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246 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. G E ~ 2 4 , NO.2. MARCH 1986
Multipolarization Radar Images for Geologic
Mapping and Vegetation Discrimination
DIANE L. EVANS, TOM G. FARR,MEMBER, IEEE,
J. P. FORD,MEMBER, IEEE,
THOMAS W. THOMPSON, MEMBER, IEEE, AN D C. L. WERNER
Abstract-The NASAlJP L airborne synthetic aperture radar system
produces radar image data simultaneously in four linear polarizations
(HH, VV, VH, HV) at 24.6-cm wavelength (L-band), with 10-m reso
lution, across a swath width of approximately 10 km . Th e signal data
ar e recorded optically an d digitally an d annotated in each of th e chan
nels to facilitate a completely automated digital correlation. Both stan
dard amplitude, an d also phase difference images are produced in th e
correlation process. Individual polarization an d range-dependent gain
functions improve the effective dynamic range, bu t as yet do not per
mi t absolute quantitative measurements of the scattering coefficients.
However, comparison of the relative intensities of the different polar
izations in individual black-and-white and color composite images pro
vides discriminatory mapping information. In the Death Valley, Cali
fornia, area, rough surfaces of young alluvial deposits produce strong
responses at all polarizations_ Smoother surfaces of older alluvial de
posits show significantly lower responses. Evaporite deposits of differ
en t types an d moisture contents have distinct polarization signatures.
In the Wind River Basin, Wyoming, sedimentary rock units show po
larization responses that relate to differences in weathering. Local in
tensity variations in like-polarization images result from topographic
effects; strong cross-polarization responses denote the effects of vege
tation cover and, in some cases, possible scattering from the subsur
face. In the Savannah River Plant, South Carolina, forest cover char
acteristics ar e discriminated by polarization responses that reflect th e
density and structure of the canopy, and the presence or absence ofstanding water beneath the canopy. In each of th e areas studied, mul
tiple polarization data allowed discrimination and mapping of unique
characteristics of the surficial units.
I. INTRODUCTIONM ULTIPOLARIZED synthetic-aperture radar (SAR)
images were acquired over numerous geological,
agricultural, and forested targets by the NASAl Jet Pro
pulsion Laboratory (JPL) airborne radar in August and
September 1983 and again in March 1984. The data were
acquired at L-band (wavelength of 24.6 cm) simulta
neously in four polarization states: horizontal transmit,horizontal receive (HH); horizontal transmit, vertical re
ceive (HV); vertical transmit, vertical receive (VV); and
vertical transmit, horizontal receive (VH).
According to first-order theory for slightly rough sur
faces [1], like-polarized waves are most sensitive to the
Manuscript received June 14, 1984; revised July 10, 1985. The JP L
Aircraft Radar Program and the NASAIARC CV-990 Aircraft Programs
are supported by the NASA Office of Space Science an d Applications. This
work was performed in part by the JPL, California Institute of Technology,
under contract with NASA.
Th e authors are with the Jet Propulsion Laboratory, California Institute
of Technology, Pasadena, CA 91109.
IEEE Lo g Number 8407040.
-POLARIZED-- C R O S S ~ P O L A R I Z E D - - -VOLUME SCAffiR'lNG'-
1 I
o ]0 20 30 40 50 W 70 80 90
ANGLE OF INCIDENCE, (degrees)
Fig. 1. Relative contributions of different scattering processes to I i k e ~ and
c r o s s ~ p o l a r i z e d backscatter. Note that the relative c r o s s ~ p o l a r i z e d level,
normally much lower than like polarized, has been increased for clarity
(from [3]).
spatial frequency corresponding to the Bragg resonant
condition. Fo r rougher surfaces, higher order theories
predict a mixture of surface and subsurface scattering
contributions [2]. Fig. I schematically shows the relative
contributions of surface and subsurface volume scattering
as shown in the Manual of Remote Sensing [3].
Cross-polarized returns result only from second-order
effects involving surface multiple scatter and subsurface
volume scatter. Most theories predict domination of cross
polarized returns by subsurface volume scattering [2], [4].
For rough surfaces with high dielectric constants, how
ever, surface multiple scattering may contribute signifi
cantly to the return. Fo r low-loss targets such as dry al
luvium, the contribution from the subsurface probably
dominates the cross-polarized return, and bulk properties
such as number of rocks per cubic meter, porosity, andmoisture content become the important target character
istics. Vegetation canopies are also strong volume scatterers, and commonly exhibit a high cross-polarized com
ponent. Work is continuing on the evaluation of theories
that predict the multipolarization radar backscatter re
sponse of natural targets. As calibrated data become more
commonly available, quantitative determinations of ter
rain characteristics may be possible. At the present time,
however, we are restricted to qualitative statements as in
dicated above.
Preliminary analysis of multiple polarization radar data
shows that they are extremely useful for mapping surficial
0196-2892/86/0300-0246$01.00 © 1986 IEEE
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EVANS et al.: RADAR IMAGES FOR MAPPING AND DISCRIMINATION 247
1 - - - - - - - -A IRC-RA-FTI
I EQUIPMENT IDESK-TOP €il-
'
CV-990 COMPUTER RADARNAVIGATION - - - - - - - - - - - - -+__e - ____________________ ,
, INFO LOGS
II,
III,
I
I
FORMATTER,!
AIDCONVERTER
RADAR
ELECTRONICS
L _ _ _ _ _
DIGITAL
TAPE
RECORDER
I + - - " " " " " " ~ V A X DIGITALCORRELATOR
I OSTFLIGHT
DATA PRODUCTIONL- __
USER
_ __ --.J
Fig. 2. JPL aircraft SAR system overview. Aircraft operations acquire rawdigital tapes and exposed signal film, which are processed to produce
SAR images sometime after the aircraft flights.
TABLE I
JPL L-BAND RADAR PARAMETERS
Parameter ValuE'
Radar freq uency
Wavelength
Pulse length
Bandwidth
Peak power
Antenna azimuth beamwidth
A n t e n n ~ range beamwidth
Antenna beam center gain
Nominal al t i tude
Nominal veloci ty
Nominal pulse repet i t ion frequency
Number of l ooks
Dynamic range
Azimuth ambigui t ie s
Receiver noise f igure
1215 MHz
24.6 em
4. 9 )lS
19.3 MHz
4 kW
12 dB
6. 0 to 12.0 kID
zoo to 250 m/ s
60 0 to 800 pps (Dual po l . )
1200 to 1600 pp s (Quad pol . )
2 op t i ca l
4 d ig i t a l
12 dB op t i ca l
22 dB d ig i t a l
-2 0 dB op t i ca l
-3 0 dB d ig i t a l
8 dB
deposits, mapping sedimentary rocks, and mapping a for
est canopy.
II. DATA ACQUISITION
The NASA/JPL L-band aircraft SAR is described by
Thompson [5]. A block diagram for the radar is shown in
Fig. 2, and a list of the radar operating parameters is pre
sented in Table I. The radar is normally installed on the
NASAlAmes Research Center (ARC) CV -990 researchaircraft. Most of the radar electronics, including dual re
ceivers and the traveling wave tube transmitter, are 10-
cated in the CV -990 aft baggage compartment. Dual an
tennas, one horizontally polarized and the other vertically
polarized, are mounted on a baggage door on the aircraft's
starboard side. The antennas have an 18° beamwidth
along-track (i.e., parallel to the aircraft's velocity vector)
and 75 0 beamwidth in a plane perpendicular to the air
craft's velocity. Radar echoes from ground targets are re
ceived by the antenna, amplified, and heterodyned tovideo frequencies. These video signals are recorded on
both optical and digital recorders. In order to facilitate the
processing, the radar pulse repetition frequency (prO is
varied with aircraft ground speed, which is derived from
the aircraf t's inertial navigation system. A desk-top com
puter located in the passenger compartment of the CV-
990 aircraft is used to control the radar operation.
In-flight operations produce two forms of raw data-an
optical recorder film and a high-density digital tape
(HOOT). Following the flights, optical survey images are
produced using optical correlator techniques such as those
described by Kozma et al. [6]. Digital data are recordedin-flight by digitally sampling the heterodyned video sig
nal at a sample rate of 40 MHz.
The JPL SAR has the capability of simultaneously col
lecting linear like-polarized (HH and VV) and cross
polarized (HV and VH) backscatter data. The transmitter
alternately drives the horizontally and vertically polarized
antennas while dual receivers simultaneously record the
like-polarized and cross-polarized echo signals. In this
manner, all possible combinations of linear polarization
are recorded. The polarizations, which are interleaved on
the high-density digital tape (HOOT), are decoded by the
computer during the correlation process. The resultingmultiple polarization images are perfectly registered. Since
the four polarization channels are recorded essentially
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248 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. GE-24, NO.2, MARCH 1986
simultaneously, phase differences between the differently
polarized returns also can be formed into images. Work
is being pursued on the utility of images depicting the
phase difference between the VV and HH channels,
Data acquired in different polarization modes have dif
ferent swath widths. In the quad polarization mode, the
optical and digital coverage is 50 to 60fJ-S
in range, whichrepresents ground coverage from nadir to approximately
10 km to the right of the aircraft ground track. In the dual
polarization mode, the range coverage is doubled. In this
mode, transmitted pulses are either vertically or horizon
tally polarized and both polarizations are recorded. Thus,
the data are either HH and HV or VV and VH. Typical
flight altitudes are 6 to 12 km. The resulting far-range
angles of incidence are near 45 a and 63 0 for the "quad
pol" and "dual pol" images, respectively. Typical re
cording times are a few minutes, yielding up to several
kilometers of along-track coverage.
III. DIGITAL DATA PROCESSING
Digital data acquired by the JPL SAR are annotated with
the aircraft altitude, attitude and position, date and time
of day, transmitter power, receiver gains, and polariza
tion mode. This annotation makes it possible to com
pletely automate the correlation process. The processing
is performed on a VAX 111780 with a FPS AP-120B array
processor and takes approximately 5 h per four-polariza
tion image set.
A. Imaging Algorithm
A synthetic aperture radar return can be modeled as thetwo-dimensional convolution of the projected scene back
scatter and point target response [7]. The projection is
onto a curved plane defined by the direction the sensor is
travelling and the range vector pointing from the radar to
the imaged point (Fig. 3). The convolving functions are
the transmitted waveform expressed in spatial coordi
nates, and the two-dimensional azimuthal chirp [8].
The transmitted waveform for the JPL SAR is a linear
FM chirp signal with a bandwidth of 19.3 MHz. Match
filtering of the radar return with the azimuthal chirp cor
relates the image in the range dimension and determines
the range impulse response. The transmitter waveform hasbeen weighted with a Hamming window to reduce the
range sidelobe level, with a commensurate reduction inrange resolution. The unwindowed range resolution is
given by
c2')' = 7.9 m
where c is the speed of light and')' is the chirp rate.
Azimuth correlation of the range-compressed data re
quires matched-filtering of the phase history of each pixel
as recorded by the sensor as it travels along the flight path.
For spaceborne SAR data, azimuth correlation is a twodimensional filtering operation, to account for range mi
gration [9], [10]. For aircraft SAR, however, the effective
Fig. 3. Aircraft SAR imaging geometry. The aircraft moves with velocityV along X and images a(x, r) at incidence angle e.
SLANT
RANGE SAMPLI NG----j
INTERVAL I
r(xll
Fig. 4. Curve of equal range in the (x, r) plane demonstrating range cur-vature.
azimuth window can be made narrow enough, either
physically or by digital filtering of the raw data, so that
the range migration remains within a slant range sampling
interval (Fig. 4).Azimuthal resolution is determined by the length of the
synthetic aperture and the distance the sensor travels while
a target is within the effective azimuth antenna pattern.
The azimuth resolution ( \) is given by
r(O) " r(O) "b = -- = -- = 10.98 mx 2L 2N&
where reO) is the perpendicular range to the scatterer, " is
the radar wavelength, L the synthetic aperture length, &
the azimuth sampling interval, and N is the number of
samples in the azimuth reference function. The small size
of the JPL L-band antenna requires that the azimuth sampling interval be small. Rather than processing the ac
quired data to full resolution, the data are decimated in
azimuth by a digital bandpass filter so that the correlated
image resolution is similar in range and azimuth. Speckle
noise in the SAR image is reduced through summation of
high-resolution images ("looks") obtained by bandpass
filtering of the complex-valued correlator output.
B. Data Format
Digital image parameters are summarized in Table II.
Output from the correlation process is in two forms: real
valued data files, which preserve the full dynamic rangeof the image; or 8-bit pixel format. The 8-bit images have
a linear scaling applied so that the average magnitude is
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EVANS et al.: RADAR IMAGES FOR MAPPING AND DISCRIMINATION
TABLE II
RADAR IMAGE PARAMETERS
Parameter Value
Azimuth pixel spacing 11 meters
Azimuth resolution 13 meters
Number of looks
Slant range pixel spacing 7.5 meters
Slant range resolut ion 7. 9 meters
Ground range pixel spacing, @1O deg. 43 meters
@30 deg. 15 meters
@50 deg. 9.8 meters
Look angle range 0-57 deg. Quad pol .
0-68 deg. Dual pol.
0-75 deg. Single pol .
set to the middle of the display dynamic range. The blackand-white images presented in the following section rep
resent the standard output product from the JPL digitalcorrelator. They have had only a Gaussian contrast stretchapplied before the images were printed. Since the multiplepolarization images are automatically registered, imagesacquired in each of three polarization states can be encoded as the red, green, and blue planes of color composite images. In this way, differences in the polarization
response of different targets can be viewed simultaneously.
There are several constraints to consider when comparing image intensities from different polarizations and incidence angles. Individual polarization and range-dependent gain functions have been applied to the receivers toimprove their effective dynamic range. The correlator doesnot compensate for these gain variations at present. Thegain functions have been chosen such that surfaces of
equal roughness have similar brightness for most incidence angles across the swath. Other systematic errors,including range and azimuth antenna patterns, have not
yet been removed from the data. However, the gain variations do not change rapidly, especially for incidence an
gles greater than 300
• In this regime, itis
valid to makerelative comparisons of intensities for different polariza
tions and incidence angles. Although absolute quantitative measurements of scattering coefficients are not avail
able as yet, the multipolarization data have been shownto be extremely useful in the analyses described below.In addition to color composite images, "polarization signatures" of some units have been extracted from the digital data based on mean DN values in extended regions.
IV . GEOLOGIC MAPPING AND VEGETATION
DISCRIMINATION
A. Mapping Suificial Deposits
Radar images can furnish valuable data for the mapping
of surficial deposits of differing age, lithology, and chem-
249
ical compOSItIon. Surfaces such as alluvial fans, pediments, and playas are common in desert areas and containinformation related to the geologic conditions in the pres
ent and recent past.Death Valley, in eastern California, has been used as a
test site for remote-sensing technique development for anumber of years because of the well-exposed examples of
common geologic surfaces. Multipolarized radar images
were obtained August 30, 1983, over the central part of
Death Valley. HH, VV, VH images, and a color composite of the three polarizations are shown in Fig. 5(a)
(d), respectively. "Polarization signatures" were extracted for several units in the scene by finding the mean
DN of an extended area within each unit. These signaturesare displayed in Fig. 6. The area of the images is char
acterized by a variety of Quaternary alluvial gravels, evaporite deposits and Tertiary alluvial, lacustrine, and volcanic deposits (Fig. 5(e)). Furnace Creek fan centered at
C3, is the most prominent feature in the images. The
bright point-returns at the apex of the fan are from Furnace Creek Inn and the square feature at B3 is the resortcomplex of Furnace Creek Ranch. The active part of the
fan consists of its upper half at C3, above the dark band.
This part of the fan consists of gravels washed down byFurnace Creek. The dark band represents the point atwhich the particles on the fan become too small, less than
about one-tenth the radar wavelength, to scatter the L-
band radar waves back to the sensor [11]. Below the darkband (A3, B4-D4, E3), Furnace Creek fan is composed
of flood plain deposits and carbonate evaporites. Mesquite trees preferentially occupy drainages on the flood
plain deposits as shown in Fig. 7. Along with the vegetation at the Ranch, these trees are the only significantvegetation in the scene. Their relatively strong responsein the cross-polarized channel (Fig. 5(c)) is a result of
multiple scattering from the leaves and the limbs of thetrees. This is expressed as a blue to purple color in theseareas in Fig. 5(d), but also can be seen in curve a of Fig.6, which illustrates the relative polarization response of
vegetation on Furnace Creek fan.To the south of Furnace Creek fan, at F-G2, are several
smaller fans made up of young gravels. These have thesame dark band at their bases, but are darker overall than
the Furnace Creek fan. This is because their streams aredraining areas of less resistant rock types that weather topebbles less than 2 cm in size. To the right of these fans,at H3, is an outcrop of the Pliocene Funeral fanglomerate
[12]. This ancient alluvial deposit contains volcanic boul
ders up to 1 m in diameter. The outcrop has a distinctbright pink signature in the color composite indicatingstrong returns at all polarizations, with a slightly higherrelative return at HH. Fig. 6 shows the polarization signature of the Funeral fanglomerate graphically. The relatively high cross-polarized return may be the result of
multiple scattering among the closely packed boulders.
These results indicate that multipolarization radar imagesmay be used to discriminate rock types by their erosionalcharacteristics in an alluvial fan environment.
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0
(a)
(c)
IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. GE-24, NO.2, MARCH 1986
~ k m
(e)
EXPLANATION
DROUGH ANDfROOEOSAlT
D MOOTH SALT
OCARBONATE ZONE ISALINE FACIES
OCARBONATE ZONE
SAND FACIES
• FLOODPLAIN DEPOSITS
[J YOUNG FAN GRAVELS
m'i INTERMEDIATELill FAN GRAVELS
§ OLD FAN GRAVELS
I§ FUNERALf§ I FANGLOMERATE
UNDIVIDED
PRE PLEISTOCENE ROCKS
(b)
~ k m (A i lUtlll')
(d)
5. Multipolarization images of Death Valley, CA, centered on 36°20'N, 116°50'W. Images acquired August 30, 1983. (a) Like polarization (HH).
(b) Like polarization (VV). (c) Cross polarization (VH). (d) Color composite (HH = red, VV = green, VH = blue). (e) Geologic map of Furnace
Creek area of Death Valley simplified from Hunt and Mabey [12) . Also shown are locations of field photographs (Figs. 7-9).
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EVANS el at.: RADAR IMAGES FOR MAPPING AND DISCRIMINATION
220
LHH"RED LVH -BLUE LVV -GREEN
Fig. 6. Polarization signatures composed of mean DN values for rectangular areas of units in Death Valley . Curve a: vegetation on Furnace
Creek fan . Curve b: Funeral fanglomerate . Curve c: smooth salt unit.Curve d: rough salt unit.
Fig. 7. Low-altitude air photograph of Furnace Creek fan showing mesquite trees occupying drainages at lower right. Area shown is at D3 - E3
in Fig. 5.
Another alluvial fan at Tucki Wash is at the lower left
of the images (A7-D7). This fan illustrates the differences
in radar returns from alluvial surfaces of differing age.Three gravel units have been mapped here on the basis of
age (Fig. 5(e» [12]. The two youngest represent active
and recently abandoned washes. Both are relatively bright
at all polarizations because they are very rough at deci
meter to meter scales. The older surfaces, however, are
dark in all of the polarizations. These surfaces are com
posed of the interlocking mosaics of pebbles that formdesert pavement, shown in Fig. 8. Their smooth surfaces
result in specular reflection away from the radar antenna.
Work is ongoing to evaluate the consistency of age effects
on multi polarization radar images of alluvial surfaces in
arid areas.
Between the alluvial fans lies the lowest part of Death
Valley where salts have accumulated from the evapora
tion of lakes that once occupied the valley. These deposits
are zoned such that the center of the valley is composed
of halite (NaCl) surrounded by less soluble carbonates and
sulfates. The dark area in the center of the valley is the
seasonally wet flood plains which are very smooth andoften covered with a thin veneer of salt. The halite de
posits have been divided into rough and smooth facies [12]
251
Fig . 8. Field photograph of smooth desert pavement surface represented
by dark areas at A /B7 in Fig . 5. Scale is 15 cm long.
Fig. 9. Field photograph of rough salt unit. Unit is composed of silt andsodium chloride that have been eroded into a surface with microrelief upto 0 .5 m. This unit is best seen at H5 in Fig. 5.
which are most distinct in the cross-polarized image at H5
and 04, respectively. They are blue-white and greenishorange in the color composite, and curves c and d of Fig.
6 also show the differences in their polarization signa
tures. The distribution of these signatures closely matches
that of the geologic map (Fig. 5(e». The relatively high
VH return from the rough salt unit is probably the result
of multiple scattering from the extemely rough surface
shown in Fig. 9. The polarization response of the smoothsalt unit, when compared to that of the rough salt unit, is
unusual in that it has much lower VH return, and slightly
lower HH and VV returns. The difference between the
like and cross-polarized returns of the two units may be
due to high moisture conditions causing the smooth salt
unit to have an anomalously high dielectric constant. The
margins of the valley floor are the areas where ground
water from the alluvial fans usually surfaces. Thus, these
are commonly wet or marshy. This may be the cause of
the green color of the smooth salt unit at 04 and around
the base of the alluvial fans. However, because the im
ages are uncalibrated, it is not possible to quantify this
effect. Similar signatures are observed for marshy areas
of the Savannah River Swamp discussed later.
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252 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. GE-24, NO.2, MARCH 1986
B. Mapping Sedimentary Rocks
One of the main goals of geologic mapping in a sedimentary basin is to delineate changes in rock type that
relate to changes in paleoenvironment. Models of depo
sitional history are not only useful for exploration for
minerals, and oil and gas, but are important for determination of landslide potential and identification of potential
aquifers for ground water.
As part of a larger study headed by H. Lang (JPL) to
evaluate the utility of remote-sensing measurements for
mapping in a sedimentary basin environment, multipolar
ized airborne SAR images were acquired over a portion
of the Wind River Basin in central Wyoming. These im
ages, which are shown in Fig. 10, cover the Deadman
Butte area on the west flank of the Casper Arch. The strati
graphic sequence exposed in this area ranges from Trias
sic to Late Cretaceous in age and includes limestones,
siltstones, shales, and sandstones. The oldest unit exposed in the area covered by this image is the Sundance
Formation at Al-7. The Sundance is made up of nonre
sistant and resistant members labeled ISs and IS , in Fig.
10( e). The nonresistant member is a shale unit and ap
pears dark in all polarizations because it weathers to out
crops that are smooth on the scale of the radar wave
length. The polarization signature of this unit (Fig. 11),
however, is very different from the other shale units in
this area owing to compositional differences. Specifically,
this shale unit contains more organic material and clay
than the Mowry and Thermopolis Shales described below.
The resistant member of the Sundance Formation ap
pears fairly bright and slightly reddish in the color com
posite at A6 and A 7. This strong response is caused by
the very blocky nature of this unit. The slight pinkish tone
results from a slightly high cross-polarized return (Fig.
11). This is most likely caused by the vegetation cover
that this unit supports (Fig. 12). The dark parallel lines
that can be seen in the Sundance Formation at A 7 are small
horsts and grabens that have resulted from normal faulting
[13]. These structures expose a smoother unit with a lower
backscatter than the Sundance.
The Morrison and Cloverly Formations are both made
up of interbedded sandstones and shales and are difficult
to separate in this area [13]. However, variations withinthese formations are easily visible on the color composite
SAR image. For example, the slightly pink shade in the
color composite at B6 corresponds to an area of resistantsandstone that is similar in outcrop morphology and
vegetation cover to the resistant Sundance unit. The similarity between these units is also seen in their polarization signatures shown in Fig. 11.
The Thermopolis Shale overlies the Cloverly Forma
tion. This unit is easily mappable where drainages are accentuated (e.g., B/C4, 5, E7). The dissected morphology
and the low radar backscatter from this unit make this
readily interpretable as a nonresistant, easily eroded unit(Fig. 13). In addition, the polarization signature of theThermopolis Shale is very similar to that of the overlying
Mowry Shale (Fig. 11). These two units are very similar
in composition and are both quartz-rich.
The youngest unit exposed in the area covered by thisimage is the Frontier Formation (E-H, 1-5). This unit has
a relatively higher cross-polarized than like-polarized re
turn which results in a red tone in the color composite
(Fig. 1O(d». However, unlike the Cloverly and Sundanceunits, based on airphoto analysis and field work, this rel
atively high cross-polarized return cannot be related to
vegetation cover since only sparse, dry grasses are found
in this area (Fig. 14). Thus, it may be possible that the
cross-polarized return is dominated by scattering from the
subsurface.
A basal member of the Frontier Formation is also sep
arable on the color composite. Owing to the similarity in
polarization signature between this unit and the Thermo
polis and Mowry Shales (Fig. 11), one would expect this
basal unit to be compositionally more similar to those units
than to the remainder of the Frontier Formation.
C. Mapping in a Forested Environment
The Savannah River Plant (SRP) site covers some 780
km 2 of the upper coastal plain in western South Carolina.
The site has level to gently rolling topography, with low
relief, and a substrate of gently dipping Tertiary and Cre
taceous sediments. It is mostly forest covered. The natu
ral composition of the forest is closely governed by the
availability of moisture to the trees, and by the extent and
duration of flooding. The forest habitats range from very
dry sandy hilltops to continuously flooded swamp [14].
The range of habitats is divided into zones that are char
acterized by a community of tree species.
Simultaneous like-polarized (HH and VV) and cross
polarized (HV and VH) airborne SAR coverage of the SRP
site was acquired in March 1984. Polarization effects
should be mainly related to the forest cover, as geologic
and topographic variations in the area are relatively neg
ligible. The like-polarized images are shown in Fig. 15(a)and (b). The cross-polarized image is shown in Fig. 15(c).
The area of interest in this study extends from A3 to H3,
through H7 and A 7 on the image grids. The radar re
sponses in the HH, VV, and VH polarizations are com
bined to form a color composite image (Fig. 15(d». This
false color image enhances the relative inputs of the threepolarizations, and reveals colors that are related to majordifferences in the forest cover. Polarization signatures of
some units also have been displayed graphically (Fig. 16).
Most notable are the relatively bright returns in each
polarization from the Savannah River swamp area (A3 andH3 and A4 to H4). The swamp supports a dominant cypress-tupelo community, in a standing-water environ
ment (Fig. 17). Reflections from the tree and water sur
faces provide strong responses in each polarization. Thecombined input is strikingly displayed in pale yellow tones
on the color composite image (Fig. 15(d». Fig. 16 shows
in graphical form the relatively high returns with a slightdeficiency in VH.
Returns from the Pen Branch delta (D4-E4) are not
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EVANS el al.: RADAR IMAGES FOR MAPPING AND DISCRIMINATION
(a)
• ILLUMINATION~
(c)
(e)
EXPLANATION
I ( I ~ UPI'ER FkONTIER FORMATION
Kil LOWER FRONTIER FORMATION
11m MOWRY FORMATION
lit THERMOPOLIS FORMATION
KIm CLOVEI'll'!' AND
MORRISON FORMATIONS
J., NON RESISTANT MEMBER
OF SUNDANCE FORMATION
.... RESI$TANTMEMBER
OF SUNDANCE FORMATION
253
o lkm
~ k m (Al lt.fUII Il
Fig. 10. Multipolarization images of Deadman Butte, WY, centered on 43 °22 'N 106°58 'W. Images acquired September I , 1983. (a) Like polarization(HH). (b) Like polarization (VV). (c) Cross polarization (VH). (d) Color composite (HH = green, VV = blue , VH = red). (e) Geologic sketch mapof Deadman Butte area simplified from [13]. Locations of field photographs (Figs . 12- 14) are also shown.
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IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. GE-24, NO.2, MARCH 1986
zc
220 ,-------,----------,
180
~ = = - - - - - v - - - c : : : : : . . - . . . . , = _ ~ JS rKim
60L-______ -_____LHH • GREEN LVH • RED LVV • BLUE
II. Polarization signatures of units in Wind River Basin. Explanation
is the same as Fig. ID(e).
12. Field photograph taken looking south to the resistant member of
in Fig. ID(e).
of the Thermopolis Shale. Location shown in
Fig. lD(e).
of the adjacent
image yields a distinct yellow tone onb of the polarization
Fig. 14. Field photograph of the basal Frontier Formation. Picture loca
tion shown in Fig. ID(e).
sponse of the Pen Branch delta. The delta is an area of
nonpersistent emergent marsh. Much of the vegetation
cover has been killed by the elevated temperature of effluent waters that are drained via Pen Branch to the
swamp.
Islands in the swamp, and levees along the Savannah
River (e.g., B4-C4, E4-H4, and parallel to the river in
A3-H3) are elevated very slightly above the level of the
swamp. The small variation in elevation strongly affects
the kinds of trees present, and permits a different com
munity that includes species of maple, sweetgum, and
pine. This community produces relatively stronger re
sponses in VH and HH polarizations resulting in distinc
tive blue and reddish-blue tones on the color composite
image (Fig. IS(d)).The area north and east of the swamp (AS and HS
through H7 to A 7) has an extensive cover of managed
pine plantations. An example of a pine stand where the
pines are predominantly longleaf species is shown in Fig.
18. Relatively bright responses in the VH polarization
from this area produce predominantly blue tones on the
color composite image. Local areas of stronger response
in the HH polarization (e.g., at E6, E7, G7) show more
reddish tones on the color composite image. Fig. 16
graphically shows the comparison between these two sig
natures. Virtually the only difference is in the HH re
sponse. Preliminary field observations in the area, andcomparison of the radar images with corresponding color
infrared images that were acquired on the same mission
indicate that the relatively low HH response (blue) cor
responds to areas of dense pine canopy, and relatively
stronger HH response (reddish tones) corresponds to open
pine plantations with grassy understory. This indicates
that the type and intensity of polarization response varies
with the structure of the canopy. More detailed quantita
tive relations between polarization response and under
story, relative height (age) and density of the pine stands,
and contrasting responses of mixed hardwoods are topics
that are currently under investigation in conjunction withD. Wickland (JPL), and R. Sharitz (Savannah River Ecol
ogy Laboratory).
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EVANS el al.: RAuA R IMAGES FOR MAPPING AND DISCRIMINATION
(a)
(C )
o 1km
\;I '-lUIH
o tkm
(e)
(b)
(d)
~ k m {. \ / I UU l l n
o 1km
A/U.fU THl
255
Fig. 15 . Multipolarization images of Savannah River swamp , SC , centered on 33 °08 ' N, 81 °43'W . Images acquired March I , 1984; (a) Like polarization
(HH) , (b) Like polarization (VV), (c) Cross polarization (VH), (d) Color composite (HH = red, VV = green, VH = blue). (e) Sketch map of
Savannah River Plant area showing location of major features and field photographs (Figs. 17-19).
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256 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING. VOL. GE-24. NO . 2. MARCH 1986
250, - ------- ,--------" l
210
zo
170
f ~ ~ - - - - - - ~ ~ C - -
90'---_ _ _ _ _ '-_ _ _ _ _ - - '
LHH "RED LVH"BLUE LVV"GREEN
Fig. 16. Polarization signatures of units in the Savannah River Plant area.
Curve a: Savannah River Swamp. Curve b: Pen Branch Delta. Curve c:
dense pine forest. Curve d: open pine plantations with grassy understory .
Fig. 17. Field photograph of cypress-tupelo community in standing water.
taken at D4 . in Fig . 15.
Fig. 18. Field photograph of longleaf pine and some slash pine in managed plantation . taken at E6/F6 in Fig. IS . This area appears blue in the
color composite (Fig. 15(d)) .
A mixed hardwood forest is found on the moist soils
that are associated with small streams and old floodplains.
When the radar images were acquired in March 1984, thehardwood trees were not leafed out and in some areas the
soils were saturated. This results in a mottled pattern of
Fig. 19. Field photograph of clearcut taken at D6 in Fig. IS.
bright HH and VV responses, mostly in the area from A5
to D5 and A6 to D6. The pattern is virtually imperceptible
on the VH image (Fig. 15(c». This produces reddish-yel
low tones on the color composite image (Fig. 15(d».Cross-polarized returns are significantly lower than in the
swamp areas described above.
Clearcuts such as the one shown in Fig. 19, and open
water produce dark tones in all polarizations. Areas of
pine regrowth in the clearcuts yield relatively higher HHreturns. Such areas appear in dark reddish tones on the
color composite image (e.g., at C7 and G6). The margins
of the clearcuts that face toward the radar illumination
show stronger responses in the HH polarization (Fig.
15(a». This may be due to reflections between the trunks
of the pines and adjacent clearcut surfaces. Some small
ponds (Carolina bays) that are located mostly in the areafrom A 7 to G7 on the images have a concentric vegetation
pattern. Where the ponds are surrounded by trees, the
sides of the trees that face the radar illumination produce
very bright responses in both HH and VV polarizations
probably for the same reason as the forest-bounded clear
cuts.
V. CONCLUSIONS
Images from portions of Death Valley, California, Wind
River Basin, Wyoming, and Savannah River Plant, South
Carolina, show that multiple polarization data aid in mapping surficial deposits, mapping sedimentary rocks, and
mapping in forested environments, respectively.Multiple polarization radar data for Death Valley pro
vided a valuable tool for the study of alluvial surfaces of
different ages and lithologies, and of evaporite deposits of
different types and moisture contents. In the Wind River
Basin area, multiple polarization radar data were used to
discriminate sedimentary rocks based on surface rough
ness, vegetation cover, and possibly compositional infor
mation provided in the images. In the Savannah River
Plant area, brightness in the multipolarization images was
found to be qualitatively related to tree size, distributionand density, and to presence or absence of standing water
beneath the canopy. Further investigations are directed to
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EVANS et 0/ .: RADAR IMAGES FOR MAPPING AND DISCRIMINATION
relations between polarization responses, soil moisture,
and understory.
These results are particulary relevant to the Shuttle Im
aging Radar-C currently scheduled for 1989, which will
have multiple polarization capability.
ACKNOWLEDGMENT
The Aircraft Radar Group at JPL, headed by W. Brown,was responsible for acquiring the radar images presented
here. The Radar Systems Science and Engineering Group
at JPL, headed by D. Held, was responsible for the digital
processing of the data. We gratefully acknowledge their
contribution to this work. H. Lang, of the Geology Groupat JPL, provided one of the ground photos of the Dead
man Butte area.
We thank C. Elachi and D. Held for their helpful re
views of this manuscript, and the NASAlARC Medium
Altitude Missions Branch for their support of our efforts
via the excellent operation of the NASAlARC CV -990
Airborne Laboratory, Galileo II.
Note: On July 17, 1985, the NASAIARC CV-990
caught fire on takeoff from March AFB, CA. The crew
escaped without injury, but the aircraft, with the JPL ra
dar on board, was completely destroyed. The radar is
being rebuilt with the same parameters, and plans call for
it to be mounted on a replacement aircraft by mid-1987.
REFERENCES
[I] G. R. Valenzuela, "Depolarization of EM waves by slightly rough
surfaces," IEEE Trans. Antennas Propagat ., vol. AP-15, pp. 552-
557, 1967.
[2] A. 1. Blanchard and 1. W. Rouse , Jr. , "Depolarization of electromagnetic waves scattered from an inhomogeneous hal f space bounded
by a rough surface," Radio Sci., vol. 15, pp . 773-779,1980.
[3] R. N. Colwell, Ed., Manual of Remote Sensing. American Society
of Photogrammetry, 1983.[4] A. K. Fung and H. 1. Eom, "Note on the Kirchoff rough surface
solution in backscattering," Radio Sci., vol. 16, pp. 299-302, 1981.[5] T. W. Thompson, "A user 's manual for the NASA /JPL synthetic
aperture radar and the NASA/JPL L- and C-band scatterometers, "
JPL Pub. 83-38 , 1983.[6] A. Kozma, E. M. Leith, and N. G. Massey , "T i lted plane optical
processor," Appl. Opl., vol. II , pp. 1766-1777, 1972.[7] C. Wu, "Modeling and a correlation algorithm for spaceborne SAR
signals," IEEE Trans. Aerosp. Electron . Syst., vol. AES-18, 563-
575, 1982.
[8] M. Jin and C. Wu , "SAR correlation technique-A modified inter
pretation algorithm," in Proc. IGARSS , 1983.[9] K. Tomiyasu, "Tutorial review of synthetic aperture radar (SAR) with
applications to imaging the ocean surface," Proc. IEEE, vol. 66, pp.563- 583 , 1978.
[10] C. Elachi, T. Bicknell, R. L. Jordan, and C. Wu, "Spaceborne synthetic aperture radars: Applications, techniques , and technology , "
Proc. IEEE, vol. 70, pp. 1174-1209, 1982.
[II] G. G. Schaber, G. L. Berlin, and W. E. Brown, Jr., "Variations in
surface roughness within Death Valley, California: Geologic evalu
ation of 25-cm-wavelength radar images ," Geol. Soc. Amer. Bull. ,
vol. 87, pp. 29-41 , 1976.[12] C. B. Hunt and D. R. Mabey, "Stratigraphy and structure, Death
Valley, California," U.S. Geol. Surv. Prof. Paper 494-A , 1966.[13] T. C . Woodward, "Geology of Deadman Butte Area, Natrona County,
Wyoming," Bull. Amer. Assoc. Petroleum Geol., vol. 41, pp. 212-
262, 1957 .[14] T. M. Langley, and W. L. Marter, "The Savannah River Plant site,"
E.!. Du Pont DeNemours and Co. , Savannah River Lab., Aiken, SC,DP-1323 , 1973 .
257
Diane L. Evans received the A.B. degree in geology from Occidental College, Los Angeles, CA,
in 1976 and the M.S. and Ph.D. degrees in 1978
and 1981 , respectively , in geological sciencesfrom the University of Washington , Seattle.
She is currently a Member of the Technical
Staff in the Radar Sciences Group and the Assistant Program Manager for the Land Processes
Program at the Jet Propulsion Laboratory . She is
the Principal Investigator for a study of new techniques for quantitative analysis of SAR images and
a Collaborator for a Shuttle Imaging Radar-B (SIR-B) study of the quantitative use of multi-incidence angle SAR for geologic mapping. She was
part of the operations team during the SIR-B mission in October 1984, and
is presently serving on the RADARSAT Science Working Group and asthe Experiment Scientist for SDR-C.
*Tom G. Farr (M'84) received the B.S. degree in
1974 and the M.S . degree in 1976, both in geology from the California Institute of Technology,
Pasadena , and the Ph .D. degree in 1981 in geology from the University of Washington, Seattie.
Throughout his Masters and Ph.D. work, he
was employed by the Jet Propulsion Lab, at first
working on airborne radar data of arctic sea iceand later on Seasat and SIR-A images of geologictargets. He is currently an Investigator on the SIRB experiment, which has involved the develop
ment of new techniques for the extraction of quantitative geologic infor
mation from multi-incidence angle radar images. His current research in
terests include the improvement of electromagnetic scattering models forrough geologic surfaces and subsurfaces, and the use of multiparameter
radar systems to quantitatively predict surface and subsurface propelties on
Earth and other plane ts.Dr. Farr is a member of the SIR-C Science Working Group in geology.
*J. P. Ford (S'78-M'82) received the B.Sc. de
gree with honors in geology from the University
of London, England, in 1959 and the Ph.D degreein geology from The Ohio State University, Co
lumbus, in 1965.He has worked at the Jet Propulsion Labora
tory , California Institute of Technology, Pasa
dena, since 1977, as a Senior Resident Research
Associate (1977-1979), Membcr of Technical
!I Staff (1979-1981), Technical Group Leader(1981-1982), and Supervisor (1982 to the pres
ent) in the Radar Sciences Group , Earth and Space Sciences Division. Hisresearch interests are currently directed in the area of radar remote sensingfor geologic mapping, with particular application in forested environments.
*Thomas W. Thompson (S'58-M'80) was born in
Canton, OH, on May 25, 1936. He received theB.S . degree from Case Institute of Technology in1958, the M.E. degree from Yale University in
1959, and the Ph.D. degree from Cornell Univer
sity in 1966.
He was one of the first experimenters to use the430-MHz radar at the Arecibo Observatory. From
1964 through 1969, he made extensive radar observations of the Moon. From 1970 through 1976,
he was a coinvestigator on the Apollo LunarSounder and was a principal investigator on one of the first lunar data synthesis programs. From 1973 through 1981, he participated in the Seasat
program and also served as Science Operations Coordinator on the Voyager
mission. Since 1983 he has coordinated the NASA /JPL Aircraft SAR pro
gram.
*C. L. Werner, photograph and biography not available at the time of pub
lication.