University of Colorado Total Water Measurement

This measurement is made with a closed-path tunable diode laser hygrometer (CLH), based on the water vapor hygrometers
designed by R. D. May (Maycomm, Inc.). CLH is coupled to a heated, forward-facing inlet that enhances
particulate water by anisokinetic sampling. Ice water content (IWC) is derived from the measurement of enhanced
total water, with knowledge of the instrument sampling characteristics, particle size distributions and ambient water vapor.

The CLH is small, lightweight and power-efficient (see table below).

In contrast to the open-path systems of similar heritage, the CLH, which was designed for operation in the troposphere on commercial aircraft, has a single-pass absorption cell (27.62 cm long). The light source is a room-temperature solid-state laser that puts out 3-5 mW of radiation at 1.37 mm (7306.752 cm-1).

Instrument Details:

Dimensions 20" x 10" x 6"
Weight 21 lbs.
Power (exclusive of structural heaters) 25 W
Response Time 125 msec (8 Hz)
Accuracy of water vapor (2s) 5-10%
Accuracy of ice water content (2s) 20%
Location right wind pod


The CLH instrument has flown in the right spear pod of the WB-57F during CRYSTAL-FACE, MidCiX and PUMA missions,
measuring IWC in various types of cirrus clouds and in the exhaust plumes of several rockets and the Space Shuttle.

Installing CLH in the wingpod of the WB57F during PUMA-A


S. M. Davis, A. G. Hallar, L. M. Avallone, and W. Engblom, 2007, Measurements of ice water content with a tunable diode laser hygrometer: Calibration procedure and inlet analysis, J. Atmos. Oceanic Technol., 24, 463, doi:10.1175/JTECH1975.1.

S. M. Davis, L. M. Avallone, E. M. Weinstock, C, H. Twohy, J. B. Smith, and G. L. Kok, 2007, Comparisons of in situ measurements of cirrus cloud ice water content, J. Geophys. Res., 112, D10212, doi:10.1029/2006JD008214.