Abstract
The net primary productivity (NPP) and aboveground biomass mapping of crops based on remote sensing technology are not only conducive to understanding the growth and development of crops but can also be used to monitor timely agricultural information, thereby providing effective decision making for agricultural production management. To solve the saturation problem of the NDVI in the aboveground biomass mapping of crops, the original CASA model was improved using narrow-band red-edge information, which is sensitive to vegetation chlorophyll variation, and the fraction of photosynthetically active radiation (FPAR), NPP, and aboveground biomass of winter wheat and maize were mapped in the main growing seasons. Moreover, in this study, we deeply analyzed the seasonal change trends of crops’ biophysical parameters in terms of the NDVI, FPAR, actual light use efficiency (LUE), and their influence on aboveground biomass. Finally, to analyze the uncertainty of the aboveground biomass mapping of crops, we further discussed the inversion differences of FPAR with different vegetation indices. The results demonstrated that the inversion accuracies of the FPAR of the red-edge normalized vegetation index (NDVIred-edge) and red-edge simple ratio vegetation index (SRred-edge) were higher than those of the original CASA model. Compared with the reference data, the accuracy of aboveground biomass estimated by the improved CASA model was 0.73 and 0.70, respectively, which was 0.21 and 0.13 higher than that of the original CASA model. In addition, the analysis of the FPAR inversions of different vegetation indices showed that the inversion accuracies of the red-edge vegetation indices NDVIred-edge and SRred-edge were higher than those of the other vegetation indices, which confirmed that the vegetation indices involving red-edge information can more effectively retrieve FPAR and aboveground biomass of crops.
Highlights
Remote sensing technology is widely used in crop yield prediction [1,2,3,4,5], identification mapping [6,7,8], aboveground biomass estimation [9,10], leaf area index (LAI) inversion [11,12,13,14], and many other fields of agricultural production, and it has always been the focus of attention in studies of crop biomass [2,15,16]
The red-edge band is an essential variable for retrieving the LAI, fraction of photosynthetically active radiation (FPAR), etc., and it plays an important role in biomass estimation
Aboveground biomass mapping is crucial for agricultural production management and food security, and the CASA model provides important support for this purpose
Summary
Remote sensing technology is widely used in crop yield prediction [1,2,3,4,5], identification mapping [6,7,8], aboveground biomass estimation [9,10], LAI inversion [11,12,13,14], and many other fields of agricultural production, and it has always been the focus of attention in studies of crop biomass [2,15,16]. The vegetation index regression methods can quickly obtain crop biomass information, but these methods require large amounts of measured data, and their performance is not accurate when applied at global or national scales. Much of research has demonstrated that the wide-band vegetation index, NDVI, is saturated in areas of dense vegetation and irrigation scale By applying this model to small areas, high-resolution biomass mapping will help expand the usage of the CASA model. The wide-band vegetation results to theisestimation of NPP biomass of cropsCASA, in a small irrigation index, NDVI, used to retrieve theand key aboveground parameter, FPAR, in the original which scale region. NPP and aboveground biomass of crops in a small irrigation scale region
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