops arriving within a short interval can overlap, introducing measurement errors. The system can also be susceptible to external factors such as strong wind, vibration, and lightning, potentially causing misjudgments and measurement errors.

3. Miniature Radar Rain Gauge

Figure 4. Miniature radar rain gauge. Source image:

3.1 Detection Principle

The primary targets detected by miniature radar are raindrops, with diameters ranging from several tens of micrometers to several millimeters. When raindrops interact with the high-frequency electromagnetic waves transmitted by the miniature radar, they scatter the waves and produce reflected signals. By sampling and processing these reflected signals, information such as radial velocity, echo intensity, and radial distribution can be obtained, enabling precipitation detection and quantitative analysis.

The miniature radar typically uses FMCW (Frequency-Modulated Continuous-Wave) technology. A continuous wave with a linearly increasing frequency is transmitted into the air. When the electromagnetic wave encounters a raindrop, part of the electromagnetic energy is absorbed and scattered, producing a difference between the transmitted and received signals. After receiving the reflected wave, the radar compares its phase with the transmitted signal to determine the frequency shift or frequency difference. Analysis of this frequency difference provides the radial velocity of the raindrop.

The radar can also calculate received echo power to obtain precipitation intensity. To achieve more accurate estimates of radial velocity and echo power, radar systems may use multi-frequency transmission and multi-channel reception to improve signal sensitivity and resolution. In addition, TDMA (Time Division Multiple Access) technology can be used to coordinate signals from multiple radar units and improve the accuracy of radial velocity and echo-power estimation.

3.2 Advantages and Disadvantages

Advantages: The equipment is relatively simple and easy to integrate, with good measurement accuracy. It can measure macroscopic cumulative rainfall and rainfall intensity while also capturing microscopic rainfall information, including raindrop size and falling velocity. Miniature radar can additionally detect other weather phenomena such as snow and hail. Low power consumption, low cost, compact size and weight, real-time measurement, and a high degree of automation give miniature radar rain gauges broad application potential.

Disadvantages: It is difficult to accurately measure very small raindrops. With current technical capabilities, the system can generally measure raindrops with diameters above 0.25 mm, which limits its ability to accurately characterize drizzle or very light rain. Under high rainfall intensity, two raindrop signals collected within a short interval can overlap, introducing measurement errors. Wind interference can also increase measurement error.

4. Optical Rain Gauge

When precipitation occurs, hydrometeors affect normally propagating detection light. Instruments that identify precipitation based on optical principles observe rainfall by using a detector to sense and capture precipitation-particle information contained in the detection light. Depending on the recognition method, optical detection can be broadly divided into two approaches: light-intensity attenuation and light scattering. These approaches correspond to disdrometers and forward-scattering visibility/rain sensors, respectively.

4.1 Disdrometer

A disdrometer uses the light-intensity attenuation principle. It detects the attenuation of the measurement light caused by precipitation particles and measures particle fall speed and size. A parallel sheet of light emitted by the light source serves as the detection beam. The beam is thin and wide and, after passing through the detection zone where precipitation particles are falling, is focused onto the receiver.

As precipitation particles fall through the detection zone, they partially block the light sheet, causing the detector output to attenuate and generate a pulse signal. The magnitude of attenuation is related to particle size, while fall speed is related to the time required to pass through the sampling area. By obtaining the pulse signal generated by particles in the detection zone and the time required to pass through that zone, particle size and fall speed can be determined.

Figure 5. Optical attenuation measurement principle. Source image: 

As shown in the figure, (a) illustrates a particle partially blocking the light beam and causing a pulse signal at the detector output, as shown in (b). The pulse width and drop can be used to obtain the time t required for the particle to pass through the sampling zone and the maximum pulse drop Umax. After signal conversion, amplification, and filtering, as shown in (c), the falling pulse is processed by an algorithm to obtain the effective particle diameter d and velocity v.

4.2 Scattering-Type Rain Gauge

The optical scattering method measures precipitation particles by exploiting their scattering of visible or near-infrared light. It is mainly based on the theories of light diffraction and Mie scattering. In operation, a collimated and expanded laser beam illuminates the particle field to be sampled. When the light strikes a particle, scattering occurs. One or two receivers collect the scattered signal generated by precipitation particles, producing digital signals corresponding to the particle size distribution. After optimization and processing, the particle-size distribution of falling particles in the detection zone can be obtained.

Figure 6. Optical scattering measurement principle. Source image: 

Based on these two optical scattering theories, the measurement principles generally apply to relatively small precipitation particles. When particle size becomes larger, analysis based on optical scattering should also be combined with geometric optics.

4.3 Advantages and Disadvantages

Advantages: Optical rain gauges are also known as real-time weather phenomenon sensors. Their key characteristic is a high level of integration, enabling relatively detailed monitoring of microscopic rainfall processes such as raindrop size and fall velocity. The equipment is lightweight, easy to install, highly automated, and relatively low in maintenance cost. It can also identify other weather conditions such as fog and haze, and can recognize seven precipitation types: rain, freezing rain, drizzle, sleet, snow, and hail.

Disadvantages: The biggest disadvantage of optical rain gauges is their high equipment cost, which makes widespread adoption and deployment more challenging.

5. Comparative Analysis of Advantages and Disadvantages

5.1 Macroscopic Measurement vs. Microscopic Measurement

Tipping-bucket rain gauge: strong in macroscopic measurement, weak in microscopic measurement.

The trade-off is clear: its simple structure, high reliability under conventional rainfall conditions, high accuracy, and broad applicability come at the cost of sacrificing the ability to monitor the microscopic physical characteristics of rainfall, including raindrop size, velocity, and size distribution.

In this dimension, the tipping-bucket design forms a direct trade-off with the other three technologies: choosing a mature, high-accuracy solution for large-scale deployment means giving up detailed information about rainfall microphysics.

Piezoelectric, miniature radar, and optical rain gauges: capable of both macroscopic and microscopic measurement.

All three can provide microscopic information, but they continue to make different trade-offs in other dimensions.

5.2 Mechanical Structure vs. Electronic/Optical Sensing

Tipping-bucket (mechanical structure):

Trade-off: The mechanical structure brings inherent disadvantages, including susceptibility to corrosion, sediment accumulation, wear of moving components, and the need for regular manual inspection, maintenance, and servicing. This is one of the fundamental differences between tipping-bucket gauges and the other three technologies, which are static sensing systems.

Piezoelectric, miniature radar, and optical (electronic/optical sensing):

Trade-off: These technologies have no moving parts and can reduce maintenance requirements, giving them greater potential for wear resistance and long-term stability. This benefit, however, comes with trade-offs such as lower measurement accuracy in some conditions, higher cost, and greater electronic complexity.

5.3 Interference Immunity vs. Measurement Accuracy and Information Content

Tipping-bucket:

It is relatively insensitive to electromagnetic interference and raindrop size, but is strongly affected by external natural factors such as leaves, sediment, wind-driven splash, evaporation, and similar influences.

Piezoelectric and miniature radar:

These technologies share a very similar weakness: susceptibility to strong wind. Both are based on dynamic principles—measuring raindrop impact or electromagnetic-wave reflection—so wind can alter raindrop fall velocity and trajectory and directly introduce measurement error.

This creates a trade-off: choosing a method that can measure raindrop velocity and size also means accepting greater sensitivity to wind interference.

Optical rain gauge:

Its optical path can be affected by vibration caused by strong winds and by contamination of optical surfaces, such as dust or water droplets. However, it is generally not directly affected by changes in raindrop dynamics caused by wind.

This creates a more complex trade-off: the optical approach offers theoretically more precise and information-rich measurements, but requires a cleaner operating environment and has the highest equipment cost.

5.4 Cost and Technology Maturity

Tipping-bucket:

Trade-off between maturity and cost: this is the most mature technology, with high accuracy, low cost, and the widest adoption. The trade-off is a relatively high level of manual maintenance required during operation.

Piezoelectric / miniature radar:

These technologies occupy an intermediate position, seeking a balance among cost, functionality, and performance.

Optical:

Trade-off between performance and cost: optical systems provide advanced microscopic monitoring capabilities and multi-weather-phenomenon recognition, but this comes at the highest equipment cost.

5.5 Summary Comparison Table

6. Conclusion

The advantages and disadvantages of these rain gauges do not exist in isolation. Instead, they form a typical technology trade-off:

1. At one end is the tipping-bucket rain gauge: low cost, high reliability, but limited information content.

2. At the other end is the optical rain gauge: higher cost, but rich microscopic rainfall information.

3. In the middle are piezoelectric and miniature radar rain gauges. They attempt to balance cost, functionality, and performance, using moderate cost and a certain level of technical complexity to obtain the ability to detect microscopic rainfall processes, while also introducing new challenges such as sensitivity to wind.

Therefore, tipping-bucket, piezoelectric, miniature radar, and optical rain gauges each have their own advantages and limitations and are suitable for different rainfall monitoring scenarios. Choosing a rain gauge is essentially a matter of matching the measurement technology to the application scenario, budget, and required measurement accuracy. In other words, the decision is about which limitations you are willing to accept in exchange for the advantages that matter most to your application. There is no single "best" rain gauge—only the rain gauge that is best suited to your requirements.

7. Relevance to HONGYUV Weather and Environmental Monitoring Solutions

For field meteorological monitoring, rainfall measurement is rarely an isolated requirement. Rainfall data are often combined with temperature, humidity, wind speed and direction, atmospheric pressure, visibility, radiation, and other environmental parameters to support complete situational awareness.

HONGYUV Technology focuses on the independent R&D and manufacture of meteorological and traffic-environment monitoring instruments. Its product portfolio includes automatic weather stations, integrated weather stations, mobile and portable weather stations, ultrasonic wind sensors, visibility sensors, road-condition monitoring equipment, and other environmental sensing products. The company's website also highlights applications in meteorological and environmental monitoring, transportation weather, agriculture, power and energy, and research-oriented scenarios.

For an integrated weather station, the choice of rainfall sensing technology should therefore be evaluated together with the deployment environment, expected rainfall intensity, required temporal resolution, maintenance conditions, power availability, communication architecture, and the overall data requirements of the application.

In traffic-weather monitoring, for example, precipitation measurements can be combined with visibility and road-state information to support monitoring of low-visibility events, road icing, standing water, snow, and other weather-related risks. In agricultural and hydrometeorological applications, rainfall measurements can complement other meteorological parameters to support irrigation, water-resource management, flood monitoring, and field observation.

HONGYUV also provides OEM/ODM and customized product capabilities. For projects with specific integration requirements, the rainfall sensor can be considered as one module within a broader meteorological sensing system, allowing the overall configuration, interfaces, communications, power supply, and application-specific functions to be matched to the customer's deployment needs.

8. Practical Selection Guide

The following simplified guide can be used when selecting a small rain gauge for a particular application:

• Choose a tipping-bucket rain gauge when low cost, mature technology, straightforward cumulative rainfall measurement, and large-scale deployment are the main priorities.

• Consider a piezoelectric rain gauge when compact integration, low power consumption, real-time response, and microscopic raindrop information are important.

• Consider a miniature radar rain gauge when non-contact precipitation detection, compact design, low power consumption, and additional precipitation-phenomenon sensing are important.

• Choose an optical rain gauge when detailed rainfall microphysics and multi-weather-phenomenon recognition justify a higher equipment cost and stricter optical-surface cleanliness requirements.

• For integrated automatic weather station projects, evaluate the rain gauge together with the other sensing modules and the actual environmental and system requirements rather than selecting it as a standalone component.

9. Related HONGYUV Resource

Related topic: Rain Gauge, Rainfall Collector, Piezoelectric Rain Gauge, and Radar Rain Gauge
https://www.hongyuv.com/index.php?s=tag&name=yuliangtongyuliangjiyadianyuliangjileidayuliangji