Evans et al

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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



EVANS et al.: RADAR IMAGES FOR MAPPING AND DISCRIMINATION 247

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DATA PRODUCTIONL- __

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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



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



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.



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).



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.



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



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.



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).



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).



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



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.

Evans et al

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