Aerosol Animation

Aerosol Optical Depth (AOD) defines the degree to which aerosols prevent the transmission of sunlight by absorption or scattering.  AOD is measured using an integrated extinction coefficient over a vertical column of air.  The extinction coefficient can be used to analyze solar extinction and the performance of solar power systems as a function of location and time.


The animation maps aerosol optical depth for the GCC countries using average daily values for the month of April.  April is a key month for seasonal transition and the emergence of the Shamal winds.  The animation presents AOD for the 550nm wavelength, which is the portion of the sunlight spectrum most visible to the human eye and central to the performance of photovoltaic power systems.

The data behind the animation is NASA Earth science data generated using the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model.  GOCART simulates the behavior of major tropospheric aerosol components, including sulfate, dust, black carbon, organic carbon, and sea-salt aerosols.  GOCART provides extinction coefficients for each.  The animation is indicative of sunlight attenuation from dust only.

AOD data can be downloaded here.  The data is sourced in the binary netCDF format using FTP servers or using manual processing with the Giovanni online data system.  Giovanni  is maintained by the Goddard Earth Science Data and Information Service Center (GES DISC).

The code below analyzes AOD dust data in R.  The code opens the netCDF files sourced from NASA and converts the data into spatial data frames.  A uniform coordinate reference system is applied to facilitate integration with other spatial data for layered map creation.  The code also employs thin plate splines from the fields package in R to downscale the daily data from low resolution (2.5 by 2.5 degrees) to high resolution (100 meters by a 100 meters).  Unlike other interpolation methods, thin plate splines do not distort the original data, or propagate errors across the map domain, since interpolation is strictly limited to discrete areas (e.g. convex hulls).  The animation is created using a loop that walks through the daily data to create a layered map for each day, which is then saved as a *.png file.  The last line of code calls the open-source package ImageMagick to convert the daily files to a *.gif animation. 


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