Krypton Hygrometer

Fast-response hygrometer operating on the principle of absorption of ultraviolet light in a band generated by excitation of krypton gas.  Used in combination with a three-component sonic anemometer to measure latent heat flux.  Very low power consumption, but the signal drifted as the sensor developed an invisible "scale", especially in high humidity.  Also, early versions had issues with rain penetrating both the head and the electronics box that required component replacement.  Finally, both source and detector tubes became problematic for CSI to manufacture.  ISFS has surplussed the ones that we had and now used the Campbell EC-150 for this measurement (also carbon dioxide), albeit with higher power consumption.