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

Abstract

Abstract. We compare aerosol optical thickness (AOT) and precipitable water vapor (PWV) 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 Flight Center scanning Raman lidar system, which operated from Wallops Island, Virginia (37.86øN, 75.51 øW), are compared with those measured by the Lidar Atmospheric Sensing Experiment (LASE) airborne lidar system aboard the NASA ER-2 aircraft. Bias and root-mean-square differences indicate that these measurements generally agreed within about 10%. Aerosol extinction profiles and estimates of AOT are derived from both lidar measurements using a value for the aerosol extinction/ backscattering ratio Sa = 60 sr for the aerosol extinction/backscattering ratio, which was determined from the Raman lidar measurements. The lidar measurements of AOT are found to be generally within 25% of the AOT measured by the NASA Ames Airborne Tracking Sun Photometer (AATS-6). However, during certain periods the lidar and Sun photometer measurements of AOT differed significantly, possibly because of variations in the aerosol physical characteristics (e.g., size, composition) which affect Sa. 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 lidars show that aerosols were generally concentrated in the lowest 2-3 km.

Characteristics of aerosols over Hyderabad in southern Peninsular India: synergy in the classification techniques

“…This R f value is larger than those found in winter and postmonsoon, suggesting water uptake and increase in size of the water-soluble urban aerosols due to humidification processes (see Gobbi et al, 2007) as the RH over Hyderabad is usually above 75 %. Such aerosol particles are composed of a large fraction of nitrates and sulfates, which are strongly hygroscopic in nature (Ferrare et al, 2000). The increasing AOD results in a shift towards zero dα and lower η values.…”

LASE Measurements of Water Vapor, Aerosol, and Cloud Distributions in Saharan Air Layers and Tropical Disturbances

“…Aerosol scattering ratios were derived from the off-line wavelength that was positioned at about -35 pm away from the strongly absorbing H 2 O line at 817.223 nm. Corrections for absorption by water vapor, air, and aerosol extinction) were applied to retrieve the aerosol scattering profiles [7]. The layer extended from near the surface to about 6 km in altitude.…”

“…In order to derive these profiles, the ratio of aerosol extinction/backscatter ("lidar ratio") was derived directly from the LASE data. LASE measurements both above and below an elevated dust layer were used to derive an estimate of transmission through the layer from which a value of the lidar ratio = 36 sr was obtained [7,8]. Also shown in Figure 3a are the extinction profiles at three wavelengths derived from the DC-8 in situ nephelometer measurements of aerosol scattering and PSAP measurements of absorption when the DC-8 descended through the dust layer.…”

Tropospheric water vapour and relative humidity profiles from lidar and microwave radiometry

“…It plays a key role in the global radiation budget and in energy transport mechanisms in the atmosphere (Whiteman et al, 1992;Ferrare et al, 2000) as well as in photochemical processes (Haefele et al, 2008). Moreover, it is the most important gaseous source of infrared opacity in the atmosphere, accounting for about 60 % of the natural greenhouse effect for clear skies (Kiehl and Trenberth, 1997), providing the largest positive feedback in model projections of climate change (Held and Soden, 2000).…”