|Current (preliminary) form of the PSF of band 16, detector 1||Increase of captured signal with window size|
The MODIS PSF will result in stray light contamination from adjacent pixels. The largest impact is to low radiance ocean observations which are within a few kilometers of bright sources such as clouds, coastlines, or sun glitter. Until a correction can be developed, the near-term solution which is proposed for this reprocessing is to simply mask all observations within a few pixels of any cloud or saturation-flagged pixels. The model estimates of the point-spread function for MODIS suggest that the majority of the contamination can be eliminated with a 7x5-pixel masking (+/-3 pixels along scan, +/-2 pixels along track) around these high-radiance pixels. This represents a considerable data loss at Level-2, but confidence in the remaining data is substantially enhanced.
A direct impact of this additional masking can be seen in the global deep-water aerosol optical thickness (AOT) comparisons with SeaWiFS. The straylight masking brings MODIS mean AOT retrievals down by more than 50%, and the results are now in good agreement with SeaWiFS. Note that the standard SeaWiFS processing already includes masking and correction for straylight contamination.
|before straylight masking||after straylight masking|
Last updated 19 January 2005, B. Franz & G. Meister