Strong synoptic winds usually help to disperse pollutants over the skies
of Greece and the Aegean Sea during winter months, and in late summer
relatively strong northly winds typically prevent significant aerosol
influx from the south. During the summer of 2002, the northly Etesian
winds were exceptionally weak, allowing Sahara dust from the south to
reach the Aegean region. This resulted in elevated aerosol levels,
particularly in the month of July. The abundance of aerosol over Greece
and the Aegean Sea on four dates during the summer of 2002 are
illustrated by these images from the Multi-angle Imaging
SpectroRadiometer (MISR).
In the natural-color images (the left-hand panel of each pair), it is
apparent that aerosol particles are more abundant over the region on the
two dates in July than in either June or August. These natural-color
views were acquired by MISR's 70-degree forward-viewing camera. The top
and bottom views depict overlapping parts of mainland Greece and the
Aegean, with the bottom panels covering a region to the west of the top
panels. Data from each of the four dates have been processed
identically, and relative brightness variations between the views are
preserved.
MISR retrieves information on aerosol amount and particle properties by
using the changes in scene brightness and contrast at nine widely-spaced
view angles and four spectral bands. The right-hand panel of each image
pair is a map of retrieved aerosol amount, parameterized by a quantity
called aerosol optical depth. A color scale is used to represent this
quantity. Higher amounts of aerosol within the total column of the
atmosphere are indicated by green, yellow or orange pixels, and clearer
skies are indicated by purple and blue pixels. Dark gray pixels indicate
places where clouds or other factors precluded an aerosol retrieval.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earth
continuously from pole to pole, and every 9 days views the entire globe
between 82 degrees north and 82 degrees south latitude. This data
product was generated from a portion of the imagery acquired during
Terra orbits 13325, 13558, 13660 and 14126. The panels utilize data from
blocks 59 to 62 within World Reference System-2 paths 182 and 183.
MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.
Image credit: NASA/GSFC/LaRC/JPL, MISR Team
Text acknowledgment: Clare Averill (Acro Service Corporation/Jet Propulsion Laboratory).
Scientific interpretation acknowledgment:
Maria Kanakidou and Nikos Mihalopoulos, Department of Chemistry,
University of Crete, Heraklion, Greece.
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