New maps of land surface temperature and snow cover produced by NASA’s
Terra satellite show this year’s winter was warmer than last year’s,
and the snow line stayed farther north than normal. The observations
confirm earlier National Oceanic and Atmospheric Administration reports
that the United States was unusually warm and dry this past winter.

For the last two years, a new sensor aboard Terra has been collecting
the most detailed global measurements ever made of our world’s land
surface temperatures and snow cover. The Moderate-resolution Imaging
Spectroradiometer (MODIS) is already giving scientists new insights
into our changing planet.

MODIS data reveal that average winter temperatures in clear-sky
conditions during the 2001-02 winter in the contiguous United States
were more than 3 C (5.4 F) warmer in the daytime and more than 2 C
(3.6 F) warmer at night than the winter of 2000-01.

Daytime temperatures in December 2001 were 4.6 C (8.3 F) warmer than
December 2000. January and February 2002 were also warmer than in
2001, and unseasonable warmth extended back into the fall, with
November temperatures almost 6 C (10.8 F) warmer in 2001 than 2000.
Some of the biggest temperature differences occurred in the northern
Great Plains, which were much warmer than last year, and northern
Utah, which was colder.

Zhengming Wan, a remote-sensing scientist at University of California,
Santa Barbara, developed the new technique for using MODIS data to
determine the surface temperature of the Earth. According to Wan,
“The land surface temperature maps from MODIS provide independent
evidence of previous reports that this past winter was warmer than
normal and confirm our ability to observe from space a characteristic
of the Earth that is important for studying global change.”

His team’s initial evaluation of the MODIS land surface temperature
observations found that most of MODIS’ space-based temperature
measurements agreed with comparable ground-based measurements to
within 1 C (1.8 F). Results will be published in a special issue of
the journal Remote Sensing of Environment later this year.

Unlike conventional observations of surface temperature that are
actually measurements of air temperature collected by thermometers
2 meters (6.6 feet) above the ground, MODIS measures precisely the
thermal radiation emitted from the planet’s surface — whether that
surface is bare ground, lakes, treetops, or rooftops. This additional
detail means farmers could know the temperature of the air around
their crops and the temperature of the crops themselves, which helps
farmers better estimate productivity and water requirements.

MODIS measures the temperature of nearly every square kilometer
(0.4 square miles) of the Earth’s surface roughly twice a day. This
regular coverage enables MODIS to observe snow cover, as well.
Monthly MODIS maps showing snow-covered areas from November 2001 to
February 2002 reveal that along with high temperatures, snow was
late to arrive and early to recede in many parts of the United States.

November’s snowline remained well north of its average location near
the border of the United States and Canada, and large areas of the
U.S. Rocky Mountains saw little persistent snow cover that month.
In February, at least 16 states from the Rocky Mountains eastward
showed little to none of their expected snow cover.

Many parts of the U.S. depend on snowmelt for recharging public
water supplies. MODIS’ observations of the extent of snow cover
allow scientists to more accurately estimate water availability in
the spring and summer months.

Launched December 18, 1999, NASA’s Terra satellite is the flagship
of the Earth Observing System series of satellites, part of NASA’s
Earth Science Enterprise, a long-term research program dedicated
to understanding how human-induced and natural changes affect our
global environment. Terra MODIS observations are expected to
continue through at least 2004.

More information, including images and animations, can be found at: