Comparison of aerosol properties derived from sampling and near-horizontal lidar measurements using Mie scattering theory

Abstract

Aerosol optical properties are measured near the surface level using sampling instruments and a near-horizontal lidar. The values of the aerosol extinction coefficient inside the instruments are derived from nephelometer and aethalometer data, while the ambient values are measured from the lidar. The information on aerosol size distribution from optical particle counters is used to simulate extinction coefficients using the Mie scattering theory, with corrections on the humidity growth of hygroscopic particles. By applying this method to the continuous data obtained from November to December 2018 at Chiba, Japan, we elucidate the temporal variations of near-surface aerosol properties, including the complex refractive index, single scattering albedo, and Angstrom exponent. The results indicate how aerosol particles change their properties between the dry, instrumental conditions and relatively humid setting of the ambient atmosphere.

Continuous observations from horizontally pointing lidar, weather parameters, and PM2.5: a pre-deployment assessment for monitoring radioactive dust in Fukushima, Japan

“…These very close mean extinction coefficients can be attributed to the effect of relative humidity (RH), as discussed in the succeeding paragraph. The extinction coefficient values presented in this work are roughly ten times greater than previously reported works (Ong et al, 2019;Xiafukaiti et al, 2020). In these previous works, a laser inclined 4 • above the horizontal was used to observe near-horizontal aerosols.…”

“…The slope method is used by fitting a line between the maximum and minimum of the natural logarithm of the range-corrected signal between 100 m and 300 m. A homogeneous atmosphere can be assumed during the observation period in this horizontal range. This method is similar to our group's work that examined the relationship between horizontal lidar and weather effects from continuous lidar observations in November 2017 and in the winter of 2018 (Ong et al, 2019;Xiafukaiti et al, 2020). The depolarization ratio from the lidar signals is calculated as the ratio of the S and P signals multiplied by the ratio of the gains of the channels.…”

Multiwavelength LED lidar for near-ground aerosol distribution measurement

“…RC is defined as the maximum range of the region in which, to a good approximation, the logarithm of RCS linearly decreases with the range. This situation occurs typically for the present configuration of the near-horizontal lidar observation 8 . Under this condition, we can assume ∂(ln(X(R))/∂R ≈ -2αtotal from the lidar equation itself (here αtotal is range-independent).…”

“…Up to now, the LED lidar system only can measure the atmosphere at nighttime due to the wider divergence and low power of the LED light sources. Total (aerosols and molecules) extinction coefficients are derived from the lidar data following the method used in our previous work 8 . Briefly, we determine the spatial distribution of the total extinction coefficient, αtotal(RC), by solving the lidar equation using the Klett method 9 :…”

Exploration for adequate non-diffractive beam generation in dense scattering media

“…As an example, optical coherence tomography (OCT) is a non-invasive ophthalmologic diagnostic technique that renders an in-vivo cross-sectional view of the dense scattering media such as biomedical tissues up to a depth of less than 2 mm 7 – 9 . On the other hand, for long-range sensing, lidar is widely used for measuring optical properties of atmospheric particles and molecules that have smaller concentrations than biomedical tissues 10 .…”