Road Weather Sensors

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Road Weather Sensors

• Road Weather, Vaisala Solutions
• Taisto Haavasoja

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Concept of Ice Warning and Prediction on Highways
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Road Weather Station

• Monitors
• road surface conditions
• e.g. icy, wet, dry
• road temperature
• road weather conditions
• precipitation
• air temperature, humidity, dewpoint
• wind, pressure, etc.
• Warns of
• icy road surface
• frost or precipitation

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Typical Sensors in a Road Weather Station

• Atmospheric sensors
• air temperature, humidity, dew point
• precipitation, present weather
• wind speed and direction
• pressure, radiation, ...
• Road sensors
• surface temperature
• surface condition
• ice, water, snow and how much
• salt amount, concentration, depression of
  freezing point (DFP)

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Road Surface Sensors in Testbed

• Road Surface Condition Sensor DRS511
• surface temperature
• surface condition
• salt amount, salt concentration and
• depression of freezing point
• Road Surface Temperature Sensor DST111
• infrared remote thermomometer
• Road Surface Condition Sensor DSC111
• optical detection of ice and snow or frost

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Vaisalas Road Surface Condition Sensor DRS511
Measurement of Conductance and Polarization
Black Ice Detection
Optical Measurement of Layer Thickness
Surface Temperature
DRS511 Multi-Sensor Block
Ground Temperature
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DRS511 Coverage Detection

• Optical coverage detection is based on three
  fibre optics one is transmitting and two are
  receiving.
• The two reflected signals determine the water
  layer thickness (in mm) or the presence of snow
  on the sensor.

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Salt Amount, Concentration and DFP

• Most common deicer is still rock salt (mostly
  NaCl)
• occasionally also CaCl2 is used
• Salt amount (s) is measured in grams per square
  meter (g/m²)
• Water or ice layer thickness (t) is measured in
  millimeters (mm)
• 1 mm of water equals to 1 kg/m² 1 liter/m²
  1 mm m²/m² 1 mm
• We get salt concentration as c s/t
  (g/m²)/mm s/t g/l
• Depression of freezing point DFP f(c)

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Depression of Freezing Point
1. DFP
2. Surface becomes slippery here
3. All liquid frozen
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New Approach to Road Weather Remote Sensing
Surface Condition
Surface Temperature
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Vaisala Remote Road Surface Temperature Sensor
DST111

• Properties
• remote sensor, no installation in the road
• measures also under heavy traffic
• measures also air temperature and humidity
• accurate remote road surface temperature
  measurement
• unique compensation of reflection errors
• estimated accuracy of surface temperature
• 1 C within -20 ... 10 C and with solar
  radiation lt 200 W/m²
• about 0.3 C in typical icing conditions

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Vaisala Remote Road Surface Condition Sensor
DSC111

• Properties
• surface condition
• dry, moist, wet
• snowy/frosty, icy, or slushy (wet snow)
• independent measurement of
• water, ice and snow/frost layer thicknesses
• friction
• slipperiness is output as a friction coefficient
• easy installation and service
• no asphalt cutting, easy traffic control
• measures reliably even under heavy traffic
  conditions

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DSC111 Performance in Freezing Drizzle 09.01.2006
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DSC111 installed in a car
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Highway 3, Helsinki 06.03.2006
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Ring Road 3, Helsinki 06.03.2006
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Side Road in Helsinki 06.03.2006
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DSC111 Friction compared to Actual Measured Values
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Summary

• Effective winter maintenance will result
  increased safety with reduced costs
• Road weather information system is the key
  component in achieving that target
• Vaisala is the world leader in road weather
  systems
• Vaisalas unequaled Remote Road Surface Condition
  Sensor DSC111 measures friction coefficient
  reliably
• look at further details in
• Proceedings of the SIRWEC 2006, page 13.
• http//www.vaisala.com/
• http//www.vaisala.com/weather/dsc111