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1155AI-GEOSTATS: LAI (leaf area index) fromNDVI

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  • rocchini@unisi.it
    Aug 12, 2003
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      I'd like to know if the approach I used to derive LAI from NDVI is correct.
      STEP 1: I've got 46 field point values of LAI (leaf area index, namely the
      cover of plant leafs)
      STEP 2: I derived the NDVI index from a multispectral image.
      STEP 3: For every field plot I calculated the mean NDVI of 3x3 neighbour
      STEP 4: I made a regression between mean_NDVI and LAI.
      STEP 5: r^2 was low (0.34), r being 0.70, but t, measured as
      r/sqr((1-r^2)/(n-2)) was over the minimum t 2.7, being my t 5.75
      STEP 6: Since the correlation was highly significant p<0.01 I applied the
      equation of the regression line y= 4.9053x + 0.2406 where y was LAI and x
      was NDVI to the NDVI map, obtaining the LAI map
      STEP 7: I made a control on the accuracy of the model by measuring the mbe
      (mean bias error) calculated as the mean of single errors for every plot
      (46 measures): mean of P-O
      where P was the estimated LAI value and O the observed, by obtaining a mbe
      of 0.03249587

      1. Could I apply the equation as in step 6?
      2. Could I control my model by using the same input observed values as in
      step 7?


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