skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Cryogenic Frostpoint Hygrometer (CFH) Instrument Handbook

Technical Report ·
DOI:· OSTI ID:1427705
 [1];  [1]
  1. University of Alaska, Fairbanks (United States)

The U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility’s Cryogenic Frostpoint Hygrometer (CFH) is a small, balloon-borne instrument that provides highly accurate measurements of water vapor in the atmosphere. The CFH, although highly modified, is based upon the National Oceanic and Atmospheric Administration (NOAA)/Climate Monitoring and Diagnostic Laboratory (CMDL) frostpoint hygrometer (FPH) that has been flown in Boulder, Colorado, since 1980. 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 part 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.

Research Organization:
DOE Office of Science Atmospheric Radiation Measurement (ARM) Program (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
Contributing Organization:
University of Alaska, Fairbanks (United States)
DOE Contract Number:
Report Number(s):
Country of Publication:
United States