Observations from satellite remote sensing provide important tools for regional and
global monitoring of terrestrial ecosystems. This article evaluated a recently developed vegetation
index (VI) model that estimates gross primary production (GPP) in an open grassland using
flux measurements and 250-m moderate-resolution imaging spectroradiometer (MODIS)
images. Two VIs, the two-band enhanced vegetation index (EVI2) and the normalized difference
vegetation index (NDVI), were tested as indicators of both fraction of absorbed photosynthetic
active radiation (f APAR) and light use efficiency (LUE). The standard MODIS GPP product was
moderately correlated with flux-measured GPP as indicated by the coefficients of determination
(R2) of 0.56 and a root mean square error (RMSE) of 15.4 gCm−2 8d−1. In comparison, results
suggested that the VI model can provide improved estimates of GPP, with R2 of 0.80, 0.82, and
0.81 for EVI2 × EVI2 × photosynthetically active radiation (PAR), NDVI × EVI2 × PAR, and
NDVI × NDVI × PAR, respectively. The underlying reason was that both EVI2 and NDVI were
potential proxies of f APAR (R2 of 0.43 and 0.53, respectively) and LUE (R2 of 0.52 and 0.46,
respectively). The primary analysis will be helpful for spatial improvements of future GPP
models.
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