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Forest site in J ä rvselja, Estonia: Summary of ground-based LAI measurements Tiit Nilson, Tartu Observatory. Site location. SPOT4 26.06.2003. Coniferous forests appear in dark, deciduous forests in green tones, recent clear cuts and open areas in pink and violet. - PowerPoint PPT Presentation
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Forest site in Järvselja, Estonia: Summary of ground-based LAI
measurements
Tiit Nilson, Tartu Observatory
Site location
SPOT4
26.06.2003 Coniferous forests appear in dark, deciduous forests in green tones, recent clear cuts and open areas in pink and violet
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 Nilson’s algorithm,
uses ancillary data from the forestry database
LAI-2000 results, average over all sample plots. Summer conditions
LAI tree storey LAI ground
LAI total
Year Nilson’s algorithm
Forestry database
LAI-2000
LAI-2000
2001
3.24
3.71 0.84 4.12
2002
3.54
3.56 0.86 4.40
2003
3.62
3.54
0.80
4.43
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
Agreement between LAI-2000 and photos can be rather good,
especially for conifersJarvselja 75-02, 2002 summer
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0 10 20 30 40 50 60 70 80 90
View Zenith Angle, Degrees
Gap
Fra
ctio
n
LAI-2000
CAN_EYE
GLA
A pine dominated stand
Agreement is typically worse for broadleaves
A dense birch-dominatedforest
In some cases, large differences are found
111_04
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 20 40 60 80
View zenith angle, degrees
Ga
p f
rac
tio
n CAN_EYE 02
CAN_EYE 03
LAI-2000 02
LAI-2000 03
LAI-2000 estimates on the same plots. Temporal trajectories from year to year
0
1
2
3
4
5
6
7
8
9
2000 2001 2002 2003 2004
Year
Can
op
y_L
AI
160-04159-04161-05162-07104-17134-01106-12107-13111-0479-16141-06111-11186-08186-07164-04165-02137-0875-0276-04188-07188-09166-06167-07134-07137-03108-07108-08137-06136-05136-07
=
Larger drops in LAIare related to documentedcuttings
LAI-2000 measurement error is quite large, partly because of non-favorableweather conditions during measurements
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
2002 y = 0.6215x - 0.6094
R2 = 0.5146
0
1
2
3
4
5
6
7
8
9
2 4 6 8 10 12
Reduced Simple Ratio (RSR)
LA
I to
tal
RSR of two
adjacent years
Jarvselja, SPOT 2001&2002
y = 1.1071x + 1.355
R2 = 0.8402
0
2
4
6
8
10
12
0 2 4 6 8 10
RSR 2001
RS
R 2
002
Work still ongoing
Very exotic conditions, late fall