In outdoor water level monitoring — rivers, reservoirs, urban flood points, or pumping stations — one question persists: Is the sensor reliable during heavy rain?
Laser and ultrasonic sensors fail in storms. Laser signals attenuate over 70% under heavy rain (>30mm/h). Ultrasonic sensors suffer false alarms and signal loss.
The answer: Millimeter-wave (mmWave) radar — including 24GHz radar, 77GHz radar, and high-frequency 80GHz/120GHz radars. As a versatile radar sensor, mmWave technology proves itself in the harshest weather.
This article analyzes mmWave radar’s real-world performance for water level monitoring in heavy rain.
I. Three Challenges Heavy Rain Creates for Sensors
Challenge 1: Raindrop blocking
Raindrops scatter or absorb signals. Laser range drops >70%; ultrasonic false alarms increase 5x.
mmWave response: A 24GHz FMCW radar or 77GHz radar experiences <5% attenuation — raindrops are much smaller than electromagnetic wavelengths.
Challenge 2: Water surface fluctuation
Wind-driven waves cause traditional sensors to mistake peaks for actual water levels.
mmWave response: High-frequency radars (80/120GHz) offer narrow beams and high resolution. Even a 24GHz Doppler radar sensor effectively tracks moving surfaces.
Challenge 3: Lens contamination
Rain + sediment coats optical lenses and ultrasonic membranes.
mmWave advantage: No optical window — the antenna is sealed in a radome. This makes microwave radar sensor technology inherently robust for outdoor use.
II. Four Real-World Advantages of mmWave Radar
Advantage 1: Rain penetration — physical superiority
Whether using 24GHz radar, 77GHz radar, or a 24GHz Doppler radar sensor, signal attenuation under heavy rain is <5% — versus >70% for laser.
Advantage 2: Intelligent surface tracking with FMCW
A 24GHz FMCW radar provides continuous wave modulation for precise distance measurement, enabling:
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Water surface vs. clutter discrimination (banks, debris)
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Average water level output (not wave peaks)
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Anti-multipath interference
80/120GHz radars add millimeter-level resolution to distinguish floating debris from actual water.
Advantage 3: Maintenance-free operation
Sealed antenna design means zero performance degradation after weeks of heavy rain. The same microwave radar sensor principles apply to radar flowmeter and velocity flow monitor applications.
Advantage 4: High-frequency (80/120GHz) benefits
| Band | Beam Angle | Resolution | Best For |
|---|---|---|---|
| 24GHz | 8-12° | cm-level | Basic level, 24GHz Doppler radar sensor |
| 77GHz | 4-6° | cm-level | Auto/level, 77GHz radar |
| 80GHz | 3-5° | mm-level | High-precision, narrow channels |
| 120GHz | 2-3° | mm-level | Precision measurement |
III. Beyond Level: Flow and Velocity Monitoring
mmWave radar extends beyond water level. A radar flowmeter uses Doppler shift to measure surface flow velocity non-contact. A velocity flow monitor combines level and velocity data to calculate volumetric flow rate.
In heavy rain, a 24GHz FMCW radar or microwave radar sensor simultaneously measures:
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Water level (via FMCW ranging)
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Surface velocity (via Doppler shift)
This makes mmWave radar a complete radar sensor solution for open-channel flow monitoring — impossible with laser or ultrasonic in rainy conditions.
IV. Performance Comparison
| Scenario | Laser | Ultrasonic | mmWave Radar |
|---|---|---|---|
| Light rain | Usable | Usable | Stable |
| Moderate rain | Attenuation | False alarms | Stable |
| Heavy rain | Fails | Fails | Stable |
| Flow velocity | Not possible | Not possible | Doppler-capable |
V. Deployment Case
Urban flood monitoring: A southern city replaced ultrasonic sensors with 80GHz mmWave radar at low-lying underpasses. During Typhoon “Fireworks” (200mm rain/day), results were:
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Continuous, stable water level data
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Zero false alarms
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6 months operation without cleaning
The site later added a radar flowmeter and velocity flow monitor using 24GHz FMCW radar — all performed flawlessly in subsequent storms.
VI. How to Choose?
| Application | Recommended Sensor |
|---|---|
| Basic level monitoring | 24GHz radar or 24GHz Doppler radar sensor |
| High-precision level | 77GHz radar or 80GHz |
| Flow (level + velocity) | Radar flowmeter with 24GHz FMCW radar |
| Complete flow monitoring | Velocity flow monitor + microwave radar sensor |
| Narrow channel / debris | 80GHz or 120GHz |
VII. Summary
Conclusion: In heavy rain, mmWave radar is not just “better” — it is the only reliable non-contact water level sensor.
Whether you need a 24GHz radar for basic level, a 77GHz radar for precision, a 24GHz Doppler radar sensor for velocity, a 24GHz FMCW radar for continuous ranging, or a radar flowmeter / velocity flow monitor for complete flow measurement — mmWave radar sensor and microwave radar sensor technology delivers when lasers and ultrasonics fail.
For rivers, reservoirs, urban flood control, or pumping stations, mmWave radar is the proven heavy-rain solution.
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Want to use radar in your project?
Contact Vivi: susiqi@mwradar.com or WeChat/WhatsApp: +86 181 2377 8519
