Reduced simple ratio better than NDVI for estimating LAI in Finnish pine and spruce stands

Pauline Stenberg*, Miina Rautiainen, Terhikki Manninen, Pekka Voipio, Heikki Smolander

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

111 Citations (Scopus)

Abstract

Estimation of leaf area index (LAI) using spectral vegetation indices (SVIs) was studied based on data from 683 plots on two Scots pine and Norway spruce dominated sites in Finland. The SVIs studied included the normalised difference vegetation index (NDVI), the simple ratio (SR), and the reduced simple ratio (RSR), and were calculated from Landsat ETM images of the two sites. Regular grids of size 1 km2 with gridpoints placed at 50 m intervals were established at the sites and measurements of LAI using the LAI-2000 instrument were taken at the gridpoints. SVI-LAI relationships were examined at plot scale, where the plots were defined as circular areas of radius 70 m around each gridpoint. Plotwise mean LAI was computed as a weighted average of LAI readings taken around the gridpoints belonging to the plot Mean LAI for the plots ranged from 0.36 to 3.72 (hemisurface area). All of the studied SVIs showed fair positive correlation with LAI but RSR responded more dynamically to LAI than did SR or NDVI. Especially NDVI showed poor sensitivity to changes in LAI. RSR explained 63% of the variation in LAI when all plots were included (n = 683) and the coefficient of determination rose to 75% when data was restricted to homogeneous plots (n = 381). Maps of estimated LAI using RSR showed good agreement with maps of measured LAI for the two sites.

Original languageEnglish
Pages (from-to)3-14
Number of pages12
JournalSilva Fennica
Volume38
Issue number1
Publication statusPublished - 2004
MoE publication typeA1 Journal article-refereed

Keywords

  • Boreal coniferous forests
  • Landsat ETM
  • Leaf Area Index
  • Spectral vegetation indices

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