Status
The University of Colorado Closed-path Laser Hygrometer, version 2 (CLH2) is an infrared absorption instrument designed to measure so-called “total water”, the sum of water vapor and particulate water. It is a second-generation sensor that derives from the original CLH and was developed for the NSF DC3 campaign in 2011 as an alternative to the NCAR CVI for measurements of cloudwater contents. It has flown on the NASA DC-8 and the NSF/NCAR G-V and C-130. The most recent campaign was NSF SOCRATES in 2018. CLH-2 uses a fiber-coupled tunable diode laser at 1.37 μm to measure by absorption the water vapor resulting from the evaporation of cloud particles. The spectrometer will be housed in a modified PMS canister and coupled to a heated forward-facing inlet. Sampling of particles is deliberately sub-isokinetic, which results in enhancements of particle mass relative to ambient by factors ranging between 30 and 70. Therefore, condensed water even in very thin clouds can be measured with high precision and accuracy.