| Generally,there is an inconsistency between the total regional crop area that was obtained from remote sensing technology and the official statistical data on crop areas.This problem affects the application of remote sensing-based crop spatial distribution mapping results to a certain extent.To obtain high accuracy crop spatial distribution information consistent with the statistical data of crop planting area,this study took Wuyi County,Hengshui City,Hebei Province in the Huanghuaihai Plain of China as the study area,took the vegetation index time series as the research data.The visual interpretation data of the regional winter wheat planting area was taken as the total amount control data,supported by SCE-UA global optimization algorithm,CCSM algorithm and similarity indicator RMSE,a new method for extracting and mapping winter wheat spatial distribution was proposed in this study based on threshold optimization of NDVI time series similarity under regional crop planting area total amount control,and the accuracy was verified using the similarity of Sentinel-2 NDVI time series in the whole growth period.On this basis,a comparative analysis on the accuracy of winter wheat mapping results were carried out,which were extracted from the similarity and their combinations of NDVI time series at different growth stages.And the analysis of influencing factors of accuracy of the winter wheat distribution extraction and mapping method based on threshold optimization of NDVI time series similarity under regional crop planting area total amount control were also carried out.Finally,the spatial distribution of winter wheat in Huanghuaihai region were extracted.The main conclusions are as follows:(1)Based on Sentinel-2 NDVI time series data covering the whole growth period of winter wheat,this study took the visual interpretation data of winter wheat planting area in Wuyi County as total amount control data,SCE-UA algorithm,CCSM algorithm and similarity indicator RMSE were used to verify the spatial distribution extraction and mapping method of winter wheat based on threshold optimization of NDVI time series similarity under regional crop planting area total amount control.According to verification,the total area accuracy of the winter wheat mapping results using the similarity of Sentinel-2 NDVI time series in the whole growth period in Wuyi County was more than99.99%,the overall accuracy and Kappa coefficient were 98.08% and 0.96,respectively.It was proved that the proposed method could ensure the result consistency between the total area of regional crops obtained by remote sensing and the total amount control data,and higher recognition accuracy could be obtained.The results showed that the method was effective and feasible,and it could provide a certain reference for regional high-precision winter wheat distribution extraction and mapping under the support of complete remote sensing information.(2)Based on the division of Sentinel-2 NDVI time series data during the whole growth period of winter wheat in Wuyi County,took the visual interpretation data of winter wheat planting area in Wuyi County as total amount control data,and the comparison analysis on the accuracy of winter wheat mapping results of NDVI time series similarity and similarity combinations in different growth stages were carried out.Through validation,the NDVI time series from the seedling stage to the tillering stage before winter and from the reviving stage to the jointing stage could be used to obtain high accuracy crop distribution extraction results,while the NDVI time series from the heading stage to the maturity stage were used to extract winter wheat,the accuracy was low.Moreover,the comprehensive application of the similarity of NDVI time series at different growth stages was beneficial to the improvement of crop extraction and mapping accuracy to a certain extent.The above results could enhance the applicability of this research method,and could provide a certain reference for the selection of key growth stage data in the extraction and mapping of winter wheat distribution under the support of incomplete NDVI time series.(3)Took Sentinel-2 NDVI,Landsat-8 NDVI and MODIS NDVI as the main data,the visual interpretation data of winter wheat planting area under different error gradients as total amount control,and Hengshui City as the main research area,the analysis of the influence of the accuracy of extraction and mapping of winter wheat spatial distribution based on threshold optimization of NDVI time series similarity under regional crop planting area total amount control was performed.From the analysis results,when the study area was at county scale,the higher the spatial resolution of remote sensing image,and the closer the total amount control data to the true value,the higher the overall accuracy and Kappa coefficient of winter wheat spatial distribution extraction results.In addition,when the study area was at city scale,for medium and high-resolution images,when extracting the spatial distribution of winter wheat by counties in Hengshui City,the overall accuracy and Kappa coefficient of the extraction results were improved;while for low-resolution images,when extracting the spatial distribution of winter wheat by counties in Hengshui City,the overall accuracy and Kappa coefficient of the extraction results were decreased.The above conclusions could provide a theoretical basis for the large-scale application of this research method.(4)On the basis of putting forward,verifying the method and analyzing the influence factors of accuracy,according to the MODIS NDVI time series data and this research method,the extraction of the spatial distribution of winter wheat in the Huanghuaihai region in 2018 was carried out under the regional crop planting area statistical data total amount control.The verification results showed that the total area accuracy of the extraction results of the spatial distribution of winter wheat in each city in the Huanghuaihai region in 2018 was more than 99.90%,and the overall accuracy was more than 70%.The overall accuracy of the extraction results of the spatial distribution of the whole winter wheat in Huanghuaihai area was 85.51%,and the Kappa coefficient was 0.71,which further proved that the method of this research had certain validity and feasibility in the extraction of the spatial distribution of winter wheat in a large region.The classification accuracy could meet the needs of users for extracting and mapping the spatial distribution of winter wheat in large area. |
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