This is an NDVI product automatically generated from a single satellite pass. Compared
to the composited scene, it will have more significant effects due to cloud cover. An
automatic cloud screening is used to locate the most prominent clouds.
However, there are many places where low level clouds and the edges of
the promininent clouds may fail to be detected.
Also, thin clouds which allow some of the light from the land surface to
penetrate will also go un-detected. The result is that those areas affected by
undetected clouds will have low NDVI values. Another artifact that may be
observed in the daily image is mis-registration.
The geo-location of the data is determined from parameters which describe the
motion and attitude of the spacecraft at the time of data acquisition.
Perturbations in the satellites
orbit and uncertainties in the attitude of the spacecraft can
cause the geographic location of the image data to be miscalculated.
Automated approaches based on matching the boundaries of
water badies in the scene to a reference data base have been implemented. However such
algorithms are not fool proof and errors may still be observed.