Full text: Remote sensing for resources development and environmental management (Volume 1)

lergy from the 
an antenna, 
t cloud cover 
and weather 
signal film 
r returns in 
:ed to produce 
ith covers an 
'al resolution 
as in range 
geometry. 
lal from the 
of the radar 
netry and the 
ric constant, 
station cover, 
is generally 
of magnitude, 
f, i.e. image 
). 
neasure of the 
naterial upon 
Variations in 
determined by 
rock, soil or 
itions signal 
considerable 
discontinuity 
occurs. The 
, however, is 
hy and surface 
defined by the 
ation geometry 
look direction 
ge signatures. 
at an angle 
ult in radar 
t displacement 
radar antenna 
radar signal 
feature first 
irregularities 
res, and is 
ncidence angle 
IR-A) a flat 
face roughness 
e scattering, 
ngle equal and 
The resulting 
:es with an 
1.3 cm disperse 
:ering response 
the image. A 
ical relief is 
elatively high 
amount of radar backscatter is received by the radar 
antenna resulting in light grey signatures on the 
image. 
Vegetated areas appear rough and hence in bright 
tone on the SIR-A image. They are considered as 
extremely diffuse scattering surfaces due to their 
complex geometric characteristics, i.e. plant 
physionomy, but also because of their electrical 
properties. Geometrical characteristics which 
influence the radar backscatter include roughness and 
discontinuities at the plant canopy itself and within 
the volume, e.g. foliage and branches. The 
electrical properties of vegetation are a function of 
the target permittivity and conductivity, i.e. the 
dielectric constant of the biomass. 
5 IMAGE INTERPRETATION 
The SIR-A image analysis of western Xinjiang (Plate 
1) focused on the following features: physiographic 
regions, water supply, and land use patterns. A 
visual interpretation method was chosen to assess 
such image elements as tone, texture and geographical 
context. Thematic maps were produced at an original 
scale of 1:500,000 using various transparency 
overlays. Locations mentioned in the text, e.g. 
(A-7), refer to Plate 1, Figure 4 and Figure 5. 
The analysis was supported by ground observations 
made during a field trip in October 1984, by data 
extracted from topographical and geological maps 
(0NC, G-7, 1:1,000,000 and Geological Map of China, 
1:2,500,000), and by material presented in the 
literature. 
Table 1. SIR-A image interpretation chart. 
PHYSIOGRAPHIC REGIONS 
& Terrain Categories 
IMAGE 
TONE 
IMAGE 
TEXTURE 
BOUNDARY 
" RELIEF 2 ' 
Impression 
DRAINAGE 3 ' TECTONIC 
pattern/density CONTROL 
1 SANDY DESERT 
dark 
smooth 
+/- 
internal 
nona 
2 ALLUVIAL PLAIN 
medium 
fine-grain 
+/- 
parallel (1) 
moderate 
Floodplains 
dark-grey 
smooth 
+ 
braided (1) 
moderate 
Sand Dunes 
dark 
smooth 
+ 
internal 
n.a. 
3 ALLUVIAL FANS 
medium 
fine 
+ 
distrib. (m) 
none 
Floodplains 
light-grey 
fine-grain 
+ 
-- 
distrib. (h) 
none 
Old Terraces 
dark 
smooth 
+ + 
+ 
parallel (m) 
none 
4 DENUD. MOUNTAIN 
& HILL REGION 
medium/ 
light-grey 
fine 
+ 
+ 
dendritic/ 
parallel (h) 
high 
5 EROSIONAL HIGH 
MOUNTAIN REGION 
dark-grey/ 
light-grey 
coarse 
+ 
+ + 
sub-parallel/ 
dendritic (m) 
moderate 
6 NIVAL-ALPINE 
REGION 
dark/light 
coarse 
+ + 
+ + 
sub-parallel/ 
dendritic (1) 
moderate 
Snovfields 
light 
fine-grain 
- 
- 
n.a. 
n.a. 
Glaciers 
med./light fine-grain 
+ 
+/- 
n.a. 
n.a. 
''Boundary: 
+ + ■ very sharp 
^Relief Impression: 
+ + ■ very good 
¿ \ 
^Drainage density: 
h - high 
m “ medium 
— - ■ transitional - - - none 
n.a. - not applicable 
5.1 Physiographic Regions 
On the SIR-A image a number of terrain categories and 
various sub-categories may be recognized (Table 1) 
and grouped into six major natural physiographic 
regions (Figure 4). These regions are oriented in a 
SW-NE direction. A distinct boundary divides the 
moderately to highly reliefed uplands of the Pamirs 
and the lowlands of the Tarim Basin. 
A uniform dark tone and a smooth texture in the SE 
part of the study area characterize the sandy desert 
as a marginal part of the Taklimakan Desert. Dune 
formation or drainage channels can not be identified, 
indicating that the incident radar energy is largely 
absorbed by a continuous cover of loose, dry sand. 
As a result the backscatter signal is very low. The 
ragged boundary towards the alluvial plain is 
partially transitional. 
Medium grey tones and a fine granular texture are 
the dominant image characteristics of the alluvial 
plain. Clay, silt and loess deposits which are in 
part deformed by wind erosion contribute to moderate 
radar backscattering. Low density and sub-parallel 
drainage channel sections appear as irregular dark 
and dark-grey bands (H-10). During the dry season 
most of the active river channels do not contain 
water. Their fine-grain sediments and smooth surface 
morphology produce low backscatter signals. Sporadic 
alignments of light grey tone and crescent shapes 
(F-6/7) delineate cliffs of fluvial terraces which 
act as corner reflectors when oriented towards the 
radar. The drainage network in the alluvial plain is 
generally oriented in a E to ESE direction. Small 
elongated streaks of dark-grey tone mark the present 
position of various groups of sand dunes (D-4). The 
dunes are almost exclusively oriented in a SE 
direction which corresponds well with the prevailing 
regional wind direction. The most outstanding 
features within this alluvial plain are linear and 
rectangualar outlines of the oases. These are dealt 
with in a seperate section. 
Along the base of the Pamirs various shades of grey 
tone as well as smooth and fine-grain image texture 
suggest different radar backscatter intensities 
within a zone of interlocked alluvial fans. Their 
individual delta-shaped outlines and the distributary 
pattern of the drainage channels are the principal 
recognition elements on the SIR-A image. 
Medium-grey, dark-grey and dark tones allow for 
further subdivision into active channels (G-14), 
Pleistocene fan deposits (E-13), and older eroded 
fluvial and/or fluvio-glacial sediments (1-21), 
respectively. The different grey tone levels 
probably account for progressive accumulation of 
aeolian sand or loess deposits on the geneally coarse 
gravel fans. At the funnel-shaped head of the fans, 
Quaternary fluvial and fluvio-glacial terraces are 
frequently undercut by stream erosion during the 
meltwater season (F-18). The two largest fans within 
the study area extend over an area of 360 km 2 (F-14) 
and 380 km 2 (H-16). Gravel bodies such as these have 
an excellent water storage capacity. The allocation 
of oases along the foot of the alluvial fans is a 
clear indicator of the present ground water horizon. 
The denudational mountain and hill region 
represents terrain which is highly dissected by a 
sub-parallel and sub-dendritic drainage pattern. 
Numerous small valley sections are oriented toward 
the radar and produce an overall light-grey tone and 
a fine image texture. Partial coverage of aeolian 
sediments and the low resistance of the underlying 
material result in intensive erosion and high density 
drainage (D-17/18). Tracts of elongated ridges 
represent more resistant lithologic units (F-17) or 
hint at folded sedimentary rock structures (B-15). 
Various linear and partly angular features between 
this upland area and the lowlands indicate a high 
degree of tectonic control by a major NW oriented 
boundary fault (A-14/ H-21) which suffered lateral 
displacement (G-19). 
In the erosional high mountain region, topographic 
relief is expressed in light grey tone where slopes 
are facing the radar look direction. Slopes oriented 
away from the sensor appear dark. The moderate to 
coarse image texture is a function of drainage 
density which in turn reflects a higher resistance of 
lithology to erosion compared to the previous region. 
Crestlines of ridges are irregular and sharp in the 
eastern portion of the mountain area (G-22/23), 
whereas higher uniformity charcterizes the Sarikol 
Mountains (D-28). Accumulation of Pleistocene 
fluvial and fluvio-glacial sediments occurs in a 
major NNW oriented intermontane basin (D-26). Its 
partly dissected terrain has low relief, giving 
smooth image texture and dark grey tone against which 
the dark outlines of a lake (D-26/27) barely 
contrast. Recent floodplains (C-26) appear in 
lighter tones and a fine granular texture. The NW 
extension of this tectonically controlled basin, or 
graben system, suffered lateral displacement in the
	        
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