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Airborne Spectrométrie Acquisition 
(AVIRIS. ISM,.,.) 
Laboratory Analyses 
Figure 1 : Schematic presentation of the methodology (Gastellu-Etchegorry et al., 1993). 
EL Experimental data 
IL1 Study area 
The Landes study area is a large, flat homogeneous forest of one million hectares, producing 20% of French 
timber, mainly maritime pine (Pinus pinaster). The test area encompasses several thousand hectares that 
comprise 49 large forest stands (mean area of 20ha), rectangular in shape and delimited by Fire protection 
tracks or large access tracks. Characteristics (i.e. row spacing and width, tree density, dbh, canopy depth, 
understory vegetation,...) of the stands of maritime pine are well documented (Beaudoin et al., 1993). This 
information was checked, and up-dated wherever necessary. As The Landes test site represents an ideal 
prototype of managed forest ecosystem over a large chronosequence of the maritime pine, it is particularly 
appropriate for ( 1 ) the study of sensitivity of high resolution reflectance spectra to forest characteristics such as 
age of trees, biomass, lignin content,.., and ( 2 ) the development and testing of simulation models. 
A radio-sonde exploration was completed at the time of AVIRIS measurements, for determining atmospheric 
pressure, temperature, and humidity profiles. Simultaneously, a 21km visibility was measured in the field. 
II .2 Spectrometric airborne measurements 
AVIRIS (Airborne Visible / Infrared Imaging Spectrometer) and ISM (Infrared Spectrometer) data were 
acquired in June 1991 during the Mac Europe campaign of NASA/JPL over The Landes test site. The ISM 
instrument is a spectrometer with 64 contiguous 12.5nm wide spectral bands in the [0.8pm 1.5pm] region and 
64 contiguous bands 25nm wide in the [1.6pm 3.2pm] region (Figure 2). IFOV is 1'. Solar spectrum is 
acquired on board, and an on-board camera records information in the visible region for further identification 
of targets (Zagolski et al., 1992). Due to calibration problems, our work was essentially based on AVIRIS data. 
AVIRIS data consist of 210 contiguous lOnm wide spectral bands in the [0.4pm-2.45pm] region. The 
instantaneous field of view is lmrad. Six images (512 rows x 614 columns) were acquired through a 19,600m 
altitude flight; i.e. 11km swath width at a ground pixel size of 20m. Due to instrumental problems spectral 
bands larger than 2270nm were particularly noisy. This effect was minimized while considering only 
radiometric averages over the pine parcels. 
Atmospheric effects were analysed because they modify middle infrared (MIR) reflectances and strongly 
influence visible (VIS) and near infrared (NIR) reflectances that are used for retrieving essential parameters 
such as the Leaf Area Index (LAI), w'hich is used for computing foliar MIR reflectances through canopy 
reflectance model inversion.