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 ratios 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 led to 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

Related Publications


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.


Dzambo AM, DD Turner, and EJ Mlawer. 2015. "Evaluation of two Vaisala RS92 radiosonde solar radiative dry bias correction algorithms." Atmospheric Measurement Techniques Discussions, 8(10), 10.5194/amtd-8-10755-2015.


Cady-Pereira KE, MW Shephard, DD Turner, EJ Mlawer, SA Clough, and TJ Wagner. 2008. "Improved Daytime Column-Integrated Precipitable Water Vapor from Vaisala Radiosonde Humidity Sensors." Journal of Atmospheric and Oceanic Technology, 25(6), 10.1175/2007jtecha1027.1.


Ferrare RA, EV Browell, S Ismail, S Kooi, LH Brasseur, VG Brackett, MB Clayton, J Barrick, GS Diskin, J Goldsmith, BM Lesht, JR Podolske, GW Sachse, FJ Schmidlin, DD Turner, DN Whiteman, D Tobin, L Miloshevich, HE Rivercomb, BB Demoz, and PD Girolamo. 2004. "Characterization of upper-tropospheric water vapor measurements during AFWEX using LASE." Journal of Atmospheric and Oceanic Technology, 21, 10.1175/jtech-1652.1.

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