Raw image, true color composite

• Salar de Coipasa is located at the upper left corner of that scene

Raw image, false color composite

• This image was taken shortly after a major input of water, as the whole salar is covered with water

Bottom reflectance, true color composite

• The scene is seen "as if there was no water"
  
• The bottom of the salar is said to be lined with a layer of pink algae (Wikipedia) on which flamingoes feed.
  
• 
  
• The darkening of the bottoms is likely to be related to
  
  • river discharge, bringing nutrients and sediments
    
  • and subsequent development of a pink algal mat, high in red, low in blue
• rather thanthe effect of depth or water stratification
  

Bottom reflectance, normalized color composite

• This clearly shows that the bottoms are lined with a reddish algal mat
• Artifact: where radiances are saturated, the computed bottom signature becomes greenish instead: this is an artifact

Computed depth in decimeters

see also computed depth in centimeters

• All depths are computed using the NIR band, with 2K[nir]= ~ 4.3 m-1
• Therefore, the estimation of operational wavelengths and optical water type is of secondary importance
• Depth over saturated pixels is still acceptable, but model inversion yields a faulty greenish signature!

Calibration diagram for the full image

• Optical water type ~OII+0.6 in a high water situation
  
• Wavelengths used are 477.6, 588.5, 661.3, 834.8 nm
  
• Calibration appears to be quite reliable, in spite of the fact that the water is probably a saturated brine
  
• Depths do not seem to exceed 1.2 m
  
• Saturation: the radiances are badly saturated: this does not help!
  
• Wikipedia for Salar de Uyuni: the interpretation of this weird plot relies on the knowledge that
  
  • the bottoms are lined with a pink algal mat
    
  • the water depth in the moat hardly exceeds 1 m
    

Calibration diagram of linearized data

• This plot shows how the path radiance is tentatively specified using
  • Lsw[nir]=La[nir]
    
  • the Soil Line for all pairs of bands
    
• Once the spectral path radiance is estimated, then common sense is applied to specify the deep water radiance for all bands