Mapping winter fallow ground using satellite remote sensing

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Mapping winter fallow ground using satellite
remote sensing

• Heather North, Linda Lilburne, Trevor Webb,
  Stephen Burgham, Stella Belliss, David Pairman
• NorthH_at_LandcareResearch.co.nz

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Motivation

• Environmental issue nitrate leaching in
  Canterbury farmland
• Requires spatial information on winter fallow
  ground
• Location, extent and timing

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Detecting winter fallow ground
Landsat 7 imagery of mid-Canterbury, 15 June 2002
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Method

• Acquire winter sequence of satellite images
• Select image timing to capture important land
  states and transitions
• Image classification to differentiate between
  live vegetation and soil or dead vegetation
• Use two or more images to determine timing of
  transition to fallow state, and length of time in
  fallow state

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Detecting winter fallow ground
Require more than one image to determine whether
a paddock with low vegetation cover is actually
fallow

• Persistence of low vegetation cover across
  several months
• OR
• Observation of a step change from vegetated to
  non-vegetated (indicating cultivation or
  herbicide)

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Fallow rules
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Image and field data

• Image sequence in 2002 16 June, 19 August, 22
  October
• Image sequence in 2003 21 July, 18 August, 15
  September, 17 October
• Image sequence in 2004 21 May, 7 and 22 July, 24
  and 26 September
• Image sequence in 2005 starting on 30 May (we
  hope)
• Co-incident field work with as many scenes as
  possible

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Long winter fallow period
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Short winter fallow period
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Fallow 2002
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Fallow 2003
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Fallow 2002 and/or 2003
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Benefits

• Large area coverage but also paddock-level detail
• Mapping is automated, once 1-2 days fieldwork per
  image has been completed
• Inherently spatial and map-registered so easy to
  extract area measurements and locations
• Multi-year datasets can be built up to determine
  frequency of winter fallow conditions
• Will be accompanied by uncertainty information
• Combine with other map registered data, e.g.,
  with soil map to calculate fallow ground within
  each soil type.
• Other possible uses like assessing risk of wind
  erosion?

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Current status/future directions

• Currently completing development of mapping
  technique
• Discussing fallow ground maps and statistics with
  potential users
• Potential for operational use?
• Completing draft representation of associated
  uncertainty information this year
• Trialling uncertainty representation with user

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