)es on radar imagery
iration on LANDSAT
luous woodland and
| on radar is the
eral genera of
mangrove in Darien
'eturn, apparently
king network of
“igure 5) is repro-
of mangroves in
ired in other areas
signatures for
/egetation is from
'all configuration
'rom multiple reflec-
same manner that
jh in the field the
'edding within the
juter limits of the
/ large flat areas
;. A small area of
n but has yet to
je season dependent
is of young oil palms
nooth return (Figure
from the coconut
ars to be little
species (Figure 9a, b),
ture of the return.
| of the oil palms
11d also be considered.
such signatures
other environments.
tation. In a large
ists can be observed
ists may be related
/ shadowing along
ifferences in species,
irn when looking at
ivala and Ulaby, 1976;
^ vegetation types
it 3 cm (x-Band)
1 only one band of
splays the terrain
Such examples point not only to the need for extensive investigation and
documentation of unique vegetation signatures but also to the potential ulti-
mately sought for automated mapping.
Geologic Elements
An anticline in the Cretaceous sequence north of the Benue River in Nigeria
(Figure 10a-d) provides an excellent example of the importance of "dual opposing
looks" and shadowing in geologic mapping from SLAR imagery (Gelnett, Dellwig,
Bare, 1978). Within the core of the structure, thin resistant sandstone units
which can be identified on the SLAR images are defined primarily on the basis
of radar shadowing. Such units cannot be detected on the LANDSAT image. In a
similar manner, faults and joint patterns at the southwest and northeast ends
of the structure are prominent and in some instances detectable only on the
SLAR image. Whereas the shadowing enhances these structures, it may also
obscure the true position of a fracture occupying a topograhic low (Figure 3),
but which may be revealed with illumination from the opposite direction. In a
like manner thin sandstones within the core on the north side are shadowed in
by the south "look" image but revealed in the north "look" image. One can also
compare the radar image with the LANDSAT image (Figure lla-c) of several of the
many ring dike complexes southwest of Lere, Nigeria, and further document the
importance of shadowing in SLAR imagery. Comparison with distribution of
granite and granite porphyry lithologies in the Precambrian complex shown on
the geologic map of Nigeria, indicates the value of utilization of SLAR imagery
at reconnaissance scale for refining otherwise-obtained map data.
Recent generation (May, 1976) of radar imagery over the northwest shore
of Manila Bay (Bataan Peninsula) as part of a site selection study for a nuclear
power plant offered the opportunity of evaluating SLAR and LANDSAT imagery
(Figure 12a-c) for providing necessary geologic data in this earthquake-prone
area. On the basis of tone-texture signatures, good correlation between mapped
units and imagery units could be achieved with little difficulty. Lineaments
(in such an environment reasonably interpreted as faults) not previously mapped
were located. In contrast, correlation of units found on LANDSAT MSS imagery
with those on the geologic map was poor and the lineaments totally lacked
expression on the LANDSAT images. Texture on LANDSAT imagery in this terrain
which is dominated by relatively-unweathered young volcanics is subdued on
LANDSAT imagery because of the lack of rock contrast between the influves and
valleys, the lack of shadowing across valleys, and finally the nearly perpetual
cloud-shrouding of the peaks.
Radarmaps©
Radar imagery may also be reproduced in such a way as to provide a plana-
metric map format in which terrain elements can be easily and rapidly identi-
fied by the unskilled map reader (Figure 3). Maps of a similar nature have
been generated for years by European cartographers and more recently by the
U. S. Geological Survey, combining the topographic data of the traditional
map with a shaded relief presentation so that the configuration of the surface
is immediately obvious (Figure 4).
: With a built-in shadowing capability, a mosaic generated from SLAR
imagery enhances terrain elevation varaition in the same manner as does the
shaded relief map. Printed in brown or green with superimposed data derived