This NASA image combines sea surface temperature (SST) data obtained by
the Aqua program, cloud data from the GOES satellite, and land data from
the Terra satellite to show the atmospheric and oceanic conditions during
Hurricane Katrina in 2005. All three pieces of the image use the
principles of passive remote sensing, detecting radiation emitted by the
earth at certain wavelengths. The Aqua program used the Advanced Microwave
Scanning Radiometer for EOS (AMSR-E) instrument to detect the SSTs. This
is a passive-microwave radiometer, so it detects radiation in the
microwave region of the spectrum (>100 microns). SSTs can also be measured
using infrared wavelengths (~10 microns) but then it is more likely to be
affected by the presence of clouds. The clouds in the image come from
visible imagery, so it detects radiation in the visible region of the
spectrum (~0.5 microns). The land image was obtained using the MODIS
instrument, which also detects radiation in the visible region of the
spectrum.