As of July 31, 2002, global multi-angle, multi-spectral radiance
products are available from the MISR instrument aboard the Terra satellite.
Measuring the radiative properties of different types of surfaces, clouds
and atmospheric particulates is an important step toward understanding the
Earth's climate system. These images are among the first planet-wide
summary views to be publicly released from the Multi-angle Imaging
SpectroRadiometer experiment. Data for these images were collected during
the month of March 2002, and each pixel represents monthly-averaged
daylight radiances from an area measuring 1/2 degree in latitude
by 1/2 degree in longitude.
The top panel is from MISR's nadir (vertical-viewing) camera and combines
data from the red, green and blue spectral bands to create a natural color
image. The central view combines near-infrared, red, and green spectral data
to create a false-color rendition that enhances highly vegetated terrain.
It takes 9 days for MISR to view the entire globe, and only areas within
8 degrees of latitude of the north and south poles are not observed due
to the Terra orbit inclination. Because a single pole-to-pole swath
of MISR data is just 400 kilometers wide, multiple swaths must be mosaicked
to create these global views. Discontinuities appear in some cloud patterns
as a consequence of changes in cloud cover from one day to another.
The lower panel is a composite in which red, green, and blue radiances
from MISR's 70-degree forward-viewing camera are displayed in the northern
hemisphere, and radiances from the 70-degree backward-viewing camera are
displayed in the southern hemisphere. At the March equinox (spring in the
northern hemisphere, autumn in the southern hemisphere), the Sun is near
the equator. Therefore, both oblique angles are observing the Earth in
"forward scattering", particularly at high latitudes. Forward scattering
occurs when you (or MISR) observe an object with the Sun at a point in
the sky that is in front of you. Relative to the nadir view, this geometry
accentuates the appearance of polar clouds, and can even reveal clouds
that are invisible in the nadir direction. In relatively clear ocean areas,
the oblique-angle composite is generally brighter than its nadir counterpart
due to enhanced reflection of light by atmospheric particulates.
MISR data are processed at the Atmospheric Sciences Data Center at NASA's
Langley Research Center in Hampton, VA. These sample images were generated
from MISR's newly-released Global Georectified Radiance Product.
Image credit: NASA/GSFC/LaRC/JPL, MISR Team.
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