Despite their delicate appearance, thin, feathery clouds of ice crystals called
cirrus may contribute to global warming. Some scientists believe cirrus is quite
common, but it is notoriously difficult to observe—even from satellites,
which offer our only means of monitoring such clouds over the entire planet.
The Multi-angle Imaging SpectroRadiometer (MISR), one of a new generation of
instruments flying aboard the NASA Earth Observing System’s Terra satellite,
views Earth with nine cameras simultaneously, some at very steep angles through
the atmosphere. Scientists on the MISR team have been hoping to learn what
contributions their instrument can make to a global inventory of cirrus. They
got their chance to test MISR’s capabilities during July 2002, when they joined
over 400 other scientists and six research aircraft at the US Naval Air Station
near Key West, Florida for the Cirrus Regional Study of Tropical Anvils
Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) field campaign. The
campaign had many goals, one of which was making simultaneous aircraft and
satellite measurements of cirrus.
On July 9, the ER-2 research plane, carrying a multi-spectral camera called the
MODIS Airborne Simulator (MAS), flew in the stratosphere above a
35-kilometer-wide patch of thin cirrus minutes after MISR imaged the cloud from
space. At the same time, another NASA high-altitude jet, the WB-57, flew right
through the 15-kilometer-high cloud with cloud particle counters and a particle
The left side of this montage is a natural-color view of the Caribbean Sea
east of the Yucatan Peninsula as seen by MISR’s most steeply forward-viewing
camera. The thin line running roughly north-south was drawn on this image along
the flight tracks of the stacked ER-2 and WB-57, and the red arrow points to a
crescent-shaped cirrus cloud. At right is a false-color image taken 700
kilometers closer to Earth by the MAS instrument on the ER-2. Data from the MAS shortwave
infrared channel that detects cirrus is shown in blue.
An animation of the cloud as seen by seven of the nine MISR cameras is also
available. It progresses from the most steeply forward to the most steeply backward
view, and excludes imagery from two angles which had significant sunglint. These
gray-scale images use MISR’s red band. The cirrus is prominent at the steeper
angles and virtually disappears in the nearly vertical views. Because it is so
much higher, the cirrus seems to move more than the background clouds. The
animation also shows the 3-dimensional structure of many towering cumulus
clouds. By analyzing these data sets, scientists will learn how effectively they
can use MISR observations to map thin cirrus, and to monitor changes in its
distribution from season to season and year to year. For more information about
the CRYSTAL-FACE campaign, visit: http://cloud1.arc.nasa.gov/crystalface/.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earth
continuously from pole to pole, and views almost the entire globe every 9 days.
This MISR image covers an area of about 232 kilometers x 267 kilometers.
Image courtesy NASA/GSFC/LaRC/JPL, MISR Team and the MAS Teams at NASA Goddard Space Flight Center and Ames Research Center.