Air temperature measurement

A device for measuring ambient air temperature is constructed with a surface part substantially thermally insulated from the interior of the device. This is achieved by providing a layer 3 of thermally insulating foam sandwiched between thin skins 4, 5 of a rigid material forming a housing of the device. Temperature sensors S1 and S2 are disposed respectively just inside the outer thin skin 5 and just inside the inner thin skin 4. By summing suitably weighted outputs from the temperature sensors, the ambient air temperature can be derived independently of the temperature within the housing. Equilibration of the housing and the ambient air temperatures, to avoid the housing acting as a heat sink or source for sensor S1, is therefore not necessary. The derived temperature may be used to correct the output of ultrasonic distance measurements.