Validation of the Water Vapor Profiles of the Raman Lidar at the Maïdo Observatory (Reunion Island) Calibrated with Global Navigation Satellite System Integrated Water Vapor

Abstract

The Maïdo high-altitude observatory located in Reunion Island (21 ∘ S, 55.5 ∘ E) is equipped with the Lidar1200, an innovative Raman lidar designed to measure the water vapor mixing ratio in the troposphere and the lower stratosphere, to perform long-term survey and processes studies in the vicinity of the tropopause. The calibration methodology is based on a GNSS (Global Navigation Satellite System) IWV (Integrated Water Vapor) dataset. The lidar water vapor measurements from November 2013 to October 2015 have been calibrated according to this methodology and used to evaluate the performance of the lidar. The 2-year operation shows that the calibration uncertainty using the GNSS technique is in good agreement with the calibration derived using radiosondes. During the MORGANE (Maïdo ObservatoRy Gaz and Aerosols NDACC Experiment) campaign (Reunion Island, May 2015), CFH (Cryogenic Frost point Hygrometer) radiosonde and Raman lidar profiles are compared and show good agreement up to 22 km asl; no significant biases are detected and mean differences are smaller than 9% up to 22 km asl.

Effect of deep convection on the TTL composition over the Southwest Indian Ocean during austral summer

“…CC BY 4.0 License. Keckhut et al, 2015;Vérèmes et al, 2019). Laser pulses are generated by two Quanta Ray Nd:Yag lasers, the geometry for transmitter and receiver is coaxial and the backscattered signal is collected by a Newtonian telescope with a primary mirror of 1200 mm diameter.…”

“…The time slot of routine operations is around 19:00 to 01:00 (+1) local time but there are intensive periods of observation during field campaigns that allowed longer measuring span. The Raman lidar water vapor observations were validated during the MORGANE intercomparison exercise in May 2015 (Vérèmes et al, 2019). During the MORGANE campaign, CFH radiosonde and Raman lidar profiles showed mean differences smaller than 9 % up to 22 km asl.…”

Effect of deep convection on the tropical tropopause layer composition over the southwest Indian Ocean during austral summer

“…The CFH was developed to provide highly accurate water vapor measurements in the TTL and stratosphere where the water vapor mixing ratios are extremely low (∼ 2 ppmv). CFH mixing ratio measurement uncertainty ranges from 5 % in the tropical lower troposphere to less than 10 % in the stratosphere (Vömel et al, 2007); a recent study shows that the uncertainty in the stratosphere can be as low as 2 %-3 % (Vömel et al, 2016). However, water vapor measurements in the stratosphere by the CFH can be contaminated by sublimation of water from an icy intake or from the balloon and payload at a pressure lower than 20 hPa (Jorge et al, 2020).…”

“…A Raman water vapor lidar emitting at 355 nm has been operating at the Maïdo Observatory since April 2013 (Baray et al, 2013;Keckhut et al, 2015;Vérèmes et al, 2019). Laser pulses are generated by two Quanta-Ray Nd:Yag lasers, the geometry for transmitter and receiver is coaxial, and the backscattered signal is collected by a Newtonian telescope with a primary mirror of 1200 mm diameter.…”

“…In order to convert the backscattered radiation profiles into water vapor mixing ratio profiles, the calibration coefficient is calculated from water vapor column ancillary data: GNSS (Global Navigation Satellite System) IWV (Integrated Water Vapor). The description of the calibration method and the total uncertainty budget can be found in Vérèmes et al (2019).…”