Comparison of aerosol optical properties and water vapor among ground and airborne lidars and Sun photometers during TARFOX

We compare aerosol optical thickness (AOT) and precipitable water vapor (PW V) measurements derived from ground and airborne lidars and Sun photometers during the Tropospheric Aerosol Radiative Forcing Observational Experiment . Such comparisons are important to verify the consistency between various remote sensing measurements before employing them in any assessment of the impact of aerosols on the global radiation balance. Total scattering ratio and extinction profiles measured by the ground-based NASA Goddard Space Fli ght Center scanning Raman Iidar system, which operated from Wallops Island, Virginia (37.86 degrees N, 75.51 degrees W), are compared with those measu red by the Lidar Atmospheric Sensing Experiment (LASE) airborne lidar syste m aboard the NASA ER-2 aircraft. Bias and root-mean-square differences indi cate that these measurements generally agreed within about 10%. Aerosol ext inction profiles and estimates of AOT are derived from both lidar measureme nts using a value for the aerosol extinction/ backscattering ratio S-a = 60 sr for the aerosol extinction/backscattering ratio, which was determined f rom the Raman lidar measurements. The lidar measurements of AOT are found t o be generally within 25% of the AOT measured by the NASA Ames Airborne Tra cking Sun Photometer (AATS-6). However, during certain periods the lidar an d Sun photometer measurements of AOT differed significantly, possibly becau se of variations in the aerosol physical characteristics (e.g., size, compo sition) which affect S-a. Estimates of PWV, derived from water vapor mixing ratio profiles measured by LASE, are within 5-10% of PWV derived from the airborne Sun photometer. Aerosol extinction profiles measured by both lidar s show that aerosols were generally concentrated in the lowest 2-3 km.