r""<""-----------------,9·37'
ANDRIS VIKSNE*
THOMAS
C.
CECIL
LISTON
D.
t
SAPPt
Raytheon/ A utometn·c
Alexandria, Va. 22304
' - - - - - - - - - - - - - - - - - - ' ' ' - - - - ' 7·N
77·
83·
so
100
ISO
Mile,
FIG. 1. Index Map.
SLR Reconnaissance of Panama
Although not replacing conventional aerial photos,
radar imagery has some distinct advantages. **
INTRODUCTION
IDE-LOOKING RADAR (SLR) was first
developed for military targeting purposes
in the early 1950's. It soon became obvious
that such radar imagery would be capable of
S
SLR can be considered a geophysical tool in
that it provides a measure of the reflectance
characteristics of the overflown terrain, the
results of which are displayed as an image
resembling an optical photograph but having
SLR (Side-Looking Radar) was successfully used in lieu of optical
photography for reconnaissance of the Darien Province of Panama and parts of
Northwest Colombia, and for the construction of geoscience products thereof.
A nAN/ APQ-97 side-looking radar was used to produce high-resolution
imagery of an area containing approximately 6,600 square miles in 4 hours of
flying time-an area, furthermore, that is almost perpetually cloud covered.
The SLR imagery was used to prepare an uncontrolled mosaic and a series of
geoscience overlays, including: Surface Drainage, Surface Configuration,
Vegetation, Engineering Geology. The results of this study are believed to be
unique in that they provide the first complete overview of Darien Province,
thereby demonstrating the capability of SLR to gather geoscience data in an area
that is notorious for the d(fJiculties that its persistent cloud cover poses for the
acquisition of usable conventional optical aerial photography.
ABSTRACT:
providing significant military geographic intelligence. As radar systems became more
sophisticated and imagery resolutions improved, it was natural that SLR should also be
suggested for non-military applications in
terrain reconnaissance surveys.
* Formerly with Raytheon/Autometric, now
Bureau of Mines, Washington, D. C.
t Formerly Raytheon/Autometric, now with
Control Data Corp., Minneapolis, Minn.
t Raytheon/Autometric.
** See also "Radar Mapping in Panama" by
C. J. Crandall in PHOTOGRAMMETRIC ENGINEERING, June 1969, page 641. This article is reprinted
by permission from Geophysics, Vol. 34, o. 1, pp.
55-64, February 1969.-Editor.
lower resolution. Basically, radar imagery
represents a record of the interaction of
transmitted electromagnetic waves with nonuniform natural surfaces of the terrain. Soil
and plant moisture content, dielectric properties of rock and soil, vegetative cover, surface roughness, geometry and penetration
characteristics of the particular frequency at
which the radar is operated are the most
significant parameters affecting the radar
return.
In addition to its capability of providing
wide areal coverage in a minimum amount of
flight time, operation of a SLR system is al-
253
254
PHOTOGRAMMETRIC ENGINEERING
most independent of diurnal/and atmospheric
conditions owing to its being an active sensor
(i.e., it transmits electromagnetic waves,
thereby providing its own illuminating
source), and to the fact that these waves are
sufficiently long to penetrate cloud cover of
all but the cumulonimbus type. Thus, the
system has a day/night and all-weather
capability.
Project RAMP (Radar Mapping of Panama)
was initiated in 1965 by the U. S. Army
Engineer Topographic Laboratories (formerly
USAE-GIMRADA) to demonstrate the capability of the AN / APQ-97 SLR system to produce high resolution radar imagery to be used
in lieu of optical photography. The Darien
area of Panama chosen for this operational
test consists of about 6,600 square miles
(Figure 1). Once-over coverage, with overlap,
was obtained in approximately four hours
flying time with a YEA-3A aircraft carrying
the radar system at an average ground speed
of 350 knots.
A primary consideration in the selection of
Darien Province as a test area lies in the fact
that it has a near-perennial cloud cover that
severely limits the acquisition of conventional optical aerial photography. The results
obtained by this SLR experiment are considered unique, inasmuch as the acquired
imagery provided the first complete overview
of the Darien. Prior to this experiment,
persistent and unsuccessful attempts had
been made for nearly twenty years by the
U. S. Air Force and numerous private contractors to acquire optical photography of
the area.
SENSOR CHARACTERISTICS
The AN/APQ-97 is essentially a bruteforce radar system operating in the K band.
I t has better than a 99 percent cloud penetration capability, but does not, however,
penetrate heavy rain or vegetative cover. The
high-resolution imagery is recorded in a
slant-range presentation in which the scale
increases with distance from the aircraft
ground track. The sweep is down and to one
side of the aircraft (Figure 2).
PROCEDURES AND RESULTS
I n order to acquire stereoscopic and crossflight coverage, a total of six missions were
flown over the subject area from various
directions. After eight of the best parallel
flight strips were selected, an uncontrolled
mosaic (Figure 3) was constructed to the
scale of 1 :250,000. This was subsequently
Al TITUDE
GROUND
TRAe K
~/S~
~14r
S
.< '
~O
FIG. 2. SLR sweep characteristics.
reduced to a scale of about 1:750,000 for
facility of inclusion in this paper.
The approach used to establish the value of
SLR imagery in the extraction of geoscience
data involved the preparation of a series of
overlays registered to the mosaic, each addressing a specific topic.
A number of overlays to the mosaic were
prepared from interpretations of the SLR
imagery, and four of these have been selected
for discussion in this paper. These include:
Surface Drainage, Surface Configuration,
Vegetation, Engineering Geology.
SURFACE DRAIN AGE
One of the most val uable tools available in
reconnaissance terrain studies, particularly in
areas of low-to-moderate relief, is the regional
and local expression of the surface drainage.
The recognition of variations in the distribution patterns, differences in drainage
density and texture, depth of channel incision, etc., permit inferences to be made concerning structural and compositional conditions of the underlying terrain.
Drainage features are particularly welldefined in SLR records. Bodies of water give
the appearance of black, or no-return areas
because of their smooth, horizontal surfaces.
Black areas on imagery are due either to nonreflectance of materials or to reflectance away
from the receiving antenna. Any surface
whose roughness is less than half the wave
length of the SLR system acts as a specular
reflector, whereas surfaces whose roughness is
greater than half the wave length act as
diffuse reflectors. Drainage patterns are
further defined both by their continuity and
by the fact that the radar energy rebounds off
the banks and marginal vegetation of drainage channels, producing a brightly defined
SLR RECONNAISSANCE OF PANAMA
FIG.
255
3. Radar mosaic of Darien and Northwest Colombia.
edge. The resulting contrast facilitates the
delineation of such areas.
Drainage patterns are diagnostic of specific
terrain conditions. To varying degrees they
are capable of suggesting the nature and
depth of soil cover, lithology, morphology,
and the structural and tectonic influences
FIG.
prevailing in the area. The patterns present
themselves in an infinite variation of density
and habit, the density being mainly determined by the lithologic character of the rock
traversed, i.e., hardness, porosity, solubility,
and consolidation, whereas the habit is
determined primarily by structure, i.e.,
4. Surface Drainage.
256
PHOTOGRAMMETRIC ENGINEERING
FIG. 5. Surface Configuration. (1) Plains; relief generally less than 50 m. (2) Low hills; relief generally 50 to 150 m. (3) High hills; relief generally 150 to 600 m. (4) Mountains; relief generally more than
600 m. Local geomorphic features: Pu, upland plain; Pc, coastal plain; Pi, interior plain; Pa, alluvial
plain; ox, oxbow lake; de, delta; 19, lagoon; be, beach; ob, offshore bar; nl, natural levee; tf, tidal flats; fP,
flood plain.
faults. fractures, and the attitude of bedding.
Thus, the drainage pattern overlay, as shown
in Figure 4, was the first to be developed from
the imagery and was thereafter used as a base
for other overlays.
Some differences were noted between the
SLR imagery and existing maps of the area.
Most notably, the course and direction of
flow of one of the rivers were incorrect on all
maps examined. Many other minor examples,
mostly changes in character of shoreline or
drainage features, were noted. Although some
of these differences might possibly be attributed to recent changes in the stream pattern,
the existing coverage maps being quite old,
most differences weIe the result of limited
photo coverage and lack of detailed grou nd
information concerning the area.
SURFACE CONFIGURATION
SLR records are an excellent medium for the
portrayal of regional landforms owing to the
continuity afforded by the wide, long image
segments. The generalizing ability of SLR,
which permits the elimination of superfluous
detail, provides the interpreter with a synoptic view that allows him to make quick judgements without, however, obscuring the
presentation of major landforms.
The elements most useful in the interpretation and analysis of landforms on AN/ APQ-
97 records are topographic expression and
drainage patterns. The characteristics of a
landform depend primarily upon its composition, morphology, and structure, the climate
in which it was formed, and the various
erosive processes.
As outlined in Figure 5, the regional geomorphic features of Darien consist of Plains,
Low and High Hills, and Mountains. This
classification of landforms was made on the
basis of local relief, which is defined as the
"difference (in elevation) between (the)
highest parts of interstream areas (or with
mountains, the crests) and the adjacent
valley bottoms."
As was the case with the drainage and
coastal features, substantial differences were
observed between the SLR presentation of
landforms and their portrayal on existing
maps of the area. One such difference is the
location and orientation of one of a series of
hills east of the Tuira River and inland from a
major swamp area (near the center of the
mosaic). The major axis of this anticlinal
hill is shown on earlier maps to be aligned
approximately NW-SE instead of NE-SW as
shown in the radar imagery. Previous maps
of this specific area were made by ground
surveys with no aerial photographic coverage
available to serve as a check.
Some other outstanding differences ob-
SLR RECONNAISSANCE OF PANAMA
INVISIBU
OBJECT
OBJ Eel
FIG. 6. Radar-produced shadow effect.
served were the character of coa~tlines, the
alignments of minor ridge~, and the alignment
of the Continental Divide. In addition,
numerous minor topographic expres~ions on
the plains appeared on SLR but were not
found on any maps.
VEGETATION
As stated previously, under Sensor Characteristics, the K-band SLR does not penetrate
vegetative cover, thus making it possible to
evaluate the various vegetation forms on the
basis of their reflectance characteristic~. Of
257
course, a general knowledge of the vegetation
associations existing in the particular geographic location of the imagery, and the
knowledge of the time of year the imagery
was obtained, are necessary before any assessment of specific gray tones and textures, in
terms of particular vegetation types, is
possible. 1n the high-relief zones of the subject area, the varying tones of gray that
reflect distinct changes in vegetation were
sometimes obscured by the "shadow effect"
inherent in the SLR system. That i~, the
steep surfaces directly exposed to the sensor
show up much brighter than the surrounding
area while the opposite side of such protrusions, of course, lay in a shadow area
(Figure 6). An additional difficulty in delineating vegetation strata in the high-relief
;ueas was due, not to the radar system, but to
the heterogeneous nature of the vegetation
types found. Distinct boundaries between
the Evergreen Rain Forest and the Mixed
Semi-Deciduous and
Evergreen
Forest
(Jungle), for example, could not be discerned
on the imagery since these two zones (and
other forest zones) blend into each other
gradually over a distance of from several
hundred meters to several kilometers. Thus,
no distinct boundary exists.
I n such areas the best j udgmen t of the
FIG. 7. Vegetation. Tropical forests: (1) Evergreen rain forest; (2) Mixed semi-deciduous and evergreen
forest (jungle); (3) Sub-montane forest; (4) Palm forest. Wetlands: (5) Swamp with low tre~s; (6) Fresh
water or brackish swamp with tall trees; (7) Coastal mangrove swamps; (8) Marshes. Cultivated c!earings: (9) Mixed crops scattered small plots (including abandoned areas in regrowth); (10) PlantatIOns.
Non-cultivated clearings: (11) Lumbering; *Settlements.
258
PHOTOGRAMMETRIC ENGINEERING
Gill
"
• • • AM ....
I~::::~::t~-q
E:-'l,"';) Igneous Rocks
Anticlinal Axis
-I
Synclinal Axis
+-
Plunging Anticline
-I--
Plunging Syncline
-+-
Sedimentary Rocks
D
Strike and Dip
Unconlolidated Deposits
Fault
(,::oncealed or inferred)
Fractures and lineaments
(dips not determined)
Dike
Fault (showing dip)
Escarpment
(over 60% slopes; over
5 meters high)
FIG.
8. Engineering Geology.
interpreter is based on an "averaging" of the
transitional zone for boundary placement.
Some larger-scale aerial photos and local spot
photography aided somewhat in the delineation of these di fficul t areas.
The vegetation overlay (Figure 7) delineates the major forest types, wetlands,
grasslands, and clearings.
ENGINEERING GEOLOGY
SLR imagery is a tool particularly wellsuited for use in the regional interpretation
and mapping of folded mountain, plain, and
plateau areas. The broad coverage accomplished through side-scanning and strip
recording provides a view of large areas and
permits continuous interpretation of the
radar image. This is not possible with conventional aerial photography without extensive mosaicking. Regional features are
easily recognized and associated with other
significant units necessary for an accurate
areal evaluation. Aerial photography usually
presents only a segmented view of regional
features, making rapid analyses difficult.
Hard, resistant beds of sedimentary or
igneous origin are easy to follow on the SLR
records. Coarse clastic materials (thick sandstones, conglomerates, quartzites, etc.), with
uniform image tonality and constant resistance, can be mapped continuously for many
miles. Ridges produced by resistant beds are
usually immediately apparent and can be
easily traced.
The major structural features of the area,
and the structural attitudes of specific rocks
in localized areas, were determined from the
imagery by evaluation of topography, outcrop, drainage patterns, and vegetation variations.
The Engineering Geology Overlay (Figure
8) includes major rock types categorized by
gloss engineering characteristics and shows
their areal extent. The symbols repre"ent
major geologic structural and litho-stratigraphic features in this investigation:
Igneous Rocks. Extrusive (Basaltic)-Andesite dominant, basalts common; medium to
fine-grained; gray, pink; massive; local irregular
fractures common. Generally in mountains and
hills; quarry sites difficult to reach; heavy blasting required; suitable for building stone, aggregate, riprap, base course, and surface course;
high bearing capacity; stable in steep slope;
overburden to 6 meters.
259
SLR RECONNAISSANCE OF PANAMA
Sedimentary Rocks. Undifferentiated-Stratified chert, crystalline limestone (with interbedded tuffs), sandy shale, sandstone and conglomerates; in low hills and broad valleys;
quarry site access difficult; light blasting required. Only hard sandstone, conglomerate and
limestone suitable for building stone, ri-rap,
aggregate, base/surface course; moderate bearing capacity. Others suitable for fill only. Modera tely stable in steep slope.
Unconsolidated Deposits. Stream alluviumUnconsolidated materials more than 6 m. thick
continuously covering bedrock. In plains,
beaches, river beds, swamps, marshes. Generally
unsuited for construction use except as fill; low
bearing capacity. Unstable in steep slope.
CONCLUSIONS AND RECOMMENDATIONS
This investigation has demonstrated some
of the geoscience capabilities of SLR. Although SLR has not eliminated the need for
conventional aerial photography, it has been
shown conclusively that radar imagery can
be utilized in lieu of photography:
• To provide imagery coverage required for the
preparation of recon naissance geoscience
products in remote, unmapped or poorly
mapped areas, especially those having nearly
year-around cloud cover of low-angle illumination.
• For the frequent and rapid updating of maps
and charts, and for acquiring general information about area.
• As an effective tool for the mapping of regional geology.
ACKNOWLEDGEMENTS
This work was performed under contracts
no. DAAK02-67-C-0167 and no. DAAK0267 -C-0316, for U. S. Army Engineer Topographic Laboratories, Fort Belvoir, Virginia.
The authors wish to express their appreciation to Messrs. J. H. Simons and R. F.
Pascucci for their helpful suggestions, and to
the Raytheon Company and the U. S. Army
Engineers for permission to publish this
paper.
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