En-SCI Cryogenic Frost Point Hygrometer

A sonde that accurately and precisely measures water vapor at elevations from the earth’s surface to the mid-stratosphere.


  • Process studies in the upper troposphere and lower stratosphere
  • Measurement of water vapor inside ice clouds
  • Dehydration studies (particularly in the tropical upper troposphere)
  • Validation of satellite measurements and radiosonde humidity sensors


  • Highly sensitive--can measure water vapor at the parts-per-million level
  • Cost effective--avoids the costs associated with aircraft-mounted instruments
  • Simple operation
  • Lightweight with minimal power requirements (allows unit to be launched with small balloons)
  • Able to perform accurate measurements during descent as well as ascent
  • Software included for easy monitoring of the CFH unit
  • Compatible with DMT / EN-SCI ECC ozonesondes

How It Works

The CFH operates by maintaining a small mirror at the precise temperature necessary to generate a thin, constant layer of condesate on the mirror. When this layer exists, the mirror temperature is the same as the ambient frost or dew point temperature.

An LED emits light that is reflected off the mirror, and a photodetector senses this reflected light, which varies with the amount of frost. The photodetector signal is then used to adjust the mirror temperature. The mirror is heated with a heater coil and cooled with cryogenic liquid. These mechanisms allow the mirror to be heated and cooled quickly so that its temperature reflects the current frost or dew point.


Parameter Specification
Measured Parameters Ambient Frost Point
Derived Parameters Relative Humidity, Mixing Ration
Technique Temperature-controlled chilled mirror
Uncertainty Measurement 4% in tropical lower troposphere
10% in middle stratosphere
9% in tropopause
Altitude Range 0 - 25 km (all climates)
Weight < 400 g (without coolant)
Instrument Dimensions 7.6 cm x 7.6 cm x 13.3 cm
Dimensions (in Flight Box) ~12" W x 12" D x 12" H (~39cm x 39cm x 39cm)

Specifications are subject to change without notice.

Included Items

  • CFH sonde(s)
  • Operator manual
  • One-year warranty
  • Email and phone technical support

How to Order

Contact EN-SCI for pricing or more information.

mailicon  info@en-sci.com

infoicon Phone: +303 484 9774

Selected Bibliography

Miloshevich, L. M., H. Vömel, D. N. Whiteman, B. M. Lesht, and F. J. Schmidlin (2006). “Absolute accuracy of water vapor measurements from six operational radiosonde types launched during AWEX and implications for AIRS validation,” Journal of Geophysical Research, 111, D09S10, doi:10.1029/2005JD006083. Link

Oltmans, S. J., and D. J. Hofmann (1995), “Increase in lower-stratospheric water vapour at a mid-latitude Northern Hemisphere site from 1981 to 1994,” Nature, 374, 146– 149. Link

Shibata, T., H. Vömel, S. Hamdi, S. Kaloka, F. Hasebe, M. Fujiwara, and M. Shiotani (2007), “Tropical cirrus clouds near cold point tropopause under ice supersaturated conditions observed by lidar and balloon-borne cryogenic frost point hygrometer,” Journal of Geophysical Research, 112, D03210, doi:10.1029/2006JD007361. Link

Vömel, H., D. E. David and K. Smith (2007). “Accuracy of tropospheric and stratospheric water vapor measurements by the cryogenic frost point hygrometer: Instrument Details and Observations.” Journal of American Geophysical Research, Vol. 12, D08305, doi:10.1029/2006JD007224. Link

Vömel, H., V. Yushkov, S. Khaykin, L. Korshunov, E. Kyrö , and R. Kivi (2007). “Intercomparisons of stratospheric water vapor sensors: FLASH-B and NOAA/CMDL frost point hygrometer.” J. Atmos. Ocean. Technol, Vol. 24, doi: 10.1175/JTECH2007.1. Link