Abstract:
Abstract: Geospatial information of irrigated cropland is necessary for the formulation of food policy, water management and climate change studies. In addition to those methods based on pure image classification or non-remote sensing data, spatial reconstruction of statistics by using remote sensing features, a branch of multi-data fusion, with the advantages of less relying on the sampling points with a good consistency with the statistical data, has played an important role in land cover mapping. However, it gains less attention in regional irrigated cropland extraction, which makes it unclear about its applicability in different regions. In this paper, we firstly tested a fusion method based on NDVI data and statistical data of spatial distribution of irrigated cropland in China. Then, quantitative and spatial accuracy assessment and comparisons with other datasets were also carried out for the sake of discussing the availability of the map. Finally, the possible factors reducing the accuracy of classification were discussed. The results showed that the ratio of irrigation farming decreased and the fragmentation of irrigated croplands increased gradually from east to west. Huang-Huai-Hai and Yangtze River plant regions were the places with the most concentrated irrigation. While in the locations with low precipitation such as northeastern and northwestern areas, irrigation farming was distributed along local water resources. Those irrigation areas were all consistent with the recognized irrigation areas. Quantitatively, the relative errors of more than 90% counties were within 5%, and most of the counties with high relative error (>30%) belonged to Shanxi while the rest were shared by several other provinces. From the view of absolute error, the number of negative ones was much less than positive ones, and this rule was also appropriate on province scale. The total spatial accuracy of the new map was 64.20%, but the values ranged from 31.21% to 90.64% on province scale. Provinces with the accuracies higher than average level were mostly distributed in the eastern areas of the country, and the precision level went lower from north to south. Meanwhile, there was no apparent geographical rule in west. Referring to the comparisons with similar datasets, this fusion method of statistic and remote sensing data could not only perform better quantitatively, but also provide more spatial details than data fusion method without satellite images. In addition, it maintained a same spatial accuracy level with the image classification but accelerated the operating process. These indicated that, the output of the method was both quantitatively and qualitatively comparable to that of similar method in China, yet there was a certain distance with its first application in America. Analysis suggested that, the cropland mask, the method hypothesis and the selected features are the major factors which largely influence the mapping accuracy, so the improvement of the method relies on better cropland maps, and optimization of geographical and spectral features.