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(5) Develop routine operational procedures for the
ongoing monitoring of wetlands and tropical
savanna woodlands in Northern Australia.
(6) Continue and extend the modelling of radar
backscatter characteristics of Australian tree
types.
THE STUDY AREAS
A Northern Australia
The area chosen for investigation is referred to as the ‘top
end’ of the Australian continent and includes north-
eastern Queensland, the Northern Territory and north-west
Western Australia.
Scasonally and intermittently inundated floodplains occur
along most of the coastal draining rivers of the ‘top end‘
(Finlayson et al, 1991). Common to this monsoon-
influenced coastal region is a dry season from April to
November and a wet season from December to March.
Although considerable variation in the onset and duration
of rainfall occurs across the region, total precipitation
declines from north to south along both the western and
castern coastlines of the Australian continent.
While the individual stream systems draining to the north-
west, north and north-east of the continent are smaller
than many of their counterparts in southern Australia,
together these river systems account for approximately
two-thirds of the total continental run-off (ARWRC,
1976).
In most of these catchments which drain from an upland
escarpment and interior plateau towards the coast, stream
flow is seasonal but prolonged throughout the dry season,
especially in the lower reaches by reverse drainage from
floodplains, lakes, billabongs and waterholes with water
stored from the wet season. Collectively these systems
which retain and then release water or which are
permanently flooded after the wet season are referred to
as freshwater wetlands as opposed to the saltwater and
tidal wetlands of the coastal littoral.
The ecosystems developed in these floodplain
environments are complex, dynamic and resilient, often
undergoing annual changes in water depth ranging from
being completely dry to being covered for 3-4 months by
2-3m of water. Vegetation communities present include
forests, woodlands, scrub and heath, shrublands, sedge
and grasslands and extensive macrophytic floating and
submerged herblands, all of which relate and respond to
the hydrologic regimes of either permanent or seasonal
inundation.
In addition to plants, these freshwater wetlands are
important breeding grounds and refuges for micro- and
macroscopic animal species (Finlayson op cit).
While many freshwater wetlands in Northern Australia
have been relatively undisturbed by human activities in
the past, increasingly they are coming under threat from
International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
saltwater intrusion, invasion by exotic weeds, degradation
by feral animals, increased pollution from agriculture and
pastoralism and from the effects of tourism and recreation
use.
To date there is no regional map showing the distribution
and extent of wetland environments in Northern Australia.
Also, there is an absence of data to indicate the
proportion of the coastal lowland areas which remain
flooded all year round as opposed to the proportion which
dry out. Determining the spatial pattern of wetlands and
the sequence of floodplain draining and drying out is an
important first step to investigating the hydrologic,
geomorphic and ecological processes operating in these
ecosystems.
B. : ro eed o
For the potential of SAR in the study of wetlands to be
realised, careful examination of radar backscattering from
ecologically important and representative wetlands needs
to be undertaken. To facilitate this, the Alligator River
region located in the Northern Territory has been chosen
as the major laboratory site to examine the detailed
relationships between backscatter, inundation cycles and
wetland environments.
The region comprises the catchments of the East
Alligator, South Alligator and West Alligator Rivers
which contain approximately 195,000 ha of freshwater
floodplains. Over 225 plant species have been found on
the floodplain with their presence and distribution varying
annually with water depth and period of inundation being
key determining factors (Finlayson 1993).
This region has been chosen for three reasons:
. the conservation importance of wetlands found in
the Alligator Rivers region has been recognised
with the listing of Kakadu National Park which falls
within the region as a World Heritage Area on the
basis of the natural heritage value of its freshwater
wetlands and floristic diversity;
. this is one of the few sites in Northern Australia that
has ongoing research programs in aquatic biology,
plant biology and physiology, environmental
chemistry and geomorphology;
° complementary data sets covering the region,
including ERS-1, JERS-1, SIR-C/XSAR; AIRSAR;
TM and SPOT, are already available.
METHODOLOGY OVERVIEW
RADARSAT data has been acquired monthly from late
1997 and is currently being analysed.
The investigation has been broken down into a number of
sequential stages and sub-projects as follows.
L Regional mapping of wetland areas in Northem
Australia will be achieved by using RADARSAT
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