Dedicated hail surveillance for size, intensity & damage assessment
HailFlow HF4 is an acoustic impact instrument dedicated to the observation of hail and solid hydrometeors. It detects each hailstone's kinetic energy and classifies stones into 15 size classes from about 0.5 to 8 cm, with no moving parts and extremely robust mechanics.
Ideal for solar plants, wind farms, crops, infrastructure, stations.
- Stainless-steel sensing plate – no optical path to obstruct.
- Insensitive to rain splashes, measures only solid impacts.
- Designed for long-term, zero-maintenance deployment.
Purpose-built for hail risk and damage monitoring
From simple hail detection to detailed size distribution and kinetic energy, HailFlow HF4 delivers high-resolution data for risk analysis and damage assessment.
Hailstorms can severely damage solar plants, crops, wind farms, vehicles and buildings in just a few minutes. Conventional rain gauges, optical sensors or simple impact plates rarely provide the detailed information needed to understand hail intensity, stone size distribution or kinetic energy — all essential parameters for risk modelling, warning systems and post-event damage assessment.
HailFlow HF4 is designed specifically for this task. A plain suspended stainless-steel disk head intercepts each falling hailstone; the resulting vibro-acoustic signal is measured inside a sealed aluminum body using a dedicated microphone and signal-processing chain. For every impact, the instrument estimates the associated kinetic energy and classifies the hailstone into one of 15 nominal size classes, from small hail to large stones above 8 cm in diameter, with a counting capacity of up to about 25 impacts per second.
Extremely robust and fully sealed, HailFlow HF4 is suitable for long-term deployment in severe convective storm regions, including offshore wind farms and isolated infrastructure. The sensor is not sensitive to rain, so liquid precipitation cannot bias hail measurements, which is crucial during mixed rain-and-hail events.
Why HailFlow HF4
HailFlow HF4 is engineered to detect solid hydrometeors through their kinetic energy at impact, not by adapting a rain or optical device for hail. This provides data directly relevant to hail severity, material stress and damage functions for exposed assets.
Internal processing distinguishes between 15 hailstone diameter classes, nominally from 0.5 to 8 cm. Each impact is assigned to a size bin based on calibrated vibro-acoustic amplitude, delivering a complete size distribution for each observation period.
The sensor counts individual impacts up to approximately 25 hits per second, enabling the characterization of very intense hail bursts and cumulative hit counts on PV modules, turbine blades, vehicle surfaces or structural elements.
By design, HailFlow HF4 is not sensitive to rain: liquid precipitation and splashes in the low-energy range do not bias the hail signal. This ensures reliable measurements during mixed precipitation events and under heavy rainfall.
A 200 mm diameter stainless-steel sensing plate, heavy mechanical structures and a sealed aluminum body provide an ultra-robust, zero-maintenance platform for long-term outdoor deployment, including offshore and extreme wind environments.
HailFlow HF4 offers generic analog outputs, SDI-12, serial ASCII, Modbus RTU and 4–20 mA adapters, Cloud Data link interface, enabling straightforward integration into SCADA, PLCs, industrial control systems, environmental dataloggers and moreover any type of standard or custom platforms.
Where HailFlow HF4 makes a difference
HailFlow HF4 supports a wide range of operational and research applications wherever hail is a significant risk factor.
Infrastructure & energy
- Solar plants and PV fields — Monitor hail hit counts and size classes on photovoltaic modules to correlate damage patterns with measured kinetic energy and refine design, shielding and insurance strategies.
- Wind farms (onshore & offshore) — Assess hail exposure of blades, nacelles and towers, including in strong wind and marine conditions, and relate it to surface erosion and maintenance needs.
- Buildings, car parks & industrial sites — Document hail events for structural design feedback, risk mitigation and objective post-event reporting.
Agriculture & crop protection
Vineyards, orchards and crops — Track hail intensity and stone-size distribution over vulnerable areas, support activation of protective measures (e.g. nets, shelters) and provide objective data for insurance claims and loss estimation.
Meteorology & hazard warning
- Convective storm corridors — Provide dedicated hail monitoring in regions exposed to severe storms, feeding nowcasting systems, severe weather alerts and post-event analyses.
- Support validation of radar-based hail detection algorithms with ground-truth size-distribution measurements.
Transport & infrastructure protection
Install along roads, highways, airports and railways where hail can affect operations, equipment and safety, providing objective indicators for operational decisions and maintenance planning.
Research & model validation
Use hailstone size and energy distributions to validate convective storm models, radar-based hail products and impact-modelling approaches in climate and weather research programs.
Acoustic impact & kinetic energy sensing
HailFlow HF4 uses an acoustic vibro-impact principle optimized for hailstone detection and size classification.
- A stainless-steel plate mounted on a damped support intercepts each falling hailstone.
- The impact excites a vibrational response in a sealed acoustic cavity within the instrument body.
- A dedicated microphone and impulse detector convert the vibro-acoustic signal of each impact into a transient voltage peak.
- The maximum amplitude of this peak is linked to the kinetic energy transferred during the impact.
- Using a calibrated linearization model, the instrument classifies each impact into one of 15 nominal hailstone diameter classes and updates cumulative statistics.
What the instrument delivers
- Per-event hailstone counting, including maximum hit rates during storm peaks.
- Size distribution over 15 classes, typically from ~5 mm up to ≥ 75 mm in diameter.
- Derived kinetic energy and hail intensity indicators for each observation period.
Core specifications
Measured & derived parameters
- Number of hailstone impacts (hit count) for each measurement interval.
- Percentage or count of hits in each hailstone size class (15 diameter classes).
- Nominal hailstone diameter associated with each class (~0.5–8 cm range).
- Derived kinetic energy and hail intensity indices based on impact energy.
Performance
- Nominal diameter range: about 0.5 to 8 cm (15 classes covering small to very large hailstones).
- Maximum count rate: ~25 solid impacts per second (≈795 impacts·m⁻²·s⁻¹).
- Insensitive to rain and low-energy liquid impacts, minimizing false hail detections.
- Lifetime factory calibration, no periodic recalibration required under normal use.
Outputs & protocols
- Generic analog voltage outputs (two channels, OUT1 & OUT2, with configurable scaling and variables).
- SDI-12 data interface for easy integration with dataloggers.
- Serial ASCII (RS-422/RS-485 via external converters) for digital integration.
- Modbus RTU RS-485 via optional MOBUS adapter for SCADA and PLC networks.
- 4–20 mA current loops via optional AD420 adapter for industrial process inputs.
- Cloud Data Link interf. (C-LINK)
Power & acquisition
- Low power consumption with configurable acquisition and averaging cycles.
- Supports continuous or duty-cycled operation for solar-powered remote sites.
- Internal datalogger with cyclic or finite recording modes for standalone "black-box" operation.
Mechanical design
- 200 mm diameter, robust stainless-steel plate as sensing head.
- Sealed aluminum cylindrical body with embedded electronics and acoustic cavity.
- Heavy-duty mounting arm with integrated vibration damper to decouple structural vibrations.
- Universal V-bracket mounting for mast diameters from roughly 16 to 82 mm, or any flat or rectangular surface.
- Full 316L stainless-steel sensor and mounting kit for offshore and extremely harsh environments.
WMO conformity & field use
WMO conformity of the HailFlow HF4
HailFlow HF4 is designed in line with World Meteorological Organization (WMO) guidance for solid precipitation and hail observation, as described in the WMO Guide to Instruments and Methods of Observation (WMO-No. 8) and related recommendations for hydrometeor detection, calibration and data exchange (e.g. WMO-No. 49 and WMO-No. 306 BUFR for encoding hail parameters). Its robust construction, traceable calibration and standardized outputs make it suitable for operational meteorological networks, research observatories and national weather services.
Proven in real-world hail damage scenarios
HailFlow HF4 has been developed and validated with users requiring high-resolution traceability of hail damage and extreme events, including: solar plants and PV farms, onshore and offshore wind farms, car parks and vehicle fleets, industrial sites and agricultural areas such as crops, orchards and vineyards.
Across these applications, HF4 has demonstrated long-term reliability, excellent performance during severe convective storms and strong compatibility with modern monitoring architectures and risk-management workflows.
Ready to instrument your sites for high-resolution hail monitoring?
Our team can help you specify sensor locations, configure interfaces and integrate HailFlow HF4 into existing SCADA, datalogger or risk-management platforms. We also support turnkey solutions for solar plants, wind farms, agricultural sites and meteorological networks.