cfh: Cryogenic Frostpoint Hygrometer

The cryogenic frostpoint hygrometer (CFH) is a small, balloon-borne instrument that provides highly accurate measurements of water vapor in the atmosphere. The CFH has a significantly greater sensitivity to water vapor than standard radiosondes, as it can measure the frostpoint or dewpoint temperatures at an accuracy better than 0.2 K corresponding to water volume mixing ratio accuracies of only a few parts per million.

The main instrument component is a small mirror, which is cooled by a cryogen in order to be covered with a thin layer of water vapor condensate. A pair of photodiodes detects the condensation on the temperature-controlled mirror. The phase of the condensate is controlled by a force-freezing algorithm, allowing for clear interpretation of the dew point versus frostpoint.

The replacement of analog electronics with a microprocessor, a feedback controller, and thermistor calibration have improved accuracy and performance of the CFH over its predecessors. Further characteristics like reduced power consumption and low instrument weight made the CFH a successful instrument to perform in situ balloon-borne measurements of water vapor in the upper troposphere and lower stratosphere. CFH measurements are now used worldwide to validate radiosonde, satellite, and ground-based profiler measurements.



  • Fixed
  • AMF1
  • AMF2
  • AMF3


Dover J, D Brewer, and M Lataille. 2020. National Weather Service Radiosonde Evaluation Field Campaign Report. Ed. by Robert Stafford, ARM user facility. DOE/SC-ARM-20-001.


Stuefer M and T Gordon. 2018. Cryogenic Frostpoint Hygrometer (CFH) Instrument Handbook. Ed. by Robert Stafford, ARM Climate Research Facility. DOE/SC-ARM-TR-210.


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