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MODIS-for-NACP 12.19.07

Reprocessed all MOD15A2GFS and MOD15A2PHN products for years 2000 through 2005 to address the following issues...

MOD15A2GFS (Gap-Filled, smoothed LAI-fPAR):

Summary:
Scaled weights can be outside range of 16 bit integer. This causes incorrect QC categories to be assigned, which can lead to misclassified high quality and low quality data.
Details:
After adjustment for second iteration TIMESAT run, small LAI values get smaller weight and high LAI values get higher weight due to up-fold weighting scheme. The weight is multiplied by 10000 and saved in short integer (16-bit) format. The highest possible weight is 4, which is out of valid range of 16-bit integer after scaling by 10000. Also, pixels with weights smaller than 0.249 are not classified due to a bug in the program. The pixels falling into these two situations are marked with original LAI values in QC layer. Therefore, both high and low quality data have a chance to slip into MODIS_LAI_FPAR_QC layer with original LAI values. Four SDS layers are affected: COMPOSED_LAI, COMPOSED_FPAR, MODIS_LAI_FPAR_QC, COMPOSED_LAI_FPAR_QC.
Solution:
1.Use a weight of 1000 instead of 10000. This avoids the highest weight out of valid range of 16-bits integer after scaling. 2.Added trap to handle pixels with an adjusted weight between 0.01 to 0.249.

MOD15A2PHE (Phenology derived from Gap-Filled, smoothed LAI-fPAR):

Summary:
Improve temporal resolution of phenology dates from 8 days to 1 day.
Details:
In previous version, the greenup (browndown) date is marked at the fitted point, which is closest to the time for which the left (right) edge has increased (decreased) to 10% of the seasonal amplitude measured from the left (right) minimum level. Therefore, the temporal resolution of the phenology dates is 8-day.
Solution:
In current version, the greenup (browndown) date is calculate as a fractional time of an 8-day period by a linear interpolation from neighbor fitted points before and after 10% of the seasonal amplitude. The interpolation parameters are calculated from the LAI value at 10% of the seasonal amplitude and the LAI values from the neighbor fitted points before and after it.

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