As of July 31, 2002, global multi-angle, multi-spectral radiance products are
available from the Multi-angle Imaging SpectroRadiometer (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 MISR 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.