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Accurate humidity and air temperature measurements for meteorology and climate

NPL is making a difference to humidity and temperature observations in weather stations

The need

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.

The impact

Recent and current NPL humidity and temperature projects are making a difference by:

  • Providing measurement traceability  for humidity and temperature observations in weather stations across the UK
  • Developing novel measurements, such as non-contact thermometer and hygrometer (NCTAH) to overcome the problems of conventional sensors for ground-based and airborne measurements
  • Improving understanding of humidity observations by studying hygrometer drift in weather stations , quantifying this and highlighting the special interpretation needed in high humidity conditions
  • Addressing the challenge of measuring air temperature  by quantifying temperature errors caused by solar radiation on thermometers
  • Paving the way for sourcing weather data more widely by developing uncertainty analysis  for temperature and humidity observations sourced from third parties
  • Soil moisture work including field measurements and study of calibration needs
  • Working with the World Metrological Organization to contribute to definitive guidance  for meteorological measurements worldwide
  • Working with other NPL science areas  of atmospheric measurement  and earth observation

Read more about humidity & moisture

Read our case study: Better measurements of water vapour in fuel gas