Aerial radar imagery of highly faulted volcanic terrain in southeast Orego

Walker, G. W.

English

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TECHNICAL LETTER NASA-25
EVALUI1TION Or RADpk llr"nGERY OF HIGHLY FAULTED
VOLCANIC Z'ERt2ANE IN SOUTHEAST OREGON*
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Thesedata are preliniirtary and should
not be quoted t-Jitiicut permission
prepared by the Geological Survey
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for the National Aeronautics and(Idt15A)
space AulministratiOn
under NASA Contract Ito. R-09-020-01bperformed
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Evaluation of radar imagery of highly faulted volcanic terrane
in southeast Jregon
By George V1. 'dalkec
Introduction
Radar imagery, alone a singly east-viest overflight about 25 miles
north of the Oregon border and exterdiny from the Idaho border LU the
Pacific Ocean, is compared with recent geologic maps (Vlells and Peck,
1961; Walker, 1963, Walker and Repenning, 1965, 1966) mach by
reconnaissance and standard photogeologic methods for areas east of
the Cascade Range. Geology of a strip about 10 rules wide and 20 miles
long is interpreted from the radar image (approx. scale, 1:160,000) and
is compared directly with geology mapped and plotted on high altitude,
black-and-white photographs (approx. scale, 1:60,000).
Both polarized and depolarized imagery were obtained in
October 1965 from a radar system that operates in the K band. A image
recording the polarized (horizontal) component of the returned radar
signal and an image recording the depolarized (vertical) component
were obtained simultaneously. Apparently, much of the returned
signal remained polarized, and as a result the image recording the
depolarized (vertical) component of the signal shoves less contrast
and is less grainy than the polarized one; this affects both resolu-
tion and irrLerpretation of ground-surface features. Both polarized
and depolarized images are considerably distorted.
9Sin^;erely yours,
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UNITED STATES
17EPARTNIENT OF THE It^ITERIURf
GEOLOGICAL SURVEY
WASHINGTON. D.C. 20242
	 Technical Letter-
_-	 NASA -- 25
Hay 19LU
Dr. Peter CB iadgley
Chief, Natural Resources Program
Office of Space Science and Applications
Code SAR, NASA Headquarters
Washington, D.C. 20546
Dear Peter:	 I
Transmitted herewith are 3 copies of:
TECHI-41CAL LETTER IIASq-25
EVALUATION OF RADAR IMAGERY Ur HIGHLY FAULTED
VOLCANIC TERRANE IN SOUTHEAST OREGO: x-
by
G.W. Walker**
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(NASA CR OR TM% OR AD NUMBER) 	 (CATEGORY)
William A. Fischer
Research Coordinator for
USGS/NASA Natural Resources Program
lock perfcxmed under 11ASA Contract Nu. R-0 -020-01^)
^-*U.S. G--alogicai Survey, Menlo Park, California
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The radar strip crosses an area noted for very e;.-teaive '.iertiary
volcanism,including a uGtT^h-sough chain of inactive; or dormant a.ndesitic:
and daci tic volcanoes in the Cascade Range, revern -I La jor zilic: c vent
areas probably related to Miocene and Pliocene ascfloHs, several 'lame
volcano-tectonic depressions, well-developed Iiii.d-Tortiary aid youtlge:r
Basin and Range fault structurco, and extensive surfacer of basalt that
contrast with widespread sheets of welded tuff and tuffaccouG sediment.:-,y
rocks. Soil and vegetation cover vary widely from "teusive ba:ri, rock
outcrops to areas of deep soil and sparse to dense foxcLits.
Radar ima,ery
l7veluattioa of tile radar 3ma;;czy demonstrates that most phy Biographic
and some gaologic features, clew--i- f depicted on conventioncl aerial
photographs, also are well defined by radar. lni general, the Gcolog_c
features evident on the radar ii< bcs aro those - troaLly reflected by
topography. Tile degree of resolution and, hence, tine interpretive nature
of differelit surface features varies with the density of regetatiou cover
4
and with the character (polarization?) of the radar image, riost features
being more readily apparent on the	 horizoacally polarized
image whereas others are Lore easily seen ou the vc^^icz:cLly i^olxized
inaga. Score cultural features, including plowed fields, graded g_i•avel
or dirt roads. LiLeline r ;rn60  of w.-y, are darker and more clearly
defined on the depolarized image.
2
Large- and small-scale normal faults related to fault-block basins
or volcano-tectonic depressions are clearly evident on the radar inia,;u3,
and are particularly promiiLeht in untinibered areas oa the polarized
Linear scarps aiid valleys mark the position of many of the faults auu,
in areas of dense forest cover where: tupographie relief is partly obscured,
the radar imagery depicts some f the faults betLer than on conventional
photographs.
Some of the basins between major faults are filled with 'tine-grained,
poorly indurated, tuffaceous sedimentary ro,-ks which in places are water
saturated. They absorb much of the radar_ehcrgy so the images tend to be
darker than those or adjoining areas underlain by denser rock:; with little
or no water.
Several brighteL acid more highly reflective areas which Gouu<<only liave
dendritic drainage are present oa the east end of the radar strip. They
are underlain by widespread dacite or quartz latite flows w ita a disconLin'auus
veneer 1 cm to 1 m thick of grussy detritus composed of angular, well-sorted,
mostly equant rraglaents 0.5 cm or less in diameter. Iii wast places the
veneer of fragmental mat rial and the underlying flows are well drained and
•	 contain little water. The high reflecLivity of these areas may result
from the angular fragments in the surficial veneer, a(ting as corner
reflectors, from near-surface bedrock, from the luw water content of these
materials, or from a combination of the3o factors. Vo other sur acu feature3
which contrast basalt flOWS wiLh welded tuffs or tuffaceous sediments have
been recogniz.:d in the imagery.
3
Geologic analysis was made of an enlarged radar image (fig. 1) of
a small Lost area that includes hart Piountain--a complex hoist and a
major silicic veLiL area--aud parts of the adjacent, highly faulted
Warner Valley graben. The results (fig. 2) are compared with a &culogic
map (fig. 3) obtained by reconnaissance trave=rses and much I;itjLOgeulogy.
The radar image accentu:;tes some structures, particularly those marked
by pronounced topographic expression, so that many, but not all, fauli:s
are clearly depicted (fig. 2). Vertical separation, or apparoat offset,
is visible on some faults, but on others seems to be ubscured, partly
because of the grainy image. The radar image also shows Lhat :,ome ur
the rock units are distiactly layered and are probably well iudurated,
for they form large steep scarps. I-.ost of Lhe layered ;ocks seem to dip
less than 10° and are only slightly dufurwcd.
Nothing in the radar ii-aage, however, ittdicatos Lhat Llte area is
composed dominantly of volcanic rocks, includin- widespread basalt flows,
welded tuffs, rhyodacite flours, and small intrusives. In cuuLt:ast,
different lithologies shown on the geologic map (fib;. 3) are commonly
recognizable on high-alL'itude aerial photographs because of differences
in tonal contr4sL or because of distinctive patterned 6routid that
characterizes many basalt flows, some rhyodacitic flows, and some welded
tuffs. Thecc fealures and other comparable oncs that are impurtauL in
distinguishing the various rock types are not visible on the radar images.
4
Summary — - -- - -- —
	 - - - -
The synoptic vic:: -Eforded uy the radar image of southeast Oregon
is useful in tracing regional structures reflected by topoyraphy.
Geologic features are generally more apparent on the high-contrast 	 -
(horizontally) polarized image, although several cultural features
(plo,:ed fields, graded gravel or dire roads, a pipeline riolht-of-way)
are mo;e clearly delineated on the depolarizcd image. Comparison of the
radar image wi-ch conventional high-altitude photographs of ti,e saute 	 --
area indicates that the photographs supply considerably more complete
and detailed geologic information.' than sloes the radar image, perhaps	 -
partly because of the appreciable :tale dif erenco.
References
Walker, G. W., 1963, Reconnaissance geologic male of the eastern half of
the Klamath Falls (At'S) quadrangle, Lai<e and Klamath Couuties,
Oregon: U.S. Geol. Survey Field Studies 14ap fY -2b0, scale 1:250,000.
Walker, G. W., and Repenning, C. A., 1965, Reconnaissance geologic map of
the Adel (X01,S) quadrangle, Lake, Harney, and Nlialheur Counties,
Oregon: U.S. Geol. Survey bliss. Gool. Inv. Map I-446 scale 1:2.50,000.
1966 ) Reconnaissance geoluyic map of the nest half of the Jordan Valley
(friS) quadrangle, Malheur County, Oregon: U.S. Geol. Survey Misc.
s
Geol. inv. Map I-4,7, scale 1:250,000.
Wells, F. G., ai;d Peck, D. L., 1961, Geologic map of Oregon Wrest of the
121st meridian: U.S. Geol. Survey E.iisc. Geol. Inv. flap MI-325,
scale 1:500,000.
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Evaluation of radar imagery of highly faulted volcanic terrain in southeast Oregon

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