Hail Sensor

HailSens is an advanced sensor system for monitoring hail events in real-time. The detection of hail impacts (as opposed to other types of icy or watery precipitation) relies on vibration measurement. HailSens provides accurate, reliable results both quickly and automatically. A practical tool that saves time and prevents false measurements.

HailSens' large measurement surface (0,2 m²) and piezo-based measurement technique enables the never-before possible ability to investigate high-resolution, real-time details of hail storm dynamics. HailSens enables numerous applications such as on-the-ground validation of hail detection (to optimize weather radar forecast or to add value to data provided by lightning protection networks), early warning system ensuring preventative protection, real-time control of mobile infrastructure parts (closing open roof of a sports stadium, alerting drivers on a highway, closing shutters, turning solar panels into upright position, etc.), recording of individual hail impacts.

HailSens saves data, transfers it in real-time to evaluation software for statistical evaluations and display of impact results in graphics and tables, and - last but not least - provides early warnings using web technology.

HailSens is available either as standalone unit R&D/INS or as the sensor SYNOP integrated in an automatic weather station.

  • Dimensions:
    • Sensor disc (round): Ø 500 mm (19.685“)
    • Ground plate: 500 mm x 500 mm x 10 mm (L x W x H)
  • Mass:
    • approx. 15 kg
  • Operating conditions:
    • Temperature: 0 - +50°C operational temp.
  • Power Requirements:
    • Supply Voltage: 12V – 18V, by solar module and battery or a power supply connection
    • Consumption: 65mA @ 12V (0.8 W)

Is there practical experience with the hailsensor?
Practical experience has been collected for more than a year with a total of 20 hail sensors in Germany and Switzerland.

What is the measurement range of the hail sensor?
Standard measurement range:
The standard measurement range extends from hailstone sizes from 5 mm up to 50 mm with a statistical measurement accuracy of +/- 20%. This information applies to hail sensors of any age, if each sensor is correctly calibrated before each hail season.
Extended measurement range:
Extended measurement ranges are possible upon customer request. Please contact us!

Is bird protection available for the pluviometer?
Faults due to bird pecking do occur but are rare. In most cases, such incorrect measurements occur under meteorological edge conditions, which are untypical for hail showers, and are therefore easy to recognize. A web camera is a good addition to identify unwanted mechanical influences and thus to eliminate incorrect measurements.

Can/must the surface be heated?
Surface heating is not provided for and is not necessary according to general experience. Hail precipitation accompanies thunderstorms, which develop from damp-warm air masses – not with low air temperatures required for snowfall.

Is the measurement influenced by vibrations from other sources?
As with any measurements, when using the hail sensor, external disturbances must also be excluded. Mechanical vibrations transmitted through the ground, through unstable mounting platforms (e.g. caused by winds), or caused by mechanical impacts on the vibration surface of the sensor must be avoided. The influence of ground vibrations, for example, from passing trucks, is rather unlikely, since only the typical frequency range for hail strikes is evaluated in the hail sensor. Incorrect measurements are more likely to be caused by impacts on the sensor surface (measurement surface), such as those triggered by pecking birds, small stones/gravel blown by very strong gusts of wind, or by small animals with hard pointed hooves (e.g. Goats) when climbing over the sensor.

Mounting and positioning:

  • Is ground mounting possible?
  • Why is the sensor mounted on an angle on its mounting bracket? How does the angle of inclination influence the measurement?
  • Must the hail sensor mounting bracket be level?
  • Does elevated mounting, for example on stands or on a measuring container roof, influence measurement accuracy?
  • Is the orientation of the sensor surface important for the correct measurement? What if the hail comes from the side facing away from the tilted sensor?
  • Hail sensors can be mounted on the ground, but they should be protected against small animals (e.g., by a fence that lets hail pass through) to avoid incorrect measurements.
  • The mounting bracket provides an angle of 10° to ensure hailstones slide off. Between angles of 10° and 33°, prototype tests revealed no influence on measurement accuracy. This also means that the hail sensor mounting bracket does not have to be perfectly level. The sensors must be calibrated on site. The mounting position will implicitly be taken into account.
  • Elevated mounting has no effect on measurement accuracy as long as a stable, unchanging position during operation is ensured (i.e., even during thunder storms).
  • Ideally, the inclined sensor surface will point in the direction from which thunderstorm typically approach. The angle of inclination and angle of impact have no significant influence on the accuracy of the measurement: hail impacting from the side that is slanted away is also recorded.
    (Information for these questions is based on 20 measurements in 3 different sensor positions.)

Does the impact angle of the hailstones influence the measurement? In the presence of wind, the hail impact can deviate significantly from the vertical.
The measurement accuracy of 20% relative to the -> standard measurement range is not significantly impaired, as long as the impact angle is within the above-mentioned mounting angle range.

Distance rules from obstacles (hedges, tree rows, houses, etc.): is there a distance rule, for example, which depends on obstacle height?
The recommendation is to mount the hail sensor as much in the open as possible. Buildings, measurement containers, hedges or trees can have a shielding effect. The prevailing wind direction and general orography must be taken into account when choosing a location.

Does the hail sensor have its own internal time reference?
If YES, how accurate is this clock and how and with what is it synchronized?
If NO: Where is the time recorded/the time stamp determined?
With what timing accuracy can the start and end of a hail shower be recorded?

The hail sensor is not equipped with its own clock. Time information is recorded in the data collection equipment with the precision of the clock installed there. It is recommended to periodically synchronize the data collection clock with a precise reference time. For the current prototype generation, data is collected on a local PC with the HASE software.

Is the hail sensor equipped with its own data collector?
For the current prototype generation, data is collected on a local PC with the HASE software.

Can the hail sensor be operated self-sufficiently at locations that are difficult to access? Is there wireless data transmission for this? (GPRS)
Second-generation self-sufficient hail sensors are currently in development. For the current generation, the use of a GPRS modem in the local data collection equipment is recommended.

Is data output only during a hailstorm?
Can the hail sensor be operated in push mode and only send data during an event?
Is it possible to periodically send an empty file – to show that the sensor is active?

The hail sensor only transmits data at the time of an event, e.g. it operates de facto in push mode.
Every 24 hours, a watchdog function simulates a hail impact and tests whether the software still works. A heartbeat file is sent every morning at 01:00 a.m. – a sign the sensor is active.
Alarms in case the connection between the software and sensor is interrupted, as well as the sending of the Heartbeat file, can be deactivated if necessary.

Are there reliable data from recorded precipitation events?
In cooperation with MeteoSchweiz, the hail measurements were recorded and compared with weather radar data.

What form do the data have that the hail sensor outputs via its RS-232 interface?
Data is output as text strings (ASCII code).
Example: For the text string "102mic95", the front number represents the value of the upper plate and the rear number represents the value of the lower plate.

How is the hail sensor calibrated?
A calibration can easily be performed on site. Commercially available metal balls of different diameters are used for this. A calibration kit is being prepared. The procedure is described in the manual.

Aging: Change in response due to weathering.
Aging and weathering processes of the vibration surfaces made of Makrolon and the built-in piezo-electric microphones can lead to a measurement deviation of approximately 10%. On a semi-annual basis (corresponds to the length of a normal hail season), this lies within the specified measurement accuracy of +/- 20 %.
Recommendation: Calibrate the hail sensor before the start of each hail season in order to best compensate for the effects of weather and aging.

What data does the HASE software generate?
The software processes the sensor data to extract the following information:

  • Time stamp
  • Kinetic energy of the impact
  • Impulse of the impact
  • Hail class of the impact

From the values listed above, it is possible to derive the velocity and hailstone size using the formula for impact velocity.

Why is the sensor shaped like an octagon? How was the size of the sensor plates chosen?
The dimensions of the sensor plate are derived from oscillation physics and were chosen to ensure a statistically significant measurement. For the current pilot generation, the octagonal shape was chosen as an approximation to a round shape in order to avoid a change in the stiffness of the vibration surface at angles of less than or equal to 90°. Future generations of hail sensors will more closely approach the circular shape.

For which applications can the hail sensor be used? Can hail sensors also be combined with other systems?
Combined with weather radars, the hail sensor allows the reliable measurement and prediction of hail events. The type of ground precipitation cannot be determined from radar images. The in-situ measurements with the hail sensor provides significantly more complete information. Equipment and systems can be controlled using measurement data from the hail sensor, for example, rolling shutters, sports arena roofs or solar power systems. Conversely, local measurements of air temperature, relative humidity and air pressure help assure the quality of hail measurements.

What are the main advantages of the hail sensor?

  • Electronic sensing of data enables their online transfer
  • Early warning of hail incidents: Real-time evaluation ensures time to take steps
  • Hail incidents can be clearly mapped in time
  • Recording of hail intensity
  • Long-term use across a great many precipitation events is easily possible

Benefit 1: Online Autonomous Monitoring Device

  • low-power, wireless data transmission
  • low infrastructure & maintenance costs

Benefit 2: Real-Time Control & Early Warning

  • damage control: roller shutter, retractable roof, tracking solar panel
  • lead time to take protective measures

Benefit 3: Documentation of the Hail Event

  • add proper documentation to damage claims
  • hailstorm event assessment + filed claims validation

Benefit 4: Improved Data Products

  • prognostic models: calibration with real data
  • weather radar/lightning protection: hail cell identification
  • Hail storm warnings.
  • Hail research.
  • SYNOP/METAR icy precipitation measurement.
  • Recording and evidence production of hail storm event.

Application Areas:

  • Weather services
  • Insurance companies
  • Universities, research institutes
  • Solar system operators
  • Agriculture
  • Civilian and military aviation
  • Automotive sector
  • Industry and commerce