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| Microwave Image | Visible Light Image |
These infrared, microwave, and visible images were created with data
retrieved by the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua
satellite.
Infrared Image
Because infrared radiation does not penetrate through clouds, AIRS infrared images
show either the temperature of the cloud tops or the surface of the Earth
in cloud-free regions. The lowest temperatures (in purple) are associated
with high, cold cloud tops that make up the top of the storm. In
cloud-free areas the AIRS instrument will receive the infrared radiation
from the surface of the Earth, resulting in the warmest temperatures
(orange/red).
Microwave Image
In the AIRS microwave imagery, deep blue areas in storms show where the
most precipitation occurs, or where ice crystals are present in the
convective cloud tops. Outside of these storm regions, deep blue areas may
also occur over the sea surface due to its low radiation emissivity. On
the other hand, land appears much warmer due to its high radiation
emissivity.
In the AIRS microwave imagery, deep blue areas in storms show where the
most precipitation occurs, or where ice crystals are present in the
convective cloud tops. Outside of these storm regions, deep blue areas may
also occur over the sea surface due to its low radiation emissivity. On
the other hand, land appears much warmer due to its high radiation
emissivity.
Microwave radiation from Earth's surface and lower atmosphere penetrates
most clouds to a greater or lesser extent depending upon their water
vapor, liquid water and ice content. Precipitation, and ice crystals found
at the cloud tops where strong convection is taking place, act as barriers
to microwave radiation. Because of this barrier effect, the AIRS microwave
sensor detects only the radiation arising at or above their location in
the atmospheric column. Where these barriers are not present, the
microwave sensor detects radiation arising throughout the air column and
down to the surface. Liquid surfaces (oceans, lakes and rivers) have "low
emissivity" (the signal isn't as strong) and their radiation brightness
temperature is therefore low. Thus the ocean also appears "low
temperature" in the AIRS microwave images and is assigned the color blue.
Therefore deep blue areas in storms show where the most precipitation
occurs, or where ice crystals are present in the convective cloud tops.
Outside of these storm regions, deep blue areas may also occur over the
sea surface due to its low radiation emissivity. Land appears much warmer
due to its high radiation emissivity.
Vis/NIR Image
The AIRS instrument suite contains a sensor that captures radiation in four bands
of the visible/near-infrared portion of the electromagetic spectrum. Data
from three of these bands are combined to create "visible" images similar
to a snapshot taken with your camera.
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.
