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An Evaluation of MODIS 250-m Data for Green LAI Estimation in Crops

An Evaluation of MODIS 250-m Data for Green LAI Estimation in Crops
【摘要】: 

Green leaf area index (LAI) is an important variable for climate modeling, estimates of primary production, agricultural yield forecasting, and many other diverse applications. Remotely sensed data provide considerable potential for estimating LAI at local, regional, and global scales. The goal of this study was to retrieve green LAI from MODIS 250-m vegetation index (VI) data for irrigated and rainfed maize and soybeans. The performance of both MODIS-derived NDVI and Wide Dynamic Range Vegetation Index (WDRVI) were evaluated across three growing seasons (2002 through 2004) over a wide range of LAI and also compared to the performance of NDVI and WDRVI derived from reflectance data collected at closerange across the same field locations. The NDVI vs. LAI relationship showed asymptotic behavior with a sharp decrease in the sensitivity of the NDVI to LAI exceeding 2 m2/m2 for both crops. WDRVI vs. LAI relation was linear across the entire range of LAI variation with determination coefficients above 0.93. Importantly, the coefficients of the close-range WDRVI vs. LAI equation and the MODISretrieved WDRVI vs. LAI equation were very close. The WDRVI was found to be capable of accurately estimating LAI across a much greater LAI range than the NDVI and can be used for assessing even slight variations in LAI, which are indicative of the early stages of plant stress. These results demonstrate the new possibilities for analyzing the spatio-temporal variation of the LAI of crops using multi-temporal MODIS 250-m imagery.

文章编号: 
doi:10.1029/2007GL031620

One of the key variables required for estimating primary production and global climate studies is leaf area index (LAI). Remote estimations of LAI at regional to global scales can be performed using transforms of spectral reflectance, called vegetation indices (VIs) [e.g., Rouse et al., 1974]. A physically-based algorithm for estimating LAI from NDVI observations has been developed [e.g., Myneni et al., 1997]. However, the relationship between NDVI and LAI is essentially non-linear and suffers a rapid decrease of sensitivity at moderate-to-high densities of photosynthetic green biomass [Asrar et al., 1984; Goward and Huemmerich, 1992; Myneni et al., 1997; Gitelson et al., 2003; Gitelson, 2004].

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