Water Vapor, Temperature, and Aerosol Measurements from the New ARM Raman Lidar at Oliktok Point, Alaska

Description

The newest of three Raman lidars operated by the ARM program was installed in September 2014 with the third ARM mobile facility (AMF3) at Oliktok Point, Alaska (70° 30' N, 149° 53' W). This system represents one of only three Raman lidar systems worldwide currently operating in the Arctic as far as we are aware. The design of the Oliktok system is similar to the other ARM Raman lidars in that it transmits at 355 nm and incorporates nine detection channels for measurement of elastic backscatter and Raman backscatter due to vibrational transitions in atmospheric H2O (at 408 nm) and N2 (at 387 nm), and rotational transitions in O2 and N2 (at 353 nm and 354 nm). Simultaneous measurements of analog voltage and photon counts from the photomultiplier tubes are recorded with a height resolution of 7.5 m and a temporal resolution of 10 s. Analog voltages and photon counts are merged through a process called “gluing” to produce photon counting rate profiles for each detection channel. These merge signals are then used to compute various value-added data products (VAPs) such as water vapor mixing ratio, temperature, aerosol backscatter, aerosol extinction and linear depolarization ratio. This poster presents the first VAP results from the new Raman lidar at Oliktok Point. Uncertainties in the VAPs are estimated by propagating the contribution of shot noise in the photon counting data, and comparisons with radiosonde data are performed in order to estimate measurement accuracy. Water vapor retrieval and calibration are challenging due to the dry arctic atmosphere and the persistent low clouds. Varying degrees of spatial and temporal averaging are applied in an effort to enhance detection of the very weak Raman returns in the H2O channel.