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Module 4 - Image Examples

B) Death Valley, California

Objectives

  1. Students will apply the skills they have learned in analyzing and interpreting radar image data to a data set from geology.

Look in the directory /Data/Mods1to5/Module04/Images/DeathVal/PreSIRC. You should find the following files in there:

An explanation of these images and their source follows.

Shuttlev.gif (337K GIF) - Hand-held photograph taken by a Space Shuttle crew member. The photograph is taken from an oblique angle, looking roughly Northwards. Death Valley is outlined in yellow. To the left of the image can be seen the southern end of the Sierra Nevada mountain range.

GroundV4.gif (106K GIF) - shows the Shuttle Hand-held photograph, plus photographs taken from the ground at four different locations within the scene. Site A is Mammoth mountain, a ski resort in the Eastern Sierras. Site B is located in the sand dunes found in the North end of Death Valley, Site C is a salt pan on the flat valley floor, and Site D is a rough salt deposit in the southern end of the valley. These images show the extremes of climate in California: in Mammoth (at around 9,000 feet above sea level) it is winter, and cold enough for deep snow to be on the ground; in Death Valley (at or below sea level) it is also winter, but warm enough to wear shorts and t-shirts.

LocatMap.gif (146K GIF) - digitized USGS map of part of Southern California, showing Death valley and its location with respect to Los Angeles. Los Angeles lies near the bottom left of the map, and Death Valley is near the top center. The distance from LA to Death Valley is around 300 miles, and it takes around 6 hours to drive there.

Landsat1.gif (202K GIF) - Landsat Thematic mapper image of Death Valley. The valley floor, which has salt deposits, appears yellow in this image. Death Valley is surrounded by mountains on both sides, and erosion of the rocks over time has formed alluvial fans, which consist of pieces of rock and sand. These alluvial fans can be seen in the Landsat image. Also shown on the image is a rectangular area, outlined in green. This area corresponds to the area to be seen in the AIRSAR radar images LBandful.gif, CBandRed.STK, LBandRed.STK, and PBandRed.STK.

GroundV2.gif (406K GIF) - ground photograph, showing the flat valley floor in the foreground (including a small bush), the alluvial fans in a strip across the center, and the mountains on the side of the valley in the background.

Topomap1.gif (430K GIF) - Digitized topographic map of part of Death Valley, showing heights above sea level in meters.

LBandFul.gif (1,370K GIF) - L-band HH radar image of the rectangular area outlined in green in Landsat1.gif (202K GIF). The area is known as Cottonball Basin. This image is rotated when compared with the Landsat1.gif image. It was collected by the NASA/JPL AIRSAR imaging radar system in May 1992. The radar was flying parallel to the top of the image and looking down and out to the left. At the top of the image can be seen an alluvial fan, with some mountains in the top right hand corner. In the center of the image are some salt flats, some of which are rough and appear bright in the radar image, some of which are smooth and appear dark in the radar image. About two-thirds of the way down, on the left-hand edge of the image, there is a ranger station, which is surrounded by trees and also has a small runway for aircraft.

VegmpByt.gif (41K GIF) - vegetation map of the CottonBall Basin area generated automatically from the AIRSAR data, using all three frequencies and all the different polarizations.

Looking at the vegetation map, you should be able to see the following:

  1. The valley floor is mostly classified as no vegetation (blue).
  2. The alluvial fan is mostly classified as low vegetation (light green), with some areas of no vegetation (blue).
  3. The ranger station is classified as forest (bright green and yellow).
  4. The are probably some incorrect classifications present - the medium vegetation (dark green) near the center of the image may be in error, and the low vegetation (D) classification near the top of the image is almost certainly an artifact.
  5. Several areas are unclassified (white, grey or black). This means that they do not match any of the models for vegetation type, etc. used in the classifier.

vegmpkey.gif (2K GIF) - key to the vegetation map shown in VegmpByt.gif (41K GIF). The color codes are:

VegmpHdr.txt - text file showing the percentage classification of each of the classes seen in the VegmpByt.gif file.

Notice, for example, that 36.2% of the image was classified as no vegetation, and 39.9% was classified as low vegetation.

CBandRed.STK - C-Band AIRSAR image data file containing all polarizations. To display, open the Sigma0 application by clicking twice on the icon, then select the Open Cmprsd Stokes option under the File menu. Select the VV polarization for display.

Now point to the lighter grey part of the alluvial fan with the mouse. The VV backscatter, seen in the bottom left hand corner of the image window, should be in the region of -5.0 dB, give or take a few dB. Pointing to the valley floor, the backscatter value will change to around -15.0 dB. Thus we can tell the difference between the alluvial fan and the valley floor by looking at the C-Band VV backscatter.

Next, draw a rectangle on the image within the alluvial fan by holding down the mouse while dragging, then release. Choose the Mean and Std Dev option under the Statistics menu and a set of numbers will appear in the Statistics window. The mean values corresponding to the selected rectangle under the Mean column should match closely the following numbers:

HH -7.2 dB
HV -12.8 dB
VV -5.0 dB
HHVV* phase 0.0 deg
Corr coefficient 0.45

These values correspond to the model for scattering from a vegetation layer, since the HV is almost 5.0 dB less than HH, the phase difference between HH and VV is close to 0 degrees, and the HH-VV correlation coefficient is reasonably close to one-third.

SiteText.txt - text file describing the Death Valley super site. The objectives of the investigators at the Death Valley site are included. Here is an excerpt, which contains a description of the site:

"DEATH VALLEY IS A N-S TRENDING FAULT-BOUNDED VALLEY IN THE SOUTHERN GREAT BASIN. ELEVATIONS RANGE FROM 70 M BELOW SEA LEVEL TO MORE THAN 3300 M ABOVE SEA LEVEL (TELESCOPE PEAK). CLIMATE AND VEGETATION VARY ACCORDINGLY, FROM SUBALPINE PINE FOREST AT HIGHER ELEVATIONS, TO ARID CREOSOTE ON THE PIEDMONTS, TO SPARSE SALT-TOLERANT PLANTS IN THE VALLEY BOTTOM. SURFICIAL PROCESS INVESTIGATIONS ARE CONCENTRATING MOSTLY ON THE PIEDMONT AND VALLEY FLOOR. THEY INCLUDE STUDIES OF THE FORMATION OF ALLUVIAL FANS THROUGH CLIMATIC AND TECTONIC EFFECTS, THE NATURE AND RATES OF WEATHERING PROCESSES ON THE FANS, SOIL FORMATION, AND THE TRANSPORT OF SAND AND DUST BY THE WIND. THESE ARE LONG-TERM STUDIES WITH THE GOAL OF BETTER UNDERSTANDING 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.

DEATH VALLEY IS A GOOD SITE FOR DEVELOPMENT AND TESTING OF TECHNIQUES FOR REMOTE LITHOLOGIC MAPPING BECAUSE OF THE WIDE RANGE OF ROCK TYPES EXPOSED IN A RANGE OF ENVIRONMENTS. THE PANAMINT MOUNTAINS, BOUNDING THE VALLEY ON THE WEST AND THE GRAPEVINE MOUNTAINS IN THE NORTH PART OF THE VALLEY, ARE COMPOSED OF A VARIETY OF IGNEOUS, METAMORPHIC, AND SEDIMENTARY ROCK TYPES. IN ADDITION, THERE ARE KNOWN AREAS OF ALTERATION THAT HAVE CREATED ECONOMIC DEPOSITS OF MINERALS.

AS PART OF THE SECONDARY OBJECTIVES, DEATH VALLEY HAS BEEN USED AS A TEST SITE FOR THE DEVELOPMENT OF RADAR INTERFEROMETRIC TECHNIQUES FOR MAPPING TERRAIN HEIGHTS. AT PRESENT, BOTH SEASAT AND TOPSAR DATA SETS ARE AVAILABLE AND ERS-1 INTERFEROMETER IMAGES WILL BE ACQUIRED IN 1993. IN ADDITION, A SPOT STEREO-PAIR HAS BEEN ACQUIRED AND IS BEING REDUCED TO DIGITAL TOPOGRAPHY FOR COMPARISON TO THE INTERFEROMETRIC DATA. THESE DATA ARE NOW BEING USED IN THE STUDIES DESCRIBED ABOVE. SOILS HAVE DEVELOPED IN DEATH VALLEY IN A WIDE RANGE OF SALINITY. THIS MAKES POSSIBLE STUDIES OF THE RADAR SIGNATURE OF SOILS THAT HAVE SUFFERED A BUILDUP OF SALT- A GROWING PROBLEM IN MARGINAL LANDS. FINALLY, AT THE NORTH END OF THE VALLEY LIES UBEHEBE CRATER, A SERIES OF VOLCANIC CRATERS (MAARS) CREATED BY EXPLOSION WITH VERY LITTLE ASSOCIATED LAVA. VOLCANOLOGISTS CAN STUDY THE RADAR SIGNATURES OF THE CRATERS AND EXPLOSIVE DEPOSITS."

Teacher's Guide - Table of Contents

Converted to the IBM-PC by Al Wong, sirced03@southport.jpl.nasa.gov

Jet Propulsion Laboratory
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