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-biomes02160nas a2200229   4500008004100000245010200041210006900143300001500212490000700227520139300234100001601627700002301643700001701666700001601683700002001699700001801719700001901737700001801756700001401774700001601788856012601804       2006                        eng d00aMODIS land cover and LAI collection 4 product quality across nine sites in the western hemisphere0 aMODIS land cover and LAI collection 4 product quality across nin  a1843 -18570 v443 aGlobal maps of land cover and leaf area index (LAI) derived from the Moderate Resolution Imaging Spectrometer (MODIS) reflectance data are an important resource in studies of global change, but errors in these must be characterized and well understood. Product validation requires careful scaling from ground and related measurements to a grain commensurate with MODIS products. We present an updated BigFoot project protocol for developing 25-m validation data layers over 49-km2 study areas. Results from comparisons of MODIS and BigFoot land cover and LAI products at nine contrasting sites are reported. In terms of proportional coverage, MODIS and BigFoot land cover were in close agreement at six sites. The largest differences were at low tree cover evergreen needleleaf sites and at an Arctic tundra site where the MODIS product overestimated woody cover proportions. At low leaf biomass sites there was reasonable agreement between MODIS and BigFoot LAI products, but there was not a particular MODIS LAI algorithm pathway that consistently compared most favorably. At high leaf biomass sites, MODIS LAI was generally overpredicted by a significant amount. For evergreen needleleaf sites, LAI seasonality was exaggerated by MODIS. Our results suggest incremental improvement from Collection 3 to Collection 4 MODIS products, with some remaining problems that need to be addressed1 aCohen, W.B.1 aMaiersperger, T.K.1 aTurner, D.P.1 aRitts, W.D.1 aPflugmacher, D.1 aKennedy, R.E.1 aKirschbaum, A.1 aRunning, S.W.1 aCosta, M.1 aGower, S.T.  uhttp://knz.lternet.edu/content/modis-land-cover-and-lai-collection-4-product-quality-across-nine-sites-western-hemisphere03869nas a2200289   4500008004100000245017000041210006900211300001300280490000700293520292700300653001203227653000803239653000903247653001503256653002003271653001003291653001503301100001603316700002303332700001303355700001603368700001703384700001603401700002103417700001803438856012303456       2003                        eng d00aComparisons of land cover and LAI estimates derived from ETM+ and MODIS for four sites in North America: a quality assessment of 2000/2001 provisional MODIS products0 aComparisons of land cover and LAI estimates derived from ETM and  a221 -3620 v883 aThe MODIS land science team produces a number of standard products, including land cover and leaf area index (LAI). Critical to the success of MODIS and other sensor products is an independent evaluation of product quality. In that context, we describe a study using field data and Landsat ETM+ to map land cover and LAI at four 49-km2 sites in North America containing agricultural cropland (AGRO), prairie grassland (KONZ), boreal needleleaf forest, and temperate mixed forest. The purpose was to: (1) develop accurate maps of land cover, based on the MODIS IGBP (International Geosphere–Biosphere Programme) land cover classification scheme; (2) derive continuous surfaces of LAI that capture the mean and variability of the LAI field measurements; and (3) conduct initial MODIS validation exercises to assess the quality of early (i.e., provisional) MODIS products. ETM+ land cover maps varied in overall accuracy from 81% to 95%. The boreal forest was the most spatially complex, had the greatest number of classes, and the lowest accuracy. The intensive agricultural cropland had the simplest spatial structure, the least number of classes, and the highest overall accuracy. At each site, mapped LAI patterns generally followed patterns of land cover across the site. Predicted versus observed LAI indicated a high degree of correspondence between field-based measures and ETM+ predictions of LAI. Direct comparisons of ETM+ land cover maps with Collection 3 MODIS cover maps revealed several important distinctions and similarities. One obvious difference was associated with image/map resolution. ETM+ captured much of the spatial complexity of land cover at the sites. In contrast, the relatively coarse resolution of MODIS did not allow for that level of spatial detail. Over the extent of all sites, the greatest difference was an overprediction by MODIS of evergreen needleleaf forest cover at the boreal forest site, which consisted largely of open shrubland, woody savanna, and savanna. At the agricultural, temperate mixed forest, and prairie grassland sites, ETM+ and MODIS cover estimates were similar. Collection 3 MODIS-based LAI estimates were considerably higher (up to 4 m2 m−2) than those based on ETM+ LAI at each site. There are numerous probable reasons for this, the most important being the algorithms' sensitivity to MODIS reflectance calibration, its use of a prelaunch AVHRR-based land cover map, and its apparent reliance on mainly red and near-IR reflectance. Samples of Collection 4 LAI products were examined and found to consist of significantly improved LAI predictions for KONZ, and to some extent for AGRO, but not for the other two sites. In this study, we demonstrate that MODIS reflectance data are highly correlated with LAI across three study sites, with relationships increasing in strength from 500 to 1000 m spatial resolution, when shortwave-infrared bands are included.10aBigFoot10aETM10aIGBP10aLand cover10aLeaf area index10aMODIS10aValidation1 aCohen, W.B.1 aMaiersperger, T.K.1 aYang, Z.1 aGower, S.T.1 aTurner, D.P.1 aRitts, W.D.1 aBerterretche, M.1 aRunning, S.W.  uhttp://knz.lternet.edu/content/comparisons-land-cover-and-lai-estimates-derived-etm-and-modis-four-sites-north-america