Aerosol Monitoring Using a Scanning Spectral Radiometer in Sendai, Japan

Abstract

Measurements of direct solar irradiance and sky radiance were carried out in Sendai, Japan for the period from September 1981 to May 1985 using a scanning spectral radiometer (aureolemeter). Size distributions of columnar total aerosols were retrieved by inverting both spectral optical thickness and solar aureole radiance data.The size distribution of aerosols due to the El Chichon eruption in 1982 was estimated as the difference between columnar volume spectra before and after the eruption. The results indicate that the El Chichon aerosol had a monomodal volume spectrum with a mode radius about 0.5 ,*m; their contribution to the total aerosol volume reached the maximum in the winter of 1983, i. e. December 1982 to February 1983, then gradually decaying to the normal level prior to the eruption by the spring of 1985.A seasonal model of tropospheric aerosols over Sendai was constructed by subtracting the volume spectrum of the El Chichon aerosol model from that of the columnar total aerosols, and successfully represented by a bimodal log-normal function. The aerosols in spring and summer seasons have different features in respect of volume spectra. The coarse particle mode aerosols with radii around 3 *m are predominant in spring while the accumulation mode aerosols with radii around 0.2µm are predominant in summer.

The MODIS 2.1-μm channel-correlation with visible reflectance for use in remote sensing of aerosol

“…Spectra taken of semi-arid vegetation suggest the possibility that this method may be extended to vegetated surfaces with . Remote sensing of aerosol over the land from the MODIS sensor, planned to be launch as part of the Earth Observing System in 1998, will be based on detection of dark targets using mid-IR channels (e.g., 2.1 and 3.9 m- [32]) and aerosol models that vary with the atmospheric conditions and are based on aerosol climatology derived from observations of the whole atmospheric column [12], [17], [25], [35]. This work is a first step in applying the 2.1-m channel for this purpose.…”

“…They are, though, very important in measuring the aerosol physical and optical properties [8], [17], [24], [35]. Recently there has been a resurgence of interest in aerosol radiative forcing of climate by direct reflection of sunlight to space [2], [20], [26] and by their effect on cloud microphysics and albedo [3], [11], [18], [22], [37].…”

Size distribution and scattering phase function of aerosol particles retrieved from sky brightness measurements

“…Study of the optical and physical properties of aerosol particles is important for assessment of their effect on climate [Charlson et al, 1991[Charlson et al, , 1992 high accuracy for particle radius in the range 0.1 -< r -< 8/am [Nakajima et al, 1983[Nakajima et al, , 1986aShiobara et al, 1991]. The effect of multiple scattering is also smaller in the forward direction than in the backward direction.…”

“…The retrieval of information from sky radiance at la•ge scattering angles requires accurate correction for the effects of multiple scattering and for the contribution of light reflected from the Earth's surface and scattered downward in the atmosphere. Recently, Nakajima et al [1983, 1986b] developed and applied [Nakajima et al, 1986a[Nakajima et al, , 1989Shiobara et al, 1991] an inversion scheme that includes accurate radiative transfer modeling to account for multiple scattering.…”

Influence of aerosols and thin cirrus clouds on the GOSAT-observed CO&lt;sub&gt;2&lt;/sub&gt;: a case study over Tsukuba

“…The sky radiometer can measure aerosol optical thickness and single scattering albedo at four wavelengths (400, 500, 675, and 870 nm), and the Angstrom exponent can be estimated from the optical thickness at these four wavelengths (Shiobara et al, 1991;Kobayashi et al, 2006). A large value of the Angstrom exponent indicates small particles.…”