Operating Manual V 3.3 / 9 Dec 2019
MARWIS-UMB
4 Equipment description
In accordance with the demands on road traffic meteorological network sensors are mounted on
vehicles. MARWIS-UMB for the detection of water, ice, snow and friction can be installed on
vehicles. The distance between the sensor and the road must be either 0.5, 1 m or 2 m (1 ¾ ft ,
3 ¼ ft or 6 ½ ft). The STARWIS-UMB must be installed at a distance of 5.5 m (18 ft) to the
ground.
The device works with infrared measuring. Four emitting and two receiving diodes capture the
reflecting behaviour of the road surface at varying wave lengths. Due to the different spectral
properties of various substances – e.g. water and ice – the road state can be deduced from the
captured values.
MARWIS-UMB delivers values for road temperature, dew point temperature, ambient
temperature and humidity, relative humidity at road temperature, water film height, road state,
ice percentage and friction. STARWIS-UMB delivers the same variables except ambient
temperature and humidity.
With an increasing number of ice particles on the road surface the friction coefficient falls and
can thus be of important help when deciding about preventive gritting.
Due to the open interface protocols, MARWIS-UMB as well as STARWIS-UMB can be easily
integrated into existing winter maintenance monitoring networks. Similarly, MARWIS-UMB can
communicate directly with the control system of gritting vehicles.
The measurement data output supports the following protocols: UMB binary.
4.1 Road surface temperature
The road surface temperature is measured with a non-invasive pyrometer which is fullly
integrated into the sensor.
4.2 Ambient temperature
The ambient temperature is the air temperature which is measured by the sensor on the side of
the MARWIS-UMB.
4.3 Relative humidity
Relative humidity indicates the degree to which the air is saturated with water vapour. It changes
with temperature since hot air can absorb more vapour than cold air.
4.4 Dew point temperature
The dew point temperature is the temperature where the current partial water vapour pressure
equals the saturated vapour pressure, which means that condensation sets in e.g. in the form of
fog.
4.5 Relative humidity at road temperature
The calculation of the relative humidity at road temperature is based on the absolute humidity
and the road temperature. It can be used as an indicator for impending formation of dew or
hoarfrost.
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Chapter 4, Equipment description
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