Mitigation of bias sources for atmospheric temperature and humidity in the mobile Weather & Aerosol Raman Lidar (WALI)

Abstract

7 Lidars using vibrational and rotational Raman scattering to continuously monitor both the water 8 vapor and temperature profiles in the low and middle troposphere offer enticing perspectives 9 for applications in weather prediction and studies of aerosol/cloud/water vapor interactions by 10 deriving simultaneously relative humidity and atmospheric optical properties. Several heavy 11 systems exist in European laboratories but only recently have they been downsized and 12 ruggedized for deployment in the field. In this paper, we describe in detail the technical choices 13 made during the design and calibration of the new Raman channels for the mobile Weather and 14 Aerosol Lidar (WALI), going over the important sources of bias and uncertainty on the water 15 vapor & temperature profiles stemming from the different optical elements of the instrument. 16 For the first time, the impacts of interference filters and non-common-path differences between 17 Raman channels, and their mitigation, are particularly investigated, using horizontal shots in a 18 homogenous atmosphere. For temperature, the magnitude of the highlighted biases can be much 19 larger than the targeted absolute accuracy of 1°C defined by the WMO. Measurement errors are 20 quantified using simulations and a number of radiosoundings launched close to the laboratory. 21