HWV
Harvard Water Vapor

Harvard Water Vapor (HWV) is an in situ airborne hygrometer developed at Harvard University that measures water vapor mixing ratios in the upper troposphere and lower stratosphere. HWV consists of two instruments with distinctly different methods for detecting water vapor: the Lyman-α photo-fragment fluorescence instrument (LyA) and a tunable diode laser direct absorption instrument (HHH -Harvard Herriott Hygrometer). By combining both instruments, HWV can identify and limit systematic errors while in flight. It provides measurements of water vapor mixing ratio from 1 to 1000 ppmv at a frequency of 1 Hz and with an accuracy of 5%.