Reflectance Spectra

Reflectance spectra for 5 surface materials.

For vegetation and water, note the huge difference betweenthe red and NIR bands.

  • Vegetation: low reflectance in the visible, but some reflectance in the green, and then strong reflectance in the NIR
  • Water: low reflectance in the visible, but no reflectance in the NIR. 
Normalized ratios can be used to differentiate surface materials. For instance, the NDVI takes the difference between red and NIR bands (3 and 4 for Landsat 7, 4 and 5 for Landsat 8) over their sum. Vegetation will be low in the red band 3 and high in the NIR band,  leading to a very large value of the ratio. Non vegetation, like soil or rock in the spectra above, will have very similar values in red and NIR and hence a low NDVI ratio.

Ratios can deal with different total illumination resulting from different solar elevations and partial shading.

 

With enough detail in the spectra, note that different kinds of vegetation can be discriminated.

Reflectance spectra, available in ASCII format (ASC extension) from USGS Spectroscopy Lab (version 6a), should be placed in a x:\mapdata\spectral_library directory.  They can be plotted from

References.


Last revision 1/17/2018