rtues of a cloud
ather, it will be
ated and presented
es the icing on the
r products, those
and cover data will
ensing that which is
corded near-infrared
ss and dielectric
c spectrum. The
objects on the basis
n the optical region.
n Louisiana, the
of deciduous and
pines (Dellwig and
ovides a high return
primarily because of
y a function of a
eve a degree of
e LANDSAT MSS. More
e-looking radar,
on angles, for example,
the object (Table 1).
] 15? Depression Angles
Length of Shadow
at 15? Depression
Angle in Feet
7.47
37.33
186.64
developed through
| increases the
rever, low depression
can be reduced with
range of the image
's of approximately
| Zero Delay
Mid-R SW Used
22?
14°
9°
60% essentially assures the placement of any terrain feature in a near optimum
position for examination. Particularly valuable in high relief terrain but
desirable under all conditions in all terrains are opposing "looks". Although
a single look may provide most of the desired data, it was demonstrated during
the evaluation of imagery from Darien Province, Panama, that each additional
look from a different direction provided some additional information (MacDonald,
1969).
Drainage Network
Exemplifying the value of shadowing combined with contrasts in signal
return is an area southwest of Atakpamé, Togo, West Africa (Figure 2a, b, c).
The riverain forest with tree heights up to 120 feet spans all orders of
streams shown in the image. Because the channels are completely obscured,
the LANDSAT Band 7 image which would normally be expected to present the water
bodies characteristically black, records the network only on the basis of a
contrast in response of vegetation occupying the valley with that of the adja-
cent savanna and fails to reveal lower order streams. On the radar image,
even neglecting contrast in canopy configuration and dielectric properties,
height contrast in itself is sufficient for valley accentuation. As is the
case in any reflective surface, the amount of energy returned to the source
is a function of the orientation of the surface relative to the direction of
transmission (aspect angle). Thus with the aspect angle of the transmitted
energy relative to the riverain forest essentially 90° in contrast with the
aspect angle, with flat savanna (less than 45°) a brightness contrast on the
near range side (Figure 3) is assured. This is emphasized by the greater
accentuation of higher order streams when oriented normal rather than parallel
to the look direction.
Vegetation
The value of using imagery of both sensors is best emphasized in vegeta-
tion mapping. On Band 7 LANDSAT imagery, vegetation contrasts are related to
leaf mesophyll structure, including water content, and on Band 5 to visible
red reflectivity. Contrasts on radar imagery are dependent upon dielectric
properties, strongly influenced by moisture content and stem and leaf configura-
tion. In Togo, in general, a region of flat to gently rolling terrain classi-
fication of 10 distinct vegetation categories has been realized (Table 3).
Table 3
Vegetation Types Detectable on X-Band Radar Imagery
from Togo, West Africa
Semideciduous forest
Deciduous woodland
Savanna
Seasonally inundated grassland
Marshes and swamps
Cultivated vegetation:
a. Oil palms
b. Coconut palms
C.. Teak
d. Intensive mixed agriculture (corn, millet, cassava,
rice, yams, bananas, plantain, beans, and cotton)
e. Eucalyptus
O C BE C9 n9 —