The aim of this study was to test the potential of MODIS NDVI 
data as long-term tracer of wetland vegetation in the DSC. 
Particular objectives were to identify and map the spring 
vegetation greenness, to produce and analyse time traces of 
NDVI and wetness indices, as well as to relate information 
about temporal variability of springs derived from medium 
resolution remote sensing to groundwater flow, rainfall, 
ecological processes and human management 
2. METHODS 
MODIS-Aqua NDVI images centred on DSC were acquired 
between July 2002 and May 2010, providing continuous 16-day 
composite data over approximately 8 years. MODIS data were 
resampled to WGS 84 / UTM zone 53 and maps of the study 
area were produced (Figure 1c). With reference to air photos, 
field observation and site-specific knowledge (White and Lewis, 
2010a, b), 21 MODIS pixels representative of six different 
typical vegetation and land cover types at DSC were 
geographically located on the MODIS-Aqua images. Four of 
these pixels were representative of Melaleuca glomerata, three 
of Phragmites australis, and two of ephemeral vegetation. For 
comparison, four pixels representatives of saline, three of 
upland and five of riverine cover types were also selected. 
These ecosystems are the typical non-wetland ecosystems 
encountered around the DSC (figure 1a). 
Time-traces of NDVI were extracted from these pixels and 
analysed with a Non-Metric Multidimensional Scaling (NMDS) 
ordination to determine whether the wetland types could be 
differentiated on the basis of the NDVI sequence, and if so, to 
identify the NDVI factors contributing to the separation. The 
90" percentile (P90) of the NDVI datasets were calculated in 
  
  
  
    
   
    
   
  
      
  
    
   
  
  
    
     
  
    
   
  
  
  
  
    
   
  
  
  
  
     
   
  
  
  
   
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
order to determine a NDVI threshold value discriminating 
photosynthetic activity of the characteristic wetland vegetation 
species in the Dalhousie Springs from surrounding land 
responses. Mean Monthly NDVI time traces were also 
computed from the distinctive Melaleuca glomerata, 
Phragmites australis and ephemeral vegetation NDVI values 
recorded between 2002 and 2010. 
In order to study the extent (in km?) of the vegetated wetland 
area in the Dalhousie Springs Complex, the number of pixels 
with NDVI values over the selected threshold was computed 
and converted to area (Areaypy;, km?) of vegetated wetland for 
each of the 16-day composite MODIS-Aqua images. 
Complementary MODIS-Terra NDVI images between February 
2000 and July 2002 were also processed to extend the period of 
wetland area recording. 
The intra and inter-annual patterns of the Areaypy; index were 
then related to the seasonal wetland vegetation changes, as well 
as to rainfall (mm) and groundwater flow discharge (L.s™) data 
furnished respectively by the Australian Government Bureau of 
Meteorology and the South Australian Department of 
Environment and Natural Resources. As flow gauge data are 
sparse and not available for the whole Dalhousie Springs, 
comparisons between the vegetated wetland area and the 
groundflow data were conducted at a large spring (DAAOI) 
within DSC where flows were recorded between 2002 and 2010 
(Figure 1c). Furthermore, as flow measurements are not 
available regularly at this spring (1 or 2 measures/year), 
comparison of mean annual discharge data and Areanpy, Were 
performed. (Figure 1c, DAAO0O1). Finally, rainfall 
measurements were selected from the Hamilton Station, the 
closest meteorologic station to Dalhousie (~80 km west). 
23 ken 
  
  
30km 
Figure 1: a) Extent of the Great Artesian Basin in Australia and location of the Dalhousie Spring Complex. b) Location of selected 
pixels: Dalhousie Spring vegetation (P: Phragmites; M: Melaleuca; E: Ephemeral) and surrounding lands (S: Saline; U: Upland; R: 
Riverine). c) Example of MODIS NDVI map. Spring discharge boundaries for the whole DSC and the spring DAAO001 are indicated 
by blue and red lines, respectively. Boundaries are from White and Lewis (2011). 
  
   
Intern: 
Figur 
cal 
calcul 
3.1 De 
Figure 
distance 
2010) € 
feature 
represe 
The ve 
differer 
covers 
wetlanc 
system 
values 
Surroui 
NDVI 
sites (P 
On the 
establi: 
indicat 
pixels 
Was ap 
Dalhoi 
lc) anc 
32 T 
Figure 
areas 
Comp: 
to con 
from t