Abstract
Sugarcane is an important sugar and biofuel crop with high socio-economic importance, and its planted area has increased rapidly in recent years. China is the world’s third or fourth sugarcane producer. However, to our knowledge, no study has investigated the mapping of sugarcane cultivation areas across entire China. In this study, we developed a phenology-based method to identify sugarcane plantations in China at 30-m spatial resolution from 2016–2020 using the time-series of Landsat and Sentinel-1/2 images derived from Google Earth Engine (GEE) platform. The method worked by comparing the phenological similarity in normalized difference vegetation index (NDVI) series between unknown pixels and sugarcane samples. The phenological similarity was assessed using the time-weighted dynamic time warping method (TWDTW), which has less sensitivity to training samples than machine learning methods and therefore can be easily applied to large areas with limited samples. More importantly, our method introduced multiple and moving time standard phenological curves of sugarcane to the TWDTW by fully considering the variable crop life-cycle of sugarcane, particularly its long harvest season spanning from December to March of the following year. Validations showed the method performed well in 2019, with overall accuracies of 93.47% and 92.74% for surface reflectance (SR) and top of atmosphere reflectance (TOA) data, respectively. The sugarcane maps agreed well with the agricultural statistical areas from 2016–2020. The mapping accuracies using TOA data were comparable to SR data in 2019–2020, but outperformed SR data in 2016–2018 when SR data had lower availability on GEE. The sugarcane maps produced in this study can be used to monitor growing conditions and production of sugarcane and, therefore, can benefit sugarcane management, sustainable sugarcane production, and national food security.
Highlights
IntroductionSugarcane (Saccharum officinarum) is a semi-perennial crop with high socio-economic importance planted across tropical and subtropical regions of the world [1]
Sugarcane biofuel is an alternative energy source that can contribute to reducing greenhouse gases (GHG) emissions associated with fossil fuel combustion [5–7]
Based on the validations at pixel level using field samples from field surveys and Google Earth in 2019, the producer’s, user’s, and overall accuracies were 86.76%, 88.30%, and 93.47% with surface reflectance (SR) data; and 85.63%, 86.73%, and 92.74% with top of atmosphere reflectance (TOA) data for sugarcane in China, respectively
Summary
Sugarcane (Saccharum officinarum) is a semi-perennial crop with high socio-economic importance planted across tropical and subtropical regions of the world [1]. Sugarcane can be used to produce sugar and provides over 70% of the world’s sugar production [2,3]. Sugarcane residues are rich in cellulose and hemicellulose, which can be used to produce bioethanol and other liquid transportation biofuels [4]. Sugarcane biofuel is an alternative energy source that can contribute to reducing greenhouse gases (GHG) emissions associated with fossil fuel combustion [5–7]. Sugarcane bioethanol could reduce fossil fuel GHG emissions by 85% in Brazil [8]. Sugarcane expanded rapidly in the past decades by Remote Sens.
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