October 28, 2014

Inversion of biophysical variables

A Formosat time series was acquired in 2006 and 2007 at the CESBIO "South-West", located near Muret in France. On the images, Valérie Demarez (UPS/CESBIO) and Ana Feo Ortega (CESBIO) have performed a first estimate of the biophysical variable: the Leaf Area Index (LAI) which corresponds to the surface of green leaves per ground surface unit. The LAI variable is often used to model the exchanges between the vegetation and the atmosphere.

To evaluate the LAI, in situ measurements were collected (using the VALERI protocol, Demarez et al 2008) over wheat, corn, sunflower and soya plots, for three dates in 2006. These data enabled to fit a relation between the vegetation index NDVI and the LAI for the wheat. This relation seems valid for the different dates, and also gives very good results for the corn and sunflower, and at a lower extent, for the soya.


Animation LAILAI legendMagnifying Glass 

This animation shows:

  • the disjoint vegetative cycles of winter crops
    (wheat and rape) which have highs LAI from March to May,
    and summer crops (corn and sunflower),
    which have high LAI from the end of June to the end of August;

  • the LAI is very low for all the area on
    the image of June 14th: at this date, the wheat is ripe,
    while the corn barely begins to grow;

  • on the last images of this series,
    the early start, in the end of 2006,
    of wheat and rape plots.

Demarez, V. et al.,
Estimation of leaf area and clumping indexes of crops with hemispherical photographs,
Agric. Forest Meteorol. (2007), doi:10.1016/j.agrformet.2007.11.015.