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Forest site in Järvselja, Estonia Summary of
ground-based LAI measurementsTiit Nilson, Tartu
Observatory
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Site location
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SPOT4 26.06.2003
Coniferous forests appear in dark, deciduous
forests in green tones, recent clear cuts and
open areas in pink and violet
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Ground-based measurements LAI-2000 and digital
hemispheric photos

• Mixed forest dominated by birch, spruce and pine
• Managed forests, some forest have been cut, so
  some changes take place from year to year
• 50-60 sample plots measured
• 3x3 km region measured in summer conditions
  2001,2002 and 2003 in leafless broadleaves
  conditions November 2003. For some plots,
  LAI-2000 measurements are available from yr 2000
• Angular distribution of gap fraction used
• Forest canopy LAI derived by Nilsons algorithm,
  uses ancillary data from the forestry database

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LAI-2000 results, average over all sample plots.
Summer conditions
   
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Comparison of LAI-2000 and hemispheric photos

• CAN_EYE and GLA programs used to process the
  photos
• A tendency to overestimate gap fraction by the
  photographic method was noted, especially for
  broadleaves
• With automatic exposition control, typically the
  crowns and branches from the upper canopy are
  over-exposed in photos and could be treated as
  sky
• After the processing of photos is finished, a new
  round of the LAI estimation is foreseen

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Agreement between LAI-2000 and photos can be
rather good, especially for conifers
A pine dominated stand
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Agreement is typically worse for broadleaves
A dense birch-dominated forest In some cases,
large differences are found
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LAI-2000 estimates on the same plots. Temporal
trajectories from year to year
Larger drops in LAI are related to
documented cuttings LAI-2000 measurement
error is quite large, partly because of
non-favorable weather conditions during
measurements
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A candidate for the transfer function Reduced
Simple Ratio (RSR). An example from an
atmospherically corrected SPOT4 image of 2 July
2002. Total LAI from ground-based LAI-2000
measurements
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RSR of two adjacent years
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Work still ongoing
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Very exotic conditions, late fall
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