Aerosol optical thickness

They are provided on the NEO web site as 1-day measurements and 8-day and 1-month composites. There are many applications for aerosol optical thickness data: " 1 Atmospheric correction of remotely sensed surface features 2 Monitoring of sources and sinks of aerosols 3 Monitoring of aerosol optical thickness eruptions and forest fire 4 Radiative Transfer Model 5 Air Quality 6 Health and Environment 7 Earth Radiation Budget 8 Climate Change" 1 "Aerosol particles are important to scientists because they represent an area of great uncertainty in their efforts to understand Earth's climate system, aerosol optical thickness. Depending upon their size, type, and location, aerosols can either cool the surface, or warm it. They can help clouds to form, or they can inhibit cloud formation.

Tiny solid and liquid particles suspended in the atmosphere are called aerosols. Windblown dust, sea salts, volcanic ash, smoke from wildfires, and pollution from factories are all examples of aerosols. Depending upon their size, type, and location, aerosols can either cool the surface, or warm it. They can help clouds to form, or they can inhibit cloud formation. And if inhaled, some aerosols can be harmful to people's health. Satellite measurements of aerosols, called aerosol optical thickness, are based on the fact that the particles change the way the atmosphere reflects and absorbs visible and infrared light.

Aerosol optical thickness

This post contains formulas! Aerosols play a great role in the atmospheric effects. Aerosols are particles suspended in the atmosphere, which can be of several types: sand or dust, soot from combustion, sulfates or sea salt, surrounded by water… Their size ranges between 0. Their quantity is also extremely variable : rain can suddenly reduce their abundance known as « aerosol optical thickness ». The abundance variations result in great variations of observable reflectances from one day to the next, and it is therefore necessary to know the quantity and type of aerosols, in order to correct their effects. Unfortunately, to correct the effects of aerosols, there is no global aerosol observation network, and the only available data are local observations from the few hundred points of Aeronet network. Therefore, this network can not be used operationally to correct the satellite images over large areas. Weather forecast models just start predicting the amounts of aerosols , based on satellite observations and modeling of sources and sinks and of the transport of aerosols by the winds, but these data do not seem to have sufficient accuracy yet to be used for the atmospheric correction of images. Our atmospheric correction method, named MACCS, is therefore based on an estimate of aerosol optical depth from the images themselves. To understand how this method works, one must already understand the effects of aerosols on radiation. We have seen in this post, that the effects of diffusion can be modelled as follows assuming the corrected gas absorption :. We seek to know the surface reflectance, but for each measurement made at the top of the atmosphere, there are three unknowns to be determined. To separate the effects of the atmosphere and surface effects, we must use other information. We can therefore deduce the atmospheric reflectance and using a radiative transfer model, the aerosols optical thickness AOT. However, this method assumes that there is a very dark area in the image which is not always the case , and that the reflectance of the dark surface is known.

This method works well in temperate and boreal zones, but not in arid areas where it is difficult to find the dense vegetation. Environmental Science and Pollution Research Indeed, aerosol optical thickness, the reflectance depend on the viewing angles: this is what we call directional effects.

In physics , optical depth or optical thickness is the natural logarithm of the ratio of incident to transmitted radiant power through a material. Thus, the larger the optical depth, the smaller the amount of transmitted radiant power through the material. Spectral optical depth or spectral optical thickness is the natural logarithm of the ratio of incident to transmitted spectral radiant power through a material. The use of the term "optical density" for optical depth is discouraged. In chemistry , a closely related quantity called " absorbance " or "decadic absorbance" is used instead of optical depth: the common logarithm of the ratio of incident to transmitted radiant power through a material, that is the optical depth divided by ln Optical depth measures the attenuation of the transmitted radiant power in a material. Attenuation can be caused by absorption, but also reflection, scattering, and other physical processes.

An aerosol optical depth product has been recently added. Aerosol optical depth is a measure of the extinction of the solar beam by dust and haze. In other words, particles in the atmosphere dust, smoke, pollution can block sunlight by absorbing or by scattering light. AOD tells us how much direct sunlight is prevented from reaching the ground by these aerosol particles. It is a dimensionless number that is related to the amount of aerosol in the vertical column of atmosphere over the observation location.

Aerosol optical thickness

In the maps shown here, dark brown pixels show high aerosol concentrations, while tan pixels show lower concentrations, and light yellow areas show little or no aerosols. Black shows where the sensor could not make its measurement. Aerosol optical depth is the degree to which aerosols prevent the transmission of light by absorption or scattering of light. Tiny solid and liquid particles suspended in the atmosphere are called aerosols. Examples of aerosols include windblown dust, sea salts, volcanic ash, smoke from fires, and pollution from factories.

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But due to the impact of surface albedo, geography and relief as well as retrieval algorithms, the precision of data reception requires continuous improvement 28 , 29 , 30 , Y and W. Figure 1. Comparison of coincident Multiangle Imaging Spectroradiometer and Moderate Resolution Imaging Spectroradiometer aerosol optical depths over land and ocean scenes containing Aerosol Robotic Network sites. Spring dust events and local soil dust emission contribute to increase of aerosol concentration. Optical depth is calculated based on spectral attenuation of ray at each wave length with Beer-Lambert-Bouguer Law, which is based on measurement of direct solar radiation with the aim of subsequent determination of atmospheric AOD and total content of certain gases. Satellite measurements of aerosols, called aerosol optical thickness, are based on the fact that the particles change the way the atmosphere reflects and absorbs visible and infrared light. Depending upon their size, type, and location, aerosols can either cool the surface, or warm it. IEEE Geosci. Fiore, A. I: Methodology and composition of flora and fauna.

Tiny solid and liquid particles suspended in the atmosphere are called aerosols. Windblown dust, sea salts, volcanic ash, smoke from wildfires, and pollution from factories are all examples of aerosols.

Figure 7. In order to better understand the accuracy and reliability of the data obtained, the decision was taken to carry out cross check of MODIS and MISR products as well as their efficiency with ground based aerosol measurement data, being a reference standard for determination the efficiency of aerosols retrieval algorithm based on satellites, obtained from ground based photometric observations of AERONET. Remote Sens. Shanghai statistical yearbook. Generally, the results obtained at the four stations show similar regression trends with R 2 values ranging from 0. The multi-spectral method works best on sites covered with vegetation and is much less accurate on arid sites, while the multi-temporal method performs a little worse on green sites, but much better on dry sites. They can help clouds to form, or they can inhibit cloud formation. Luo, Y. You, W. Pahlevan et al.