Accuracy of Raman lidar water vapor calibration and its applicability to long-term measurements

A Raman lidar calibration method adapted to the long-term monitoring of atmospheric water vapor is proposed. The accuracy of Raman lidar water vapor profiles is limited by that of the calibration process. Typically, calibration using in situ balloon-borne measurements suffers from the nonsimultaneity and noncollocation of the lidar and in situ measurements, while calibration from passive remote sensors suffers from the lower accuracy of the retrievals and incomplete sampling of the water vapor column observed by lidar. We propose a new hybrid calibration method using a combination of absolute calibration from radiosonde campaigns and routine-basis (off-campaign) partial calibration using a standard lamp. This new method takes advantage of the stability of traceable calibrated lamps as reliable sources of known spectral irradiance combined with the best available in situ measurements. An integrated approach is formulated, which can be used for the future long-term monitoring of water vapor by Raman lidars within the international Network for the Detection of Atmospheric Composition Change and other networks.