Calibration Stability of the ARM Raman Lidar at ENA

Description

The Atmospheric Radiation Measurement (ARM) program currently operates Raman Lidars (RL) at the Southern Great Plains (SGP) site in Oklahoma, the Eastern North Atlantic (ENA) site in the Azores, and the third ARM mobile facility (AMF3) at Oliktok Point, Alaska. All three of these RLs share a similar hardware design and use the same data processing procedures. Recently we implemented a new algorithm, called the Feature detection and EXtinction (FEX). It uses several steps to estimate aerosol backscatter, scattering ratio, extinction, linear depolarization ratio, lidar ratio, and cloud and feature masks. The first step of this method is to estimate the overlap function and calibration constants. These calibration constants are used to calculate scattering and depolarization ratios which are key to estimating aerosol and cloud properties including extinction profiles. The calibration constants are site specific and depend on multiple parameters including the RL system constant, Rayleigh and Raman scattering cross-sections, nitrogen density profiles, and system misalignment angles. Changes in the calibration constants can provide valuable clues about system health and data quality. To better understand the quality of RL data at ENA, analyses of the temporal variability (2015 to present) of these constants will be presented.