SENSOR CHARACTERISTICS

1-3 SENSOR CHARACTERISTICS


1-33 Spectral characteristics


For each of the main missions, some specific parameters are important and have to be derived from remote sensing data. To keep the measurements as robust as possible, only wide spectral band measurements (50 nm) are considered and the objectives are to characterize the main features of plant canopies : absorption by chlorophyll, water contents and structural properties. The best and minimal set of spectral bands known to fulfill this need is composed of:

a red band centered on the absorption peak of the chlorophyll (0.665 µm),

a near infrared band corresponding to the maximum vegetation spectral reflectance and principally related to the structural properties of the canopies and to percentage of soil covered by vegetation,

a short wave infrared band centered around 1.65 µm where reflectance is related to water content of the canopy components and to its structure.

Considerations for atmospheric effects characterization or correction are added : among different possibilities that are under validation, both the use of adapted vegetation indices computed from red and near infrared reflectances and direct or indirect use of additional spectral bands in the blue region are retained. An additional band is provided in order to compute or characterise the atmospheric state (aerosols) :

a blue band (between 0.45 and 0.50 µm) where ground reflectance of vegetation cover is minimal and atmospheric aerosol diffusion effects are maximal.

The influence of atmospheric water vapor, which is most important in a wide near infrared band, is severely decreased by limiting the upper portion of the near infrared band to avoid the 0.935 µm water vapor absorption band.

The spectral responses is as “similar” as possible to the high resolution instrument bands, at least for spectral bands that participate to the same mission : the red, near infrared and short wave infrared bands.

With those considerations, the retained spectral characteristics are the following :

Spectral bands
Wavelength
BLUE
0.43 - 0.47 µm
RED
0.61 - 0.68 µm
NIR
0.78 - 0.89 µm
SWIR
1.58 - 1.75 µm

For each of the spectral bands, their spectral responses are presented on the following figure:


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