Abstract
Monitoring of near-surface aerosol is important for both public health issues and radiation budget studies. In this study, we report a continuous observation method of aerosol particles by means of a vertical Mie-scattering lidar in combination with other optical and sampling instruments operated at the ground level. In the Fernald method used for processing the lidar signal, the most appropriate value of lidar ratio at 532 nm is estimated from the Mie-scattering calculation. The input parameters, namely, the mode radius, variance, and both real and imaginary parts of refractive index, are so determined as to reproduce the data from ground-based sampling instruments. Instead of the far-end boundary condition, the extinction coefficient at the surface level is used for constraining the retrieved aerosol extinction profile. The correction of the truncation and relative humidity (RH) effects on the scattering data from the sampling is made with the help of the optical data from a visibility-meter. We discuss the observed features in both low and high RH cases. Such a capability will be useful for uninterrupted lidar observations of near-surface aerosols irrespective of the presence of clouds that often hinders signal observations at higher altitudes where the aerosol-free atmosphere is assumed for the conventional Fernald analysis.
Highlights
The effects of atmospheric aerosols have been discussed in the context of both public health and the Earth’s radiation budget in relation to global climate change [1]
The problem in the conventional analysis based on the Fernald method [2] is that first, the value of lidar ratio (S1) has to be assumed, and second, lidar signals at the far-end boundary is needed so that the analysis can be started at the nearly aerosol-free altitude, 5~6 km above the surface
The value of lidar ratio can be estimated by means of the Mie-scattering calculation using aerosol parameters of the mode radius, variance, and the real and imaginary parts of refractive index
Summary
The effects of atmospheric aerosols have been discussed in the context of both public health and the Earth’s radiation budget in relation to global climate change [1]. Mie-scattering lidars have provided a valuable tool for studying aerosol profiles as well as the aerosol-cloud interaction. In the lower troposphere, the high variability of aerosol property leads to the substantial change in the lidar ratio. The presence of lower clouds often makes it impossible to observe lidar signals at higher altitudes. These problems can potentially be solved by combining the lidar data with sampling and optical data from instruments continuously operated in the observatory where the lidar setup is installed [3], [4]. The Mie-scattering calculation is implemented to reproduce the observed aerosol properties at the surface level, and this provides us with the value of S1 as well
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