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Up Topic Frequently Asked Questions / Data Products & Algorithms FAQ / How does Sun glint affect ocean color data processing? (locked)
- By Donna Date 2005-06-08 09:59 Edited 2006-05-16 11:17
What is Sun glint and how does it affect ocean color data processing?

Sun glint appears as a white strip in the Level 1 (true color) imagery.  It is
the specular reflection of sunlight off the sea surface. It's signal is so much
greater than the sunlight reflected from below the surface that retrieval of
information about in-water constituents by direct measurement is severely
compromised, often impossible.  The algorithms used to process ocean color data
make use of ancillary data on surface winds in conjunction with the sun/sensor
viewing geometry to determine where glint is most likely to contaminate the
ocean color signal.

In regions where there is a low to moderate glint signal, it is possible to
estimate the contribution of sun glint to the total signal. With such an estimate
we can remove the glint signal, allowing Level 2 processing to proceed.  The
current Level 2 processing code does this, as described in Wang and Bailey (2001). 
Such a correction is not practical for highly glint contaminated regions.

Some inferences about the state of the water column may be possible by noting
that organic films [produced by some phytoplankton, leaked by water craft,
etc.] can modify the sea surface roughness which in turn changes the level of
glint seen by the sensor. 

Why does sun glint affect MODIS more than SeaWiFS?

Since MODIS does not tilt to avoid looking into the sun glint field, therefore
its glint affected areas tend to be considerably larger than for those sensors
which do tilt such as SeaWiFS. Note that the glint affected region in Aqua
MODIS images is slightly to the west of the swath's center line. This is
because Aqua crosses the equator in the early afternoon when the sun is a bit
west of the sensor. MODIS on Terra has its glint region to the east of the
center line because Terra crosses the equator in the late morning when the sun
is a bit to the east of the sensor.
Up Topic Frequently Asked Questions / Data Products & Algorithms FAQ / How does Sun glint affect ocean color data processing? (locked)

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