NASA Technical Reports Server NTRS 20150000292: Estimation of Crop Gross Primary Production GPP. 2; Do Scaled MODIS Vegetation Indices Improve PerformanceReportar como inadecuado



 NASA Technical Reports Server NTRS 20150000292: Estimation of Crop Gross Primary Production GPP. 2; Do Scaled MODIS Vegetation Indices Improve Performance


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Satellite remote sensing estimates of Gross Primary Production GPP have routinely been made using spectral Vegetation Indices VIs over the past two decades. The Normalized Difference Vegetation Index NDVI, the Enhanced Vegetation Index EVI, the green band Wide Dynamic Range Vegetation Index WDRVIgreen, and the green band Chlorophyll Index CIgreen have been employed to estimate GPP under the assumption that GPP is proportional to the product of VI and photosynthetically active radiation PAR where VI is one of four VIs: NDVI, EVI, WDRVIgreen, or CIgreen. However, the empirical regressions between VI*PAR and GPP measured locally at flux towers do not pass through the origin i.e., the zero X-Y value for regressions. Therefore they are somewhat difficult to interpret and apply. This study investigates 1 what are the scaling factors and offsets i.e., regression slopes and intercepts between the fraction of PAR absorbed by chlorophyll of a canopy fAPARchl and the VIs, and 2 whether the scaled VIs developed in 1 can eliminate the deficiency and improve the accuracy of GPP estimates. Three AmeriFlux maize and soybean fields were selected for this study, two of which are irrigated and one is rainfed. The four VIs and fAPARchl of the fields were computed with the MODerate resolution Imaging Spectroradiometer MODIS satellite images. The GPP estimation performance for the scaled VIs was compared to results obtained with the original VIs and evaluated with standard statistics: the coefficient of determination R2, the root mean square error RMSE, and the coefficient of variation CV. Overall, the scaled EVI obtained the best performance. The performance of the scaled NDVI, EVI and WDRVIgreen was improved across sites, crop types and soil-background wetness conditions. The scaled CIgreen did not improve results, compared to the original CIgreen. The scaled green band indices WDRVIgreen, CIgreen did not exhibit superior performance to either the scaled EVI or NDVI in estimating crop daily GPP at these agricultural fields. The scaled VIs are more physiologically meaningful than original un-scaled VIs, but scaling factors and offsets may vary across crop types and surface conditions.



Autor: NASA Technical Reports Server (NTRS)

Fuente: https://archive.org/







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