Period: 2000 – present
Sensor: MODIS Terra+Aqua
Data can be accessed here.
Algorithm description: MOD17A2H is 8-Day GPP composite and it is calculated based on ‘radiation conversion theory’. It uses MODIS FPAR product and independently estimated PAR. Conversion of PAR to GPP requires FAPAR and radiation conversion efficiency. This parameter is also modified as a function of temperature and water pressure deficit stress factors. The parameter values are biome specific and are derived empirically from Biome-BGC model simulations. The respiration components (maintenance and growth) are calculated by allometric relationships between MODIS LAI and annual growth rates (based on Biome BGC simulations). All the requisite parameters are used from the Biome-BGC model. The biome characterisation is done using MODIS land-cover map.
Accuracy: Heinsch et al (2006) report that the MODIS annual GPP algorithm had strong correlation (r = 0.859) with tower based annual GPP over a range of eddy covariance sites. However MOD17 (earlier versions) have been found to be overestimating GPP for most of the sites, except most productive sites where it is underestimated. Authors also show that use of DAO meteorological data (as in MODIS algorithm) leads to about 28 to 45% error in GPP against the tower based meteorology input simulations. They found that the role of land cover related errors were reasonably small, but other sources of errors such as errors in the MODIS LAI product, FAPAR product and also scaling related issues with Biome-BGC model parameters and allometric equations could have significant effect on the accuracy.
Turner et al (2006) also report no overall bias in the MODIS NPP and GPP but overestimation in low productive sites.
- Validation is not available for recent version of the product.
- Product is prone to error propagation considering applications of MODIS LAI, FPAR and Landcover map as as well as global PAR data.
Heinsch, F. A. et al. Evaluation of remote sensing based terrestrial productivity from MODIS using regional tower eddy flux network observations. IEEE Trans. Geosci. Remote Sens. 44,1908–1925 (2006).
Turner, D. P. et al. Evaluation of MODIS NPP and GPP products across multiple biomes. Remote Sens. Environ. 102, 282–292 (2006).
Running, S. W., Nemani, R., Glassy, J. M. & Thornton, P. E. MODIS Daily Photosynthesis (PSN) and Annual Net Primamy Production (NPP) Product (MOD17) Algorithm Theoretical Basis Document Version 3.0. 1–59 (1999).