PUBLIC INFORMATION OFFICE

JET PROPULSION LABORATORY

CALIFORNIA INSTITUTE OF TECHNOLOGY

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

PASADENA, CALIFORNIA 91109.

TELEPHONE (818) 354-5011



PHOTO  CAPTION                                            P-43887

                                                   April 13, 1994

                                                                

This picture is a three-dimensional perspective view of Death

Valley, California.  This view was constructed by overlaying a

SIR-C radar image on a U.S. Geological Survey digital elevation

map.  The SIR-C image is centered at 36.629 degrees north

latitude and 117.069 degrees west longitude.  We are looking at

Stove Pipe Wells, which is the bright rectangle located in the

center of the picture frame.  Our vantage point is located atop a

large alluvial fan centered at the mouth of Cottonwood Canyon. 

In the foreground on the left, we can see the sand dunes near

Stove Pipe Wells.  In the background on the left, the Valley

floor gradually falls in elevation toward Badwater, the lowest

spot in the United States.  In the background on the right we can

see Tucki Mountain.  This SIR-C/X-SAR supersite is an area of

extensive field investigations and has been visited by both Space

Radar Lab astronaut crews. Elevations in the Valley range from 70

meters (230 feet) below sea level, the lowest in the United

States, to more than 3,300 meters (10,800 feet) above sea level.

Scientists are using SIR-C/X-SAR data from Death Valley to help

the answer a number of different questions about Earth's geology. 

One question concerns how alluvial fans are formed and change

through time under the influence of climatic changes and

earthquakes.  Alluvial fans are gravel deposits that wash down

from the mountains over time.  They are visible in the image as

circular, fan-shaped bright areas extending into the darker

valley floor from the mountains.  Information about the alluvial

fans helps scientists study Earth's ancient climate.  Scientists

know the fans are built up through climatic and tectonic

processes and they will use the SIR-C/X-SAR data to understand

the nature and rates of weathering processes on the fans, soil

formation and the transport of sand and dust by the wind.  SIR-

C/X-SAR's sensitivity to centimeter-scale (inch-scale) roughness

provides detailed maps of surface texture.  Such information can

be used to study the occurrence and movement of dust storms and

sand dunes.  The goal of these studies is to gain a better

understanding of the record of past climatic changes and the

effects of those changes on a sensitive environment.  This may

lead to a better ability to predict future response of the land

to different potential global climate-change scenarios.  Vertical

exaggeration is 1.87 times; exaggeration of relief is a common

tool scientists use to detect relationships between structure

(for example, faults and fractures) and topography.



Death Valley is also one of the primary calibration sites for

SIR-C/X-SAR.  In the lower right quadrant of the picture frame

two bright dots can be seen which form a line extending to Stove

Pipe Wells.  These dots are corner reflectors that have been set

up to calibrate the radar as the shuttle passes overhead.  Thirty

triangular-shaped reflectors (they look like aluminum pyramids)

have been deployed by the calibration team from JPL over a 40- by

40-kilometer (25- by 25-mile) area in and around Death Valley.  

The signatures of these reflectors were analyzed by JPL

scientists to calibrate the image used in this picture.  The

calibration team here also deployed transponders (electronic

reflectors) and receivers to measure the radar signals from SIR-

C/X-SAR on the ground.



-----



SIR-C/X-SAR radars illuminate Earth with microwaves allowing

detailed observations at any time, regardless of weather or

sunlight conditions.  SIR-C/X-SAR uses three microwave

wavelengths:  L-band (24 cm), C-band (6 cm) and X-band (3 cm). 

The multi-frequency data will be used by the international

scientific community to better understand the global environment

and how it is changing.  The SIR-C/X-SAR data, in conjunction

with aircraft and ground studies, will give scientists clearer

insights into those environmental changes which are caused by

nature and those changes which are induced by human activity.  

SIR-C was developed by NASA's Jet Propulsion Laboratory.  X-SAR

was developed by the Dornier and Alenia Spazio companies for the

German space agency, Deutsche Agentur fur 

Raumfahrtangelegenheiten (DARA), and the Italian space agency,

Agenzia Spaziale Italiana (ASI).



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