During Spring 2003, students, teachers, and scientists worked side-by-side, measuring the properties of aerosols
(fine particulate matter suspended in the air) over Baltimore, Maryland using hand-held instruments. The
campaign had two objectives: providing NASA with high-quality, ground-based measurements to check aerosol
properties derived from satellite observations, and helping students learn about possible health effects of aerosols in the region. Health effects are of special interest, since school children in the Baltimore metropolitan area suffer from one of the highest asthma rates in the United States.
These four image panels from the Multi-angle Imaging SpectroRadiometer (MISR) instrument, which flies on
NASA's Terra satellite, were acquired on May 20, 2003, when the sky was about 50% covered by high, thin,
cirrus clouds. The two panels along the top are natural-color images from MISR's directly downward-viewing
(nadir) camera (left) and 60º forward-viewing camera (right). Cloudy weather predominated this spring, and of the
entire three-month campaign, May 20th was the least-cloudy day during which MISR flew over the study region.
Cirrus clouds are more apparent at the steeper viewing angle, and appear to shift position relative to the surface
between the two camera views due to the effect of geometric parallax. At lower left is a stereo height field
derived using the parallax effect. It shows that most of the cirrus clouds are about 10 kilometers above the
surface. At lower right is a map of satellite-retrieved aerosol amount (optical depth). These MISR products have
different scales. MISR's highest-resolution imagery is acquired at 275 meter pixel resolution, about the same size
of a major league baseball stadium, whereas the aerosol retrievals are produced at 17.6 kilometers, about the size
of a small city. To derive aerosol amount, the MISR retrieval algorithm examines the variation in scene brightness
over nine view angles and four spectral bands. Under cloudy conditions, it is especially challenging to measure
aerosol properties, and MISR makes use of special multi-angle cloud-screening techniques.
The AERONET global network of autonomous, ground-based, aerosol measuring instruments plays a key role in testing satellite aerosol retrievals. For the May 20 Baltimore experiment, scientists set up an additional eight AERONET instruments at schools and in parts of the Washington Metropolitan area to supplement the standard AERONET stations. Students at 12 schools also used hand-held sun photometers to measure aerosol amount as Terra, and several other satellites flew overhead. The campaign team will combine the single-point measurements made at these ground stations with the regional aerosol picture obtained from the satellites, to create a clearer view of Baltimore's aerosol characteristics. They will then compare the derived aerosol distribution with survey data on health effects, such as the incidence of asthma, to complete their study.
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. These data products were
generated from a portion of the imagery acquired during Terra orbit 18193. The panels cover an area of about 246
kilometers x 292 kilometers, and utilize data from blocks 59 to 60 within World Reference System-2 path 15.
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), Ralph Kahn (Jet
Propulsion Laboratory).
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