Estimating winter wheat straw amount and spatial distribution in Qihe County, China, using GF-1 satellite images

Crop straw is considered an important renewable energy source. China produces approximately one billion tons of crop straw annually, but 35% of this yield is not used effectively. In this study, a novel method for estimating the regional winter wheat straw yield was developed to promote straw resource recovery. Medium resolution (16 m) GF-1 satellite images of Qihe County were obtained. A weighted normalized difference vegetation index (WNDVI) image of winter wheat based on time-series normalized difference vegetation index values was generated by weighting samples to distinguish winter wheat from other land cover types, such as woodland, bare land, water, settlement, and other cultivated land. Four kernel functions of support vector machines (SVMs) were used for image classification. The linear kernel function with the highest accuracy was selected to construct the extraction model of the winter wheat plantation area in the Qihe County, Shandong Province, China, and the estimation method for total theoretical resources and spatial distribution of winter wheat straw in the region was established. The results show that the winter wheat straw in the Qihe County was mainly concentrated in the central and southern regions followed by the northern region; the central urban districts in the central-north region had the lowest straw concentration. The theoretical total quantity of straw resources of winter wheat in the county was 690 497 t; and the theoretical recoverable resource quantity was 504 063 t. The error between the estimated data and statistical data was only 1.27%, indicating that SVM and WNDVI can accurately identify winter wheat and estimate the spatial distribution of winter wheat straw in Qihe County.