In order to achieve quantitative measurements of the Earth's surface radiance and reflectance, it is important to determine the aerosol optical thickness (AOT) to correct for the optical influence of atmospheric particles. An advanced method for aerosol detection and quantification is required, which is not strongly dependant on disturbing effects due to surface reflectance, gas absorption and Rayleigh scattering features. A short review of existing applicable methods to the APEX airborne imaging spectrometer (380nm to 2500nm), leads to the suggested aerosol retrieval method here in this paper. It will measure the distinct radiance change between two near-UV spectral bands (385nm & 412nm) due to aerosol induced scattering and absorption features. Atmospheric radiation transfer model calculations have been used to analyze the AOT retrieval capability and accuracy of APEX. The noise-equivalent differential AOT is presented along with the retrieval sensitivity to various input variables. It is shown, that the suggested method will be able to identify different aerosol model types and measure AOT and columnar size distribution. The proposed accurate AOT determination will lead to a unique opportunity of two-dimensional pixel-wise mapping of aerosol properties at a high spatial resolution. This will be helpful especially for regional climate studies, atmospheric pollution monitoring and for the improvement of aerosol dispersion models and the validation of aerosol algorithms on spaceborne sensors.
Massive smoke plume from forest fires reduced visibility on regional scale in Northeast Asia in May 2003 during boreal forest fire season in Siberia. Smoke aerosol events and their effects are investigated using satellite data from the Moderate Resolution Imaging Spectro-radiometer (MODIS), Measurement of Pollution in the Troposphere (MOPITT), Clouds and the Earth's Radiant Energy System (CERES), and Total Ozone Mapping Spectrometer (TOMS) over Northeast Asia. Extensive forest fires were detected from MODIS fire product (MOD14) data over Siberia. Aerosol optical thickness (AOT) of the smoke aerosol from fires can be retrieved from the MODIS Level 1 data by using the Bremen Aerosol Retrieval (BAER) algorithm. The retrieved mean AOT ranged from 2 to 4 over smoke plume covering Northeast Asia. Over most of the Northeast Asia, CO concentrations was about 3.0 molecules/cm2 in this region. The top-of-atmosphere (TOA) shortwave aerosol radiative forcing (SWARF) from CERES has been estimated. The mean TOA SWARF was about 130~290 W/m2 over smoke aerosol plume, indicating an aerosol cooling effect.
The paper is devoted to the application of the newly developed aerosol retrieval algorithm to a study of the aerosol optical thickness(AOT) spatial distributions for a number of hazard situations including fires and dust outbreaks. In particular we find that the spectral slope of the optical thickness decreases with the distance from a fire. This is owing to the aerosol aging mechanism. Also we discuss possible reasons for the spectral cloud optical thickness anomalous behaviour in the short-wave region.
This study is devoted to the development of a semi-analytical algorithm for the determination of the otpical thickness, the liquid water path and the effective size of droplets from spectral measurements of the intensity of solar light reflected from water clouds with large optical thickness. The algorithm is planned to be aplied to the data fromteh Scanning Imaging Absorption Spectrometer for Atmospheric Chartography, launched on March 1st, 2002 on board of the ENVIronmental SATellite. The probability of photon absorption by droplets in the visible and near-IR spectral regions is low. This allows us to simplify and modify well known asymptotic equations of the radiative transfer theory, taking into account the fact that the single scattering albedo is close to one. Modified asymptotic equations are used to develop the inverse algorithm. We also avoid the use of the Mie theory, applying parameterization and geometrical optics results with account for wave corrections. The main advantage of the method proposed lays in the fact that the equations derived not only provide a valuable alternative to the numerical radiative transfer solution. They are also much more simple than equations of a conventional asymptotic theory. This simplicity allows both the simplication of the cloud retrieval algorithm and, even more important, insight into various factors involved in cloud retrieval schemes.