Differential absorption hygrometer

{
  "id": "MLC-T-MET-004978",
  "term": "Differential absorption hygrometer",
  "field": "Meteorology and atmospheric science",
  "definition": "An instrument that measures atmospheric water vapor concentration by exploiting the differential absorption of two closely spaced laser wavelengths by water molecules. One wavelength is strongly absorbed by water vapor, while the other is weakly absorbed or not absorbed at all. The ratio of the received signals at these two wavelengths provides a precise measure of water vapor content along the path.",
  "url": "https://mlchart.com/terminology/meteorology/differential-absorption-hygrometer/"
}