Climate and weather affect a vast range of human endeavours, and their importance ranges from convenience and comfort to matters of life and death.
Meaningful climate studies depend critically on measurements, uncertainty of these and correct interpretation. Users of weather data increasingly need uncertainty information, so that they can assess weather-related risks. Humidity and temperature are key variables.
Despite long-term development of techniques, weather-station observations of air temperature and humidity remain challenging. Thermometers and their screens are particularly affected by solar radiation, and relative humidity sensors can drift significantly in condensing conditions. In the upper atmosphere, problems are exacerbated, as balloon-borne sensors additionally need fast response in low-density air. Non-contact measurement methods offer the potential to address all these challenges.