Terra
mirror side differences and striping is seen in L1B EV image data.
IMPACT TO L1B DATA SET:
It is
significant in Band 8, noticeable in Band 9, and minimal in other bands.
ESTIMATED IMPACT TO L2
SCIENCE PRODUCTS:
L2
science products have a polarization correction, so the impact will be less in
L2.
CAUSE OF EFFECT:
The
consensus is that this is primarily a polarization effect which is coupled with
the viewing geometry.
MITIGATION
APPROACH/ADDED TESTING TO CHARACTERIZE EFFECT:
MCST has
been working with the Ocean Color Group to address the improvement of the
absolute accuracy of Band 8. An analysis package describing the problem
was presented on 10/17/07. In summary, the mirror
side difference is a function of geolocation, season,
and AOI. This mirror side dependency has increased over time from
approximately 3% in 2003 to about 11% in 2007. The dependency is
indirectly included in the current RVS correction and there is no easy way to
decouple these effects. The geolocation
variation occurs too rapidy to be handled by our
Look-up Tables. Currently no polarization correction is applied in L1B
processing and it would require major code changes to the L1B algorithm to
incorporate some form of a decoupled RVS and polarization correction. One
option for dealing with this issue is to provide users with a modeled
polarization correction which they could apply to the L1B data. The
current RVS derivation for Terra uses mirror side ratio data over one specific
Ocean site. MCST is in the process of investigating the use of alternate
sites in the Terra RVS derivation.