Figure 1: click on image for larger AIRS microwave image
At 1:30 a.m. local time this morning, the remnants of (now Tropical Depression)
Katrina were centered on the Mississippi-Tennessee border. This microwave
image from the Atmospheric Infrared Sounder instrument on NASA's Aqua
spacecrat shows that the area of most intense precipitation was concentrated
to the north of the center of activity.
The infrared image shows how the storms look through an AIRS Infrared
window channel. Window channels measure the temperature of the cloud tops
or the surface of the Earth in cloud-free regions. The lowest temperatures
are associated with high, cold cloud tops that make up the top of the
hurricane. The infrared signal does not penetrate through clouds, so the
purple color indicates the cool cloud tops of the storm. In cloud-free
areas, the infrared signal is retrieved at the Earth's surface, revealing
warmer temperatures. Cooler areas are pushing to purple and warmer areas
are pushing to red.
The microwave image (figure 1) reveals where the heaviest precipitation
in the hurricane is taking place. The blue areas within the storm show
the location of this heavy precipitation. Blue areas outside of the storm
where there are moderate or no clouds are where the cold (in the microwave
sense) sea surface shines through.
The Atmospheric Infrared Sounder Experiment, with its visible, infrared,
and microwave detectors, provides a three-dimensional look at Earth's
weather. Working in tandem, the three instruments can make simultaneous
observations all the way down to the Earth's surface, even in the presence
of heavy clouds. With more than 2,000 channels sensing different regions
of the atmosphere, the system creates a global, 3-D map of atmospheric
temperature and humidity and provides information on clouds, greenhouse
gases, and many other atmospheric phenomena. The AIRS Infrared Sounder
Experiment flies onboard NASA's Aqua spacecraft and is managed by NASA's
Jet Propulsion Laboratory, Pasadena, Calif., under contract to NASA. JPL
is a division of the California Institute of Technology in Pasadena.