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

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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

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View zenith angle, degrees

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p f

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CAN_EYE 03

LAI-2000 02

LAI-2000 03

LAI-2000 estimates on the same plots. Temporal trajectories from year to year

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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

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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

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RSR 2001

RS

R 2

002

Work still ongoing

Very exotic conditions, late fall