Diode Laser Hygrometer (DLH)
Fast water vapour sensing
The Diode Laser Hygrometer (DLH) is a NASA developed, open-path, fast water vapour sensing instrument using a modulated laser around 1.4 μm to detect and quantify atmospheric water vapor. Being open-path the measurement is truly in-situ and absent of any wall or pressure effects of a system with an inlet. The DHL is also fast response for the same reason and can report: water vapor mixing ratio (ppmV), relative humidity with respect to ice relative humidity with respect to ice liquid at up to ~100hz. To achieve this a sensor head with sending and receiving optics will be installed in starboard window 1 and a retroreflector on engine 4, giving a ~13m path length.