Met 20 and Met 21 Unaspirated Radiation Shields  

These radiation shields are designed to house temperature and humidity probes to protect them from the heating effects of solar radiation and also to protect them from direct exposure to rain and snow. The shields have improved design and performance characteristics compared to similar screens on the market whilst still being relatively low cost.  

All unaspirated radiation shields overheat when solar radiation is high and wind speed is low. Problems are also seen in the winter when the sun’s angle is low or there is reflection off snow. However, the unique design and construction of these sensors is specifically designed to overcome these issues.  

The design of this shield has a white outer reflective surface combined with an inner barrier of non-reflective, black louvres to prevent sunlight reaching the sensor whilst still allowing air to flow through to the sensor. This unique construction is more effective at blocking solar radiation and thus the sensors inside the shield give a more representative reading of the true air temperature and relative humidity. Errors under adverse conditions are typically half those compared to similar shields.  

The shape of the louvres is based on an established design that is in common use in a modern Stevenson screen made by the same manufacturer. That screen is sold to national meteorological services worldwide