In late 1999, NASA launched the first in a series of new Earth
Observing Satellites (EOS) equipped with state-of-the art instruments
to observe the Earth as a system and monitor global
environmental changes over time. The EOS flagship spacecraft,
called
Terra flies in a polar
orbit, descending across the equator in the morning when cloud
cover
is at a minimum and its view of the surface is least obstructed.
This is because most of the Earth's land is in the northern hemisphere.
Later, in May of 2002, the Aqua spacecraft
was put into an ascending polar orbit timed to
cross
the equator in the afternoon and view the Earth's oceans when cloud
cover is usually at a minimum. In July of 2004, NASA launched
Aura to study the Earth's ozone,
air quality and climate. These three spacecrafts
kick off the Earth Observing Satellites series designed
to
measure
global
climate
change over first two decades of the 21st century.
Here are two images taken by a MODIS radiometer on the Terra
and Aqua satellites. It is striking to see that
the 2003 fall colors in Wisconsin change very quickly from green
to reds in just four days, probably due to a dry spell in July
and
August.
Aqua transmitted this image on October 6th,
2003 at 2pm |
Terra transmitted this
image on October 10th, 2003 at 10am |
Below are two more MODIS images that show the fall colors took
a little longer to change in 2004.
September 26th, 2004 |
October 9th, 2004
|
|