Building a 1 DEM for Australia

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Building a 1 DEM for Australia
Water for a Healthy Country

• Dr David Lemon
• Research Stream Leader Water Informatics
• September 2008

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Introduction to geography of Australia
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Water scarcity A deepening problem.
8 Water Scarcity Factors
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Options for a new National DEM

• The 9 second (250 m) DEM is the only national
  bare-earth DEM
• Does not meet requirements
• ALOS PRISM/PALSAR
• 5-10m postings 3-10m Z (DTED2.5)
• Requires large investment in photogrammetry
• SPOT HRS
• 20m postings 10-15m Z (DTED2)
• COTS solution
• Requires large investment in data and
  photogrammetry for DEM
• SRTM
• DTED2 a significant improvement on DTED1
• Existing Regional DEMs and Elevation data
• Not a national coverage

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Options for the New National DEM SRTM
STRM DTED2 (1sec) offers the the most consistent
and cost-effective platform for the next National
DEM

• SRTM DTED2 (1sec) will open up the interior of
  Australia
• There is information on landscape structure never
  seen before
• Significant advancement on current 9sec DEM
• Work on 3sec SRTM has proven problematic and
  would require enormous investment in manual
  editing
• SRTM DTED2 has proven to be more suited to
  automatic artefact and vegetation removal.
• Moving from 3 second to 1 second takes us beyond
  a visually attractive product to one that is
  usable for serious quantitative purposes
• Major investment will still be required in manual
  editing and data integration
• All other options are very expensive
• Likely to be made obsolete by new data sources
  within 5 years

9sec DEM
1sec SRTM DEM
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Effects of different DEM types and resolutions
9 second
SRTM 3 second
SRTM 1 second
Regional 25 m
Lidar 5 m
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SRTM and 9 second in the arid zone
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SRTM cleanup
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Processing steps

• Fourier transform filtering to remove systematic
  stripes (sensor artifacts)
• Removal of vegetation offsets
• Identification of affected areas using vegetation
  mapping from remote sensing and direct detection
  from DEM
• Measurement of vegetation height offset and
  construction of vegetation height surface
• Removal of height offset in affected areas
• 1 second data greatly facilitates this process
• Adaptive smoothing to reduce random height
  variations in flatter areas
• Drainage enforcement with ANUDEM using mapped
  streams
• Quality assurance yet to be performed
• Manual intervention will be required in some areas

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Fourier filtering for de-striping

• This is one of the worst affected areas on all of
  Australia, but the artefact in a subtler form is
  widespread
• Not yet fully optimised some stripes remain

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Vegetation detection
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Vegetation offset removal
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Adaptive smoothing
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Drainage enforcement
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SRTM 1? contribution to catchment delineation
150 148 146 144
0 10
20 km
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Key advantages of 1 second data

• Cleanup of SRTM data is much easier and much more
  effective using the 1 second data
• 3 second data blurs the edges we need to identify
  for vegetation removal
• Released product ideally based on 1 second, not 3
  second
• Quantitative analysis demands better than 3
  second data
• Representing surface shape
• Capturing correlations with soil properties
• Matching natural and constructed features in the
  landscape

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Summary

• SRTM cleanup process is operational
• Room for improvement, development is continuing
• 1 second data provides much better basis for veg
  removal
• QA and correction will be required before release
• Currently scoping effort required
• Cleaned SRTM without drainage enforcement can
  provide a useful DEM for non-hydrological
  purposes
• Vegetation height information as a byproduct
• With appropriate stream data SRTM can construct
  the geospatial fabric for water resource
  management, in combination with other DEMs as
  necessary
• Release of SRTM 1 second data would enable a host
  of applications that are not possible with
  pre-SRTM data and have limited value using 3
  second SRTM

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Thank you
CSIRO Land and Water Dr David Lemon Research
Stream Leader Water Informatics Phone 61 2
6246 5724 Email David.Lemon_at_csiro.au Web
www.csiro.au/clw
Contact UsPhone 1300 363 400 or 61 3 9545
2176Email Enquiries_at_csiro.au Web www.csiro.au