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Learning
How to Explain the Rain INTRODUCTION:
Precipitation
is more complicated than water falling from the sky. Rain, snow, ice crystals,
clouds, and more all contribute to a complex process that circulates energy in
the atmosphere and helps regulate our planet’s climate. Recent efforts by
NASA and its partners have begun to reveal some of the subtleties that drive various
forms of precipitation around the world. But more research is needed. Now with
a new type of Earth based radar being utilized in actual field research tests,
the space agency is developing the technologies that will enable it to maximize
research systems of the future, already on the drawing board.
ECHOES
OF FALLING WATER
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Text
of Reporter Package: "What we don’t know about rain
far outweighs what we do know. That’s one of the reasons
NASA has developed the advanced N-Pol radar system. The facility
is the only one of its kind, utilizing an ultra-modern flat
panel radar antenna. It’s affiliated with the TRMM project,
a satellite based research mission that’s designed to
study rainfall in revolutionary ways.
John
Gerlach, NASA Scientist says, "To understand what the
satellite tells you you have to have some way of tying that
into the measurements on the ground, and that’s one of
the functions of the radar."
Located
on the shores of a sun-baked backwater in the Florida Keys, a research team from
NASA’s Wallops Island Flight Facility put the new radar system through its
paces. The system is portable and self contained …able to operate continuously
without re-supply for nearly two weeks.
Working in shifts 24 hours a day,
scientists and engineers monitored tropical rainfall in a roughly 250 mile radius.
They measured not only where and when rain fell, but also vital details about
its physical nature, like droplet size and concentration of atmospheric water
in a given area.
The team will fold their findings into ongoing research about
precipitation and global climate. Moreover, their experiments
here on a lonely spit of land are fundamental to the development
of the next generation precipitation monitoring system, currently
being developed for worldwide deployment in the latter part
of the decade."
NASA’S
NEW PORTABLE RADAR FACILITY
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It’s
called the N-Pol Radar system: NASA’s Polarimetric Radar. Capable of being
loaded entirely into four ordinary sea cargo shipping containers, this new, advanced
radar facility can be transported just about anywhere in the world with relative
ease. Engineers and scientists designed the system to make measurements about
distinct aspects of precipitation as it falls through the atmosphere. Characteristics
of interest include droplet size, quantity, duration of rainfall events, and more.
The rotating radar dish sees roughly 250 miles in any direction, rotating at a
variable rate and able to be tilted dynamically to facilitate a multi-layered
view of the atmosphere.
The facility utilizes a revolutionary flat panel
radar “dish” to transmit and receive its radar signals. Unlike more
traditional radar sites that use a parabolic bowl to send and receive radar signals,
this new systems uses carefully engraved dipoles that have been etched into a
specially prepared panel, much the same way that a circuit board in manufactured.
Each element is individually focused on the central feed horn—the small target
shaped object in front of the radar panel. The flat panel design has several significant
advantages over its more traditional cousin. First, it can be easily disassembled
for shipping; reassembly is equally easy. Second, the flat panel design allows
for dramatic weight reductions in the overall tower. Hundreds of symmetrical squares
of metal have been removed from the panel by precision laser cutting, thus decreasing
to total mass of the panel. These holes facilitate operation of the dish in unusually
windy environments by allowing air to pass right through the working structure
of the system. In addition, the wind-friendly architecture means that a radome—a
dome shaped structure designed to shield a turning radar dish—does not need
to be in place, also reducing overall weight. All together, this helps the overall
facility by reducing the needs for a massive mast to support the whole structure,
dramatically shrinking the total size of the facility and enhancing its ability
to be transported and set up quickly. At present, the N-Pol system run by the
team at NASA’s Wallops Island Flight Facility is the largest flat panel radar
in use anywhere in the world.
Powered by its own diesel generator, the facility
can operate in complete isolation for a period of up to two weeks, without re-supply
or other outside contact. The site maintains internet connectivity with a satellite
uplink, and cools its sensitive computer and radar equipment with self contained
air conditioning units. The facility only requires two people for full-scale operation
at any one time. CLOUDY
SKIES IN A WHOLE NEW LIGHT
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Radar
data collected by researchers at the facility can be displayed in ways that use
colors to designate specific characteristics. As it sweeps the sky in a circular
pattern, the radar antenna feeds its information into a sophisticated computer
program. The software essentially maps the sky in terms of precipitation, showing
a variety of details, from drop size to how much water exists at any one time
in a given volume of sky. In addition to its ability to color-code rainfall data,
the system can also store spatial information about what it sees, enabling researchers
to review and compare their data at a later time. A
MORE TANGIBLE MEASUREMENT OF RAIN
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In
addition to advanced radar installations and space age hardware on orbit, researchers
know that old data collections techniques are not necessarily out of date. Besides
measuring rainfall amounts by remote means, scientists have installed a series
of rain gauges throughout the Florida Keys. By measuring the actual rainfall amounts
collected over a discrete period of time, scientists can double check the readings
of their more contemporary data systems, in addition to provide a wider range
of geographic data to their archive.
In Image 2 we see a pair of rain gauges. They’re mounted
to a flat surface in a remote area of a mangrove swamp in
the Florida Keys. At the base of the tube, a protected electrical
port stays out of the rain, ready to be plugged into a laptop
computer. Like their analogous gauges scattered elsewhere,
these instruments can collect rainfall in a central container
and store it until technicians can come by to take readings.
TRMM: WATCHING RAIN FROM THE OTHER SIDE OF THE CLOUDS
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The
Tropical Rainfall Measuring Mission (TRMM) is the first Earth
Science mission dedicated to studying tropical and subtropical
rainfall, precipitation that falls within 35 degrees north
and 35 degrees south of the equator. Tropical rainfall comprises
more than two-thirds of the world’s total. The satellite
uses several instruments to detect rainfall including radar,
microwave imaging, and lightning sensors. Flying at a low
orbital altitude of 217 miles (350 kilometers), TRMM’s
study of tropical rainfall and attendant processes continues
to be a powerful scientific research tool. In fact, during
the past five years, this Japanese and American joint effort
has provided huge returns to the science community, from greater
understanding of how tropical rainfall affects overall climate,
to the energy budget surrounding global desert regions, to
revolutionary ways for studying hurricanes.
The Japanese space agency (NASDA) launched the satellite on an
H-II rocket from Tanegashima Space Center on November 27, 1997.
TRMM data
is available to researchers around the world. A team of scientists and engineers
at NASA’s Goddard Space Flight Center in Greenbelt, Maryland manages it.
Special
Thanks to Dr. John Gerlach, Observational Science Branch
The
Official Reproduction Guidelines
for Use of NASA Images and Emblems
This multimedia project is the work of a dedicated team of researchers, animators,
and media specialists. A detailed companion video to this web site is available
from NASA-TV. Below are a list of agencies, departments, and researchers who provided
expertise and data for this production: NASA
- Goddard Space Flight Center
Scientific Visualization Studio
Television
Production NASA-TV/GSFC
GSFC Studio 13 Content
Preparation & Project Production: Michael
Starobin
Mike McClare
GSFC
Public Affairs Contact: Wade Sisler
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