An EO1-HYPERION 26 bands image of Greenland Ice shelf, July 30th 2008
EO1H0080122008212110K3 from USGS/GLOVIS

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False Color composite
EO1-HYPERION, July 30rst 2008

  • Melting has just started
  • This shallow pond is 3600 m EW
  • Water seems to be quite deep
  • Notice that the snow seems to be mostly dirty
  • The challenge is to try and achieve an optical calibration
    • how clear is the water?
    • what water type?

True color composite of raw data

Calibration diagram for bands 4, 11, 21, 26
Blue, Green, Red, Nir

Calibration diagram  for bands 2, 10, 20, 25

Optical calibration
In spite of the small size of the pond,
an excellent calibration is obtained: what it shows is threefolds
  • BPL: a consistent set of Ki/Kj ratios may be observed among all visible bands over a shallow depth range in excess of 20 meters, thus substanting the BPL assumption in an outstanding manner
  • SL: the Soils Line is clearly observed over a quite large radiance range: it is really a straight line in the plot of natural radiances, thus demonstrating very clearly how the path radiance La may be estimated, and therefore also, assuming the deep water reflectance Lsw was safely estimated, the water spectral volume reflectance Lw=Lsw-La
  • Water optics: iceshelf melt waters do not exhibit any sign of absorption by dissolved organic matter in the blue range of the solar spectrum which Jerlov's optical classification of marine waters was based upon to a large extent
    • what we seem to see is a fairly even -spectrally neutral, some would say "linear"-  increase of diffuse attenuation accross the whole visible range of the solar spectrum
    • this is distinctly the sign of an attenuation by scattering particles which adds to the spectrally contrasted attenuation by absorption of pure water
    • calling this water an O2+0.96  marine water type is definitively an abuse of Jerlov's work! Waters from melting glaciers usually exhibit that distinct slightly milky turquoise colour, definitely not the well known colour of oceanic "blue waters"

average bottom brightness
mostly very bright, but not everywhere

Maximum computed depth is ~20 m
still needs to be multiplied
by a final depth correcting factor

The hyperspectral command line

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