Aerosol optical depth and planetary albedo in the visible from the Solar Mesosphere Explorer

Abstract

The Solar Mesosphere Explorer (SME) satellite has observed the visible sunlight scattered at the earth's limb since early 1982. By using a radiative transfer model including multiple scattering and albedo effects, observations at 20°N latitude have been interpreted in terms of aerosol optical depth. The ratio of aerosol extinction to Rayleigh extinction at 431.8 nm shows a large increase after the eruption of El Chichon. A maximum ratio of 5 at 36 km and larger than 11 at 30 km occurs in the summer of 1982 followed by a decrease through 1983 and 1984. Aspects of the aerosol time evolution appear to be consistent with other observations and model predictions. Quantitative differences exist between inferred SME and lidar extinction coefficients, possibly due to the different wavelengths of the measurements and to the different scattering phase functions used in the two analyses. It is also shown that visible limb radiances provide information on the planetary albedo, which shows an increase from the equator to the poles with a maximum in the winter hemisphere and a minimum in the summer hemisphere.

Comparison of radiative transfer models for limb‐viewing scattered sunlight measurements

“…Measurements of scattered radiance in the limb of the atmosphere have been used for a variety of purposes: to detect stratospheric aerosol layers [ Cunnold et al , 1973; Naudet and Thomas , 1987; Elansky et al , 1991; McLinden et al , 1999], to measure stratospheric temperature [ Rusch et al , 1983], to measure mesospheric ozone concentration [ Rusch et al , 1984], to measure upper‐stratospheric NO 2 concentration [ Mount et al , 1984], and to determine sensor attitude [ Janz et al , 1996; Hilsenrath et al , 1997; Sioris and Chance , 2003; Kaiser et al , 2003]. As scientific interest in the ozone concentration in the troposphere and lower stratosphere has intensified, the limb scattering technique has been proposed as a possible source of profile information [ Malchow and Whitney , 1977; Aruga and Heath , 1982; Flittner et al , 2000; Auvinen et al , 2002; Strong et al , 2002; McDade et al , 2002; Kaiser et al , 2002].…”

LIMBTRAN: A pseudo three‐dimensional radiative transfer model for the limb‐viewing imager OSIRIS on the ODIN satellite

“…Few, if any, other pseudo 3-D limb models fully account for this. They include the models of Naudet and Thomas [1987] and Abreu et al [1989] who also use a somewhat different approach to approximate for multiple scattering than employed here. The publicly available RT code MODTRAN [Berk et al, 1989] uses an approach similar to that used here to calculate limb radiances.…”

Description and sensitivity analysis of a limb scattering ozone retrieval algorithm

“…The first step in the algorithm is to produce an estimate of the surface reflectivity using the measured radiance at large tangent heights, as described by Naudet and Thomas [1987]. Although the THN procedure described in section 2.1.1 greatly reduces the sensitivity of the retrieved ozone to the surface reflectivity R , a surface reflectivity estimate is needed in the MS correction step.…”

“…If reliable aerosol information is available (from a LS aerosol retrieval algorithm such as Naudet and Thomas [1987] or from some other source), then this information can be introduced into the ozone retrieval algorithm by using the aerosol information to construct the model atmosphere for the inversion's forward calculations (IFC) and the look‐up table. Exactly correct aerosol information (size distribution as well as profile) eliminates the ozone retrieval error in the background aerosol case.…”

“…Measurements of scattered radiance in the limb of the atmosphere have been used to determine a variety of atmospheric properties, including stratospheric aerosol [ Cunnold et al , 1973; Naudet and Thomas , 1987; McLinden et al , 1999], stratospheric temperature [ Rusch et al , 1983], mesospheric ozone concentration [ Rusch et al , 1984], upper‐stratospheric NO 2 concentration [ Mount et al , 1984], and sensor attitude [ Janz et al , 1996; Hilsenrath et al , 1997; Sioris et al , 2001; Kaiser et al , 2004]. The limb scatter (LS) technique has been proposed as a possible source of ozone profile information in the upper troposphere and lower stratosphere.…”