Abstract
Paddy fields play very important environmental roles in food security, water resource management, biodiversity conservation, and climate change. Therefore, reliable broad-scale paddy field maps are essential for understanding these issues related to rice and paddy fields. Here, we propose a novel paddy field mapping method that uses Sentinel-1 synthetic aperture radar (SAR) time series that are robust for cloud cover, supplemented by Sentinel-2 optical images that are more reliable than SAR data for extracting irrigated paddy fields. Paddy fields were provisionally specified by using the Sentinel-1 SAR data and a conventional decision tree method. Then, an additional mask using water and vegetation indexes based on Sentinel-2 optical images was overlaid to remove non-paddy field areas. We used the proposed method to develop a paddy field map for Japan in 2018 with a 30 m spatial resolution. The producer’s accuracy of this map (92.4%) for non-paddy reference agricultural fields was much higher than that of a map developed by the conventional method (57.0%) using only Sentinel-1 data. Our proposed method also reproduced paddy field areas at the prefecture scale better than existing paddy field maps developed by a remote sensing approach.
Highlights
Rice is a staple food for billions of people especially in Asia, and paddy fields play important environmental roles by regulating water and energy budgets and supporting local biodiversity [1,2,3]
Through developing paddy field maps for Japan, this study demonstrated the potential of our novel paddy field mapping method using the Sentinel-1 time series supplemented by Sentinel-2 optical images in comparison with the conventional paddy field method using only Sentinel-1 time series data
By comparing our maps with existing paddy field maps and MAFF data on paddy field areas, we evaluated the reproducibility of our paddy field map
Summary
Rice is a staple food for billions of people especially in Asia, and paddy fields play important environmental roles by regulating water and energy budgets and supporting local biodiversity [1,2,3]. Paddy fields have cultural and esthetic values, as several traditional ones were awarded as Globally Important Agricultural Heritage [4]. According to the fifth assessment report of the Intergovernmental Panel on Climate Change, global emissions from paddy fields are estimated to be 33 to 40 Tg (CH4)/yr, or approximately 12% of total anthropogenic methane emissions [5]. In Japan, methane emissions from paddy fields account for more than 45% of total anthropogenic methane emissions [6]. Regional methane budgets strongly depend on the paddy field distribution. High-accuracy mapping of broad-scale paddy fields is of fundamental importance for understanding these issues related to rice and paddy fields
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