|
PUBLISHER'S Perspective
Field of Dreams
The winds of change are stirring, there could
be storm clouds on the horizon—something’s brewing in the geospatial
world! Who would have wagered, a year or so ago, heck, even
six months ago, that DigitalGlobe would win NIMA’s $500 million
NextView contract over Space Imaging, and that the latter’s
former CEO, John Copple, would become the head of Sanborn, one
of the major mapping and photogrammetry firms in America. This
is an auspicious example of how the intermarriage between
remote sensing and photogrammetry is converging the two worlds.
It is the twin towers of photogrammetry and satellite remote
sensing that constitutes the commercial remote sensing industry.
However, there is another area of remote sensing that most often
does not get our attention, and although it is not considered
commercial, its value to society far outweighs the costs.
The thought that comes to mind when thinking of weather satellites
is, “taken for granted.” There is a lot of technology that many
of us “take for granted” on a daily basis, such as: the picture
on the television, the satellites that transmit the picture
and, in the case of weather, the satellites that take the pictures
and transmit them all over the world. “Taken for granted” is
how weather satellites must have been perceived when, in a recent
appropriations committee meeting, a congressional staffer asked,
“Why do we need to spend so much money on weather satellites
when we can get all our weather information off the Internet?”
A recent visit to ITT Industries’ Aerospace/Communication Division
facility outside Fort Wayne, Indiana provided the fascinating
insight that the technology which allows us to see a weather
event such as Hurricane Isabel played out, moment by moment
on TV or the Internet, has roots that go back six decades and
are buried deep below an Indiana cornfield—all the way down
to the bedrock in fact.
In 1939, Dr. Philo Farnsworth, father of electronic television
and named one of the brightest minds of the last century by
Time and Newsweek, brought a cadre of engineers and investors
to Fort Wayne, Indiana to help advance his work on television
and radio broadcasting. His breakthrough Image Dissector tube
was the first commercially viable system for producing and transmitting
an electronic image. His work was also widely known in government
circles, at that time, where there were growing requirements
for remote imaging from high altitude air and space crafts.
The Aerospace/Communication Division of ITT Industries
got its start in 1949 when ITT purchased the Farnsworth
Corporation of Fort Wayne, Indiana. In 1967, the first geostationary
space sensor system for meteorology was launched on board the
ATS-3. In 1968 the first low earth space sensor for meteorology
was launched on board NIMBUS. Both the ATS and NIMBUS carried
ITT Imagers with tubes developed by Dr. Farnsworth.
Currently, GOES and POES constitute two-thirds of the National
Weather Service’s national warning system for severe weather.
The other third is made up of the ground-based NEXRAD radars.
The two GOES satellites, GOES West and GOES East, provide half-hourly
observations of the central and eastern Pacific, Hawaii,
and the Gulf of Alaska, North, Central, and South America, and
the central and western Atlantic. Each satellite carries two
major instruments: an Imager and a Sounder providing high resolution
visible and infrared data, as well as temperature and moisture
profiles of the atmosphere.
GOES is most famous for its hurricane images. GOES provides
forecasters images of local weather trouble spots, allows them
to improve short-term forecasts for local areas, and provides
multiple measurements of weather phenomena through a sounding
instrument that allows forecasters to increase their accuracy
of forecasts. GOES is able to detect and track thunderstorms,
flash floods, winter snow and ice storms, and important ocean
events such as hurricanes.
GOES also provides the instantaneous relay functions for the
SARSAT system. A dedicated search and rescue transponder
on board GOES is designed to detect emergency distress signal
origination from downed aircraft or ships in distress.
Complementing the geostationary satellites are the polar-orbiting
satellites (POES). These satellites support long-range forecasts
using two primary instruments: the Advanced Very High Resolution
Radiometer (an Imager) and the High Resolution Infrared Radiation
Sounder. The polar satellites track global variables in the
atmosphere and oceans that affect weather and climate. This
includes visible and infrared data for temperature profiling,
sea surface temperatures, and vegetation index and moisture
soundings. They also provide measurements for long-term global
climate change and ozone depletion.
Together GOES and POES help maintain a comprehensive understanding
of current and future weather to protect the nation and its
economic infrastructure from severe weather, extreme events,
and unusual climate. They also contribute to preserving marine
and coastal habitats, navigation safety, and search and
rescue. These and follow-on systems use devices developed by
ITT, but they are all based on the pioneering work of Philo
Farnsworth.
In partnership with DOD, NASA, and NOAA—a new polar satellite
program, the National Polar-orbiting Operational Environmental
Satellite System (NPOESS) will be available in 2008. NPOESS
merges the Military DMSP satellite with POES and creates a whole
new set of technologies to increase long-range forecasts. It
is predicted that the merging of these two systems will save
the taxpayers $1.8 billion over the life of the program.
One of the primary sensors within the NPOESS system is the Crosstrack
Infrared Sounder (CrIS), which will collect upwelling infrared
spectra at very high spectral resolution, and with excellent
radiometric precision. This data, when merged with microwave
data from other sensors on the NPOESS platform, is used to construct
highly accurate temperature, moisture, and pressure profiles
of the earth’s atmosphere.
To understand the importance of CrIS for metrological uses,
we need to compare it to the existing technology, the HIRS sounder,
which flies on the NOAA polar-orbiting metrological satellites
and provides thermal infrared measurements in 12 spectral
bands. The next-generation Crosstrack Infrared Sounder (CrIS),
currently under development by ITT at Fort Wayne, provides measurements
of the thermal radiation in 712 spectral bands. The differences
are critical performance drivers for the weather modeling and
forecasting done at the National Weather Service. In particular,
the improved accuracy at higher altitudes is important as the
upper atmospheric layers are believed to be long-term drivers
of much of the weather effects at lower levels. The bottom line
is the greater number of spectral bands, and increased resolution
and accuracy of the CrIS allows better modeling of the atmosphere
by the National Weather Service—which translates to more accurate
storm forecasting.
Ultimately, the performance of the CrIS, which incorporates
an interferometer, is directly related to how parallel two mirrors—the
dynamic alignment mirror and the porch swing mirror—can
be kept. And, how well the difference in effective optical path
lengths between these two optical paths is known. Both of these
objectives are affected by anything that causes unintended motion
of either mirror. Therefore, it is critical to control vibration
disturbances of the instrument. For laboratory tests, vibration
is controlled through both mounting and environmental controls.
The instrument is rigidly mounted to an isolation table,
a large 3' x 4' x 2' granite slab which resists “wiggling.”
This table is then isolated from the laboratory floor by isolation
legs directly tied to the underlying bedrock, because even the
slightest vibration from a passing car on the street outside
could affect results.
While touring the ITT facility outside Fort Wayne, Indiana,
one can’t help feeling awed—not so much by the monolithic,
non-descript, black, plate-glass building sitting in the middle
of a cornfield in what looks like rural Indiana. Rather, when
one considers the infinite minutiae of scientific detail and
the monumental engineering feats that are involved in developing
the technology and capability to build, launch, operate,
and disseminate the information derived from weather satellites,
one realizes it is anything but trivial and the benefits to
society are innumerable.
So the next time we watch the weather on TV or on the internet,
we may take for granted the technology involved—we may take
for granted the lives, money, assets, and infrastructure that
are saved—but, it’s a good bet we’ll remember that both the
television and remote sensing technology that allow us to watch
a storm unfold, across the country or across the county, were
made possible more than 60 years ago by a guy named Philo Farnsworth
in a cornfield in Indiana.
Until next time . . . Cheers!
Roland Mangold
Back
|
