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Title: Calibration of Raman lidar water vapor profiles by means of AERONET photometer observations and GDAS meteorological data
Authors: Dai, Guangyao 
Althausen, Dietrich 
Hofer, Julian 
Engelmann, Ronny 
Seifert, Patric 
Bühl, Johannes 
Mamouri, Rodanthi-Elisavet 
Wu, Songhua 
Ansmann, Albert 
Major Field of Science: Natural Sciences
Field Category: Earth and Related Environmental Sciences
Keywords: AERONET;Calibration;Lidar;Measurement method;Mixing ratio
Issue Date: 8-May-2018
Source: Atmospheric Measurement Techniques, 2018, vol. 11, no. 5, pp. 2735-2748
Volume: 11
Issue: 5
Start page: 2735
End page: 2748
Journal: Atmospheric Measurement Techniques 
Abstract: We present a practical method to continuously calibrate Raman lidar observations of water vapor mixing ratio profiles. The water vapor profile measured with the multiwavelength polarization Raman lidar PollyXT is calibrated by means of co-located AErosol RObotic NETwork (AERONET) sun photometer observations and Global Data Assimilation System (GDAS) temperature and pressure profiles. This method is applied to lidar observations conducted during the Cyprus Cloud Aerosol and Rain Experiment (CyCARE) in Limassol, Cyprus. We use the GDAS temperature and pressure profiles to retrieve the water vapor density. In the next step, the precipitable water vapor from the lidar observations is used for the calibration of the lidar measurements with the sun photometer measurements. The retrieved calibrated water vapor mixing ratio from the lidar measurements has a relative uncertainty of 11% in which the error is mainly caused by the error of the sun photometer measurements. During CyCARE, nine measurement cases with cloud-free and stable meteorological conditions are selected to calculate the precipitable water vapor from the lidar and the sun photometer observations. The ratio of these two precipitable water vapor values yields the water vapor calibration constant. The calibration constant for the PollyXT Raman lidar is 6.56 g kg-1 ±0.72 g kg-1 (with a statistical uncertainty of 0.08 g kg-1 and an instrumental uncertainty of 0.72 g kg-1). To check the quality of the water vapor calibration, the water vapor mixing ratio profiles from the simultaneous nighttime observations with Raman lidar and Vaisala radiosonde sounding are compared. The correlation of the water vapor mixing ratios from these two instruments is determined by using all of the 19 simultaneous nighttime measurements during CyCARE. Excellent agreement with the slope of 1.01 and the R2 of 0.99 is found. One example is presented to demonstrate the full potential of a well-calibrated Raman lidar. The relative humidity profiles from lidar, GDAS (simulation) and radiosonde are compared, too. It is found that the combination of water vapor mixing ratio and GDAS temperature profiles allow us to derive relative humidity profiles with the relative uncertainty of 10-20 %.
ISSN: 1867-1381
DOI: 10.5194/amt-11-2735-2018
Rights: © Author(s) This work is distributed under the Creative Commons Attribution 4.0 License
Type: Article
Affiliation : Leibniz Institute for Tropospheric Research 
Ocean University of China 
Cyprus University of Technology 
Qingdao National Laboratory for Marine Science and Technology 
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