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(Fwd) [clarc] Super-precise GPS




------- Forwarded message follows -------
Date sent:      	Thu, 21 Dec 2000 14:25:21 -0600 (CST)
From:           	Kyle Rhorer <rhorer@clarc.org>
To:             	Clear Lake Amateur Radio Club <clarc@clarc.org>
Subject:        	[clarc] Super-precise GPS
Send reply to:  	Kyle Rhorer <rhorer@clarc.org>

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov 

Contact: Rosemary Sullivant (818) 354-0474 

FOR IMMEDIATE RELEASE  December 15, 2000 

"WHERE AM I?" NASA'S BLACKJACK RECEIVER KNOWS THAT AND 
MORE 

       While an ordinary global positioning system (GPS) receiver uses
information carried by radio signals from a constellation of GPS
satellites to calculate its position, NASA's BlackJack GPS receiver looks 
at
the radio waves themselves. By making precise measurements of how the 
signals
are distorted or delayed along their way, the BlackJack provides a new 
way to
study Earth's gravity field and atmosphere.

       The first of these experimental receivers is flying on a German
scientific satellite, Challenging Minisatellite Payload (CHAMP), launched 
in
July. The second is onboard an Argentine satellite called SAC-C, 
launched on
November 21. Both instruments were designed and built at NASA's Jet
Propulsion Laboratory in Pasadena, Calif.

       "Like any other GPS receiver, the BlackJack can calculate where it is
in space and time, but comparing the BlackJack to an ordinary GPS 
receiver is
like comparing a home camcorder to a professional studio camera," said 
JPL
engineer Thomas Yunck, manager of the GPS Observatories Office. While 
a
typical GPS receiver can determine its position to about 20 meters (22
yards), the BlackJack can pinpoint the position of its host satellite
continuously with an accuracy of 2 to 3 centimeters (.8 to 1.1 inch). This
flight data can be used to improve computer models of the Earth's
gravitational field, which in turn can help reveal different Earth
properties, including the structure and evolution of the deep interior, the
movement of surface ice and atmospheric mass, and ocean circulation.

       In a more dramatic departure from conventional GPS use, BlackJack
receivers track the radio signals slicing through the earth's atmosphere as
the GPS satellites appear to rise and set. This information will help
scientists construct detailed images of the ionosphere and will provide
precise profiles of atmospheric density, pressure, temperature, and 
moisture
for climate studies and weather prediction. The BlackJacks are also 
equipped
with small down-looking antennas to attempt to receive GPS signals that
reflect off the oceans.  This highly experimental technique could one day 
be
used to map the subtle variations of the ocean topography, derive ocean
circulation patterns, sense the roughness or state of the ocean surface 
and
estimate surface winds.

       The SAC-C and CHAMP experiments are early attempts to assess the
engineering feasibility of such measurements. Both experiments are
designed to last about 3 years. 

       JPL is a division of the California Institute of Technology in
Pasadena. 


#####
12/13/00 RS
#2000-129 


-- 
         "The crux of the biscuit
                        Is the apostrophe"
                                      -Frank Zappa

                        Kyle Rhorer <rhorer@clarc.org>

------- End of forwarded message -------


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