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

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Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Classification of the Riverina Forests of south east Australia
using co-registered Landsat MSS and SIR-B radar data
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A.K.Skidmore, P.W.Woodgate & J.A.Richards
Centre for Remote Sensing, University of New South Wales, Kensington, Australia
Abstract: The Riverina forests of south east Australia have been extensively managed for 150 years as a
productive source of railway sleepers and sawn timber. This study was the first Australian forestry
application to evaluate the use of SIR-B radar (co-registered with Landsat MSS data) for mapping forest types
and site quality classes. The techniques used for radar speckle reduction, registration of images and
classification or cover classes are discussed. Results show that the classification accuracy was superior
when the two data sources were used in combination rather than individually.
1. Introduction
The objective of the study was to map forest types and site
qualities of the Riverina forests using SIR-B imagery as a data
source by itself and in combination with Landsat MSS data.
The study area straddles the Murray River, which is the bordei
between the States of New South Wales and Victoria in Australia
(see Figure 1).
Figure 1 - Location of the study area
About 15,000 years ago, a 10m high fault line developed in a
north-south direction across the course of the Murray River,
effectively damming the river and causing the river to diverge into
two arms, to the north and south. The huge triangular sedimentary
delta that formed was subject to periodic flood inundation caused by
the high winter/spring precipitation in the headwaters of the Murray
River. This flood plain is now dominated by virtually pure
monospecific stands of River Red Gum (Eucalyptus camaldulensis),
due to this species' unique ability to withstand periodic flooding, in
lower lying areas of the delta, shallow lakes and swamps are in
various stages of silting up. Aeolian sand hills rise up to 12m above
the flood plain and support tree species including Yellow Box
(Eucalyptus melliodora) and Grey Box (Eucalyptus microcarpa).
However, local variation in topography is generally less than 2m, anc
shadowing effects can be considered minimal or non-existant.
Interestingly, at the time of the SIR-B overpass, the forest complex
was experiencing an 80% flood of the total forest area. The Landsat
image was recorded about a month later when the flood had just
Three site quality classes have been defined for River Red Gum
stands (Table 1). Site quality is the actual (or potential maximum
average) height of trees in a forest stand, and is also an indication o
the stand density. Stand density is a measure of stand basal area (i.e
cross sectional area of tree stems at 1.3m per unit area) or stocking
Table 1 also details the other major cover types in the study area.
This present forest structure has been modified by man's
activities. The Aboriginal population regularly burnt the forest to
maintain an open woodland condition of veteran trees, which
enhanced the value of the forest for hunting. From the 1840's,
European man used the forest for grazing runs and for timber. Curren
logging is on a selection basis, with some overmature trees being
removed during logging to improve regeneration. Stands are
uneven-aged and very variable in tree size and distribution as a
result of this history. However, stand density (basal area or
stocking) is correlated to site quality (see Table 1), with red gum
(site quality 1) being the densest forest.
The study area was selected because the Centre for Remote
Sensing at the University of New South Wales had acquired a clear
Table 1 - Major cover types in thè Riverina Forests
Land cover Typical location of
type occurence
Definition and description of
land cover type
River Red
Gum Site
Quality 1
Frequently flooded e.g.
river bends. Areas
with good access to
subterranean water.
Dominant tree height (or pot-
ential tree height) of 31-45 m.
Higher stand density (70
m^/ha).Heavily stocked regen
eration. Ground cover of leaf
litter or grass.
River Red
Gum Site
Quality 2
Intermediate levels of
the floodplain. Depth to
watertable 6-9 m.
Dominant heights of 21-31 m.
Increasing number of woody
understorey plants. Moderate
stand density.
River Red
Gum Site
Quality 3
Higher levels of flood-
plain. Depth to water-
table > 9 m. Infrequent
floods of short duration
Poor stand development. Open
savannah woodland of <21 m in
height. Woody understorey
species more pronounced.
and Grey
Irregularly flooded and
flood-free areas
Stands vary in dominant height
from 6-30 m. Grass component
in understorey.
and Giant
Watercourse and
semipermanent swamps
Tussock grass formation of
2-3 m.
SIR-B radar image of the Riverina forests from the flight of Space
Shuttle Challenger in October 1984. Comprehensive forest type and
site quality maps already existed for the area, and were made
available by the Forestry Commission of N.S.W. and the Department o
Conservation, Forests and Lands of Victoria. A unique opportunity
thus occured to generate forest type maps using SIR-B imaging rada
combined with Landsat MSS data of approximately the same dates.
Details of the Landsat MSS and SIR-B radar are described in Table 2.
Table 2 - Description of the Landsat MSS and Sir-B radar
Landsat MSS
SlR-B Radar
Space Shuttle
Acquisition date
17 November 1984
13 October 1984
Acquisition time
Pixel resolution
79 x 56 m
12.5 m
5 x 10-5 cm -
1.1 x 10-5 cm
23.5 cm
Incidence angle
32.7 - 39.3 degrees
Two obstacles had to be overcome to meet the objectives of
the study. The first was radar speckle, which is an unavoidable
product of the illumination of a surface by coherent monochromatic
radiation. Despite the fact that SIR-B imagery was produced by
averaging four independent looks, further speckle reduction was
necessary prior to classification to prevent aberrant speckled pixels
from causing misclassification. Secondly, spatial resolution