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Remote sensing for resources development and environmental management
Damen, M. C. J.

portions of the alluvial fans (Figure 4).
On the SIR-A image, cultivated areas may be
identified by a network of bright lines forming
mainly rectangular (G-13), square (C-10) or
triangular (G-10) grid patterns. These radar
signatures result from the specific backscattering
behavior of forested windshelter belts which often
form so-called 'kuluns' (enclosures) to protect the
cultivated land from wind erosion. The most common
trees are fast growing poplars (Populus ssp.) The
bright image tone is primarily due to the strong
volume scattering effects of microwave energy within
the tree canopy, independent of the orientation of
shelter belts towards the radar (Figure 6). Other
backscatter components include multiple reflection of
the scattered radar signal from the trees and the
surrounding ground surface, and scattering effects at
the surface of the tree canopy. The linear
arrangement of trees along cultivated land, major
irrigation and drainage canals, roads and settlements
eventually defines the outlines of the oases.
In two areas windshelter belts are hardly dectable
(H-ll, H-12)(Figure 7C), whereas the cultivated
fields can readily be recognized by their rectangular
shape and contrasting shades of grey tones. The high
regularity and the relatively large size of the field
identifies these areas as recent development schemes,
where tree growths has not yet advanced to form
sizeable wind shelter belts.
The close relationship between the irrigation
schemes of the oases and the natural drainage network
of the Pamirs is illustrated in Figure 5. The
discharge from the glacier-fed streams during the
meltwater season contributes largely to the water
supply of the Kashgar region. The catchment of the
Gez River (D-19) is most important in terms of its
large annual water discharge. It drains the entire
Kingata Range, the northern and western flank of
Mount Kongur and defines the eastern divide of the
Sarikol Mountains. At the edge of the mountain zone
the rivers are regulated in part by the headworks of
the irrigation systems. The meltwater is diverted
into distributary canals across the alluvial fans
(E-14, G-17) and then fed into the respective
irrigation and drainage systems.
The irrigation schemes may be identified by
following the outlines of the windshelter belts,
since the course of the canals and the rows of
protecting trees are closely associated (Figure 7).
Irrigation canals of cultivated land along the foot
of an alluvial fan (G-13) tap the local ground water
horizon by a series of parallel canals. These vary
in length between 3 km and 10 km. Irrigation within
the alluvial plain relies on a distributary network
of canals, providing water either directly by the
diversion of meltwater streams or through various
water retention basins (F-ll). The entire canal
system extends more than 100 km and consists of
numerous bifurcations. A high density of shelter
belts and a high bifurcation rate of the canal system
characterize the well developed and traditional
cultivated areas (H-8). An elongated, low density
network defines more recent land reclamation areas
(F-l/2) towards the edge of the alluvial plain.
These consist of only one or two main arteries formed
by the irrigation canal, road, settlements and wind
shelter belts (Plate 2).
The surface geometry of built-up areas generally
represent dihedral corner reflectors to incident
radar beams, thus providing strong return signals and
bright image tone. Market towns such as Yengisar
(C-10) and Akto (G-13) are located in the centre of
the traditional agricultural areas. In the more
recent land reclamation areas smaller settlements may
be identified (C-6, D-7, F-3 and Plate 2).
In the western literature, there are only few remote
sensing studies which focus on regional-geographic
Plate 2. Oblique aerial view of windshelter belts in
recent land reclamation areas of western Xinjiang, as
depicted in Figure 7D. (Photo: D. Werle, Oct. 1984)
Figure 6. Schematic profile of different tracing
configurations and backscattering behavior of
incident microwave beams within or at the tree canopy
(1 = multiple scattering effects, 2 = volume scatter
effects within the tree canopy, 3 = backscatter
effects at the tree canopy).
Figure 7. Four SIR-A subscenes within the study area
representing different patterns of irrigation schemes
as outlined by strong radar backscattering behaviour
of windshelter belts along the canal and road
network. (A = traditional cultivation areas along
the foot of an alluvial fan, B = irrigation scheme
with well developed windshelter belts and harvested
fields, C = recent land reclamation area with less
well developed windshelter belts and partly
cultivated fields, D = linear development of recent
land reclamation areas within the alluvial plain).