02770nas a2200337   4500008004100000245006800041210006800109300001300177490000800190520183400198653001102032653001102043653002902054653001202083653001002095653001502105653002702120653001502147100001702162700001602179700001602195700001602211700001702227700001302244700001602257700001902273700001402292700001602306700001402322856009602336       2006                        eng d00aEvaluation of MODIS NPP and GPP products across multiple biomes0 aEvaluation of MODIS NPP and GPP products across multiple biomes  a282 -2920 v1023 aEstimates of daily gross primary production (GPP) and annual net primary production (NPP) at the 1 km spatial resolution are now produced operationally for the global terrestrial surface using imagery from the MODIS (Moderate Resolution Imaging Spectroradiometer) sensor. Ecosystem-level measurements of GPP at eddy covariance flux towers and plot-level measurements of NPP over the surrounding landscape offer opportunities for validating the MODIS NPP and GPP products, but these flux measurements must be scaled over areas on the order of 25 km2 to make effective comparisons to the MODIS products. Here, we report results for such comparisons at 9 sites varying widely in biome type and land use. The sites included arctic tundra, boreal forest, temperate hardwood forest, temperate conifer forest, tropical rain forest, tallgrass prairie, desert grassland, and cropland. The ground-based NPP and GPP surfaces were generated by application of the Biome-BGC carbon cycle process model in a spatially-distributed mode. Model inputs of land cover and leaf area index were derived from Landsat data. The MODIS NPP and GPP products showed no overall bias. They tended to be overestimates at low productivity sites — often because of artificially high values of MODIS FPAR (fraction of photosynthetically active radiation absorbed by the canopy), a critical input to the MODIS GPP algorithm. In contrast, the MODIS products tended to be underestimates in high productivity sites — often a function of relatively low values for vegetation light use efficiency in the MODIS GPP algorithm. A global network of sites where both NPP and GPP are measured and scaled over the local landscape is needed to more comprehensively validate the MODIS NPP and GPP products and to potentially calibrate the MODIS NPP/GPP algorithm parameters.10abiomes10aGlobal10aGross primary production10aLandsat10aMODIS10aMonitoring10aNet primary production10aValidation1 aTurner, D.P.1 aRitts, W.D.1 aCohen, W.B.1 aGower, S.T.1 aRunning, SW.1 aZhao, M.1 aCosta, M.H.1 aKirschbaum, A.1 aHam, J.M.1 aSaleska, S.1 aAhl, D.E.  uhttp://knz.lternet.edu/content/evaluation-modis-npp-and-gpp-products-across-multiple-biomes