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MODIS4NACP - MODIS Archive and Distribution System for NACP


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):

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.
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.
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):

Improve temporal resolution of phenology dates from 8 days to 1 day.
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.
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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