The Moderate Resolution Imaging Spectroradiometer (MODIS) Net Primary Productivity (NPP) product (MOD17A3) 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 Gross Primary Productivity (GPP), and the rate at which they expend some of that energy for respiration.
Version 5.5 of the NPP product is produced by the Numerical Terradynamic Simulation Group (NTSG) at the University of Montana (UMT). It corrects the problem with cloud-contaminated MODIS Leaf Area Index (LAI)/Fraction of Photosynthetically Active Radiation (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 5.5 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.
The following data citation is recommended when using MOD17A3 data: Running, S., Mu, Q., Zhao, M. (2011). MOD17A3 MODIS/Terra Net Primary Production Yearly L4 Global 1km SIN Grid V055 [Data set]. NASA EOSDIS Land Processes DAAC.
|File Size||~7 MB|
|Temporal Extent||2000-01-01 to 2014-12-31|
|Geographic Dimensions||1200 km x 1200 km|
|Number of Science Dataset (SDS) Layers||3|
|Pixel Size||1000 m|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor|
|Gpp_1km||Gridded 1 km Annual Gross Primary Productivity||kg C/m²||16-bit unsigned integer||65529 to 65535||N/A||0 to 65500||0.0001||Npp_1km||Gridded 1 km Annual Net Primary Productivity||kg C/m²||16-bit unsigned integer||65529 to 65535||N/A||0 to 65500||0.0001||Gpp_Npp_QC_1km||Quality Control||Percent||8-bit unsigned integer||250 to 255||N/A||0 to 100||N/A|
|65530||Urban/built-up cover type|
|65531||Permanent wetlands/inundated marshland type|
|65532||Perennial snow or ice cover type|
|65533||Barren, sparsely vegetated (rock, tundra, desert) cover type|
|65534||Perennial salt or inland fresh water body cover type|
|65535||Fill value assigned to pixels not falling into other categories|
The improved, yearly MODIS GPP/NPP product does not use QA bit-fields but a meaningful percent value. 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 correspond to the different non-vegetated land cover types identified in table above.
|250||Urban/built-up cover type|
|251||Permanent wetlands/inundated marshland type|
|252||Perennial snow or ice cover type|
|253||Barren, sparsely vegetated (rock, tundra, desert) cover type|
|254||Perennial salt or inland fresh water body cover type|
|255||Fill value assigned to pixels not falling into other categories|
Information on accuracy can be found on the MODIS Land Validation Web Site.
For complete information about the MOD17A3 known issues please refer to the MODIS Land Quality Assessment website.