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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 
545