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This image depicts the 2010 Terra MODIS 1-km annual Net Primary Productivity (in Kg C/m2) over the H08/V05 tile that covers much of the western/southwestern US.
Net Primary Productivity (NPP) defines the rate at which all plants in an ecosystem produce net useful chemical energy. In other words, NPP is equal to the difference between the rate at which plants in an ecosystem produce useful chemical energy (or GPP), and the rate at which they expend some of that energy for respiration.
The version-55 of the NPP product is produced by the Numerical Terradynamic Simulation Group (NTSG)/University of Montana (UMT). It corrects the problem with cloud-contaminated MODIS LAI-FPAR inputs to the MOD17 algorithm. The original, uncorrected datasets constitute the version-4 NPP products. For further details regarding the differences between the NTSG and NASA versions of this product, please consult the document referenced in the following news release: Terra MODIS GPP/NPP Products from NTSG/University of Montana
Version-55 Terra/MODIS NPP products are validated to Stage-3; this means that its accuracy was assessed and uncertainties in the product were well-established via independent measurements made in a systematic and statistically robust way that represents global conditions. These data are deemed ready for use in science applications.
See Product Description
|HDF Science Data Sets||UNITS||BIT TYPE||FILL||VALID RANGE||SCALE FACTOR|
|Gridded 1 Km Annual Gross Primary Productivity||kg_C/m2||16-bit signed integer||0 – 65500||0–65500||0.0001|
|Gridded 1 Km Annual Net Primary Productivity||kg_C/m2||16-bit signed integer||65530–65535||0–65500||0.0001|
|Gpp_Npp_QC_1km||Percent||8-bit unsigned integer||255–250||0–100||NA|
Table 1: Terra/MODIS Net Primary Production Yearly L4 Global 1km product’s HDF Science Data Sets
|65535||Fill value: conventional HDF-EOS fill value assigned to non-modeled pixels not falling into other categories below|
|65534||Perennial salt or inland fresh water body cover type|
|65533||Barren, sparsely vegetated (rock, tundra, desert) cover type|
|65532||Perennial snow or ice cover type|
|65531||Permanent wetlands/inundated marshland type|
|65530||Urban/built-up cover type|
Table 2: Fill Values for Annual GPP and Annual NPP
Interpreting the Gpp_Npp_QC_1km SDS
The improved, yearly MODIS GPP/NPP product does not use QA bit-fields but a meaningful number. This number refers to the percentage of filled MOD15 LAI caused by cloud-contamination during a growing season (defined when daily minimum air temperatures are above –8 Celsius) in a year. Therefore, the valid annual QA values range from 0 to 100; a high value refers to a high frequency of cloud-contamination. For example, QA is high for tropical rainforests but low in arid areas. The QC fill values' descriptions (255 – 250) correspond to the different non-vegetated land cover types identified in Table 2 above. For instance, 255 corresponds to the description for 65535, 254 to 65534, 253 to 65533, etc.
Algorithm Theoretical Basis Document
Accuracy and Validation Status
|Temporal Coverage:||January 1, 2000 - December 31, 2010|
|Area||~10 x 10 lat/long|
|File Size||~7 MB|
|Dimensions||1200 x 1200 rows/columns|
|Science Data Sets (SDS HDF Layers)||3|
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