Twenty-meter annual paddy rice area map for mainland Southeast Asia using Sentinel-1 synthetic-aperture-radar data

Abstract

Abstract. Over 90 % of the world's rice is produced in the Asia–Pacific region. Synthetic-aperture radar (SAR) enables all-day and all-weather observations of rice distribution in tropical and subtropical regions. The complexity of rice cultivation patterns in tropical and subtropical regions makes it difficult to construct a representative data-relevant rice crop model, increasing the difficulty in extracting rice distributions from SAR data. To address this problem, a rice area mapping method for large regional tropical or subtropical areas based on time-series Sentinel-1 SAR data is proposed in this study. Based on the analysis of rice backscattering characteristics in mainland Southeast Asia, the combination of spatiotemporal statistical features with good generalization ability was selected and then input into the U-Net semantic segmentation model, combined with WorldCover data to reduce false alarms, finally the 20 m resolution rice area map of five countries in mainland Southeast Asia in 2019 was obtained. The proposed method achieved an accuracy of 92.20 % on the validation sample set, and the good agreement was obtained when comparing our rice area map with statistical data and other rice area maps at the national and provincial levels. The maximum coefficient of determination R2 was 0.93 at the national level and 0.97 at the provincial level. These results demonstrate the advantages of the proposed method in rice area mapping with complex cropping patterns and the reliability of the generated rice area maps. The 20 m annual paddy rice area map for mainland Southeast Asia is available at https://doi.org/10.5281/zenodo.7315076 (Sun et al., 2022b).

SEA-Rice-Ci10: High-resolution Mapping of Rice Cropping Intensity and Harvested Area Across Southeast Asia using the Integration of Sentinel-1 and Sentinel-2 Data

“…SAR data may penetrate cloud cover and supplement optical data in continuous Earth surface monitoring to correct for missed phenological phenomena. The accuracy of rice identification with integrated Sentinel-1 and Sentinel-2 images is greater than with Sentinel-1 or Sentinel-2 images alone (Jiang et al, 2023).…”

“…This map, referred to as the "NESEA-Rice10", covers monsoon Asia, including Southeast Asia and Northeast Asia, with a spatial resolution of 10 meters. The second map was created using Sentinel-1 data collected in 2019 by Sun et al (2023) for mainland Southeast Asia, and the data was downloaded from https://doi.org/10.5281/zenodo.7315076 and is referred as "20mRice-MSEAsia". Both maps present rice-growing areas rather than rice cropping intensity or harvest areas.…”

“…The accuracy of our produced maps was evaluated using two types of assessment: (1) comparison with statistical data and other rice maps at the national, provincial, and regency levels (Table 2), and (2) comparison with existing rice maps by NESEA-Rice10 (Han et al, 2021) and 20mRice-MSEAsia (Sun et al, 2023). We used the coefficient of determination (R 2 ) to measure the correlation between our paddy rice maps, agricultural statistics, and existing products using the following equation.…”

“…Sentinel-1 data is widely used to map rice extents, especially in tropical regions because the C-band SAR sensor can obtain data through cloud cover (Clauss et al, 2018;Rudiyanto et al, 2019;Singha et al, 2019;Vuong et al, 2019;Phan et al, 2021;Xu et al, 2021;Phung et al, 2022;Sun et al, 2023). In an earlier study, the 20mRice-MSEAsia using Sentinel-1 data calculated the total area of rice fields in mainland Southeast Asia is 25,150 x 10 3 ha (Sun et al, 2023). This value is greater than the rice growing area estimated in this study (22,496 x 10 3 ha).…”

Timing of Global Surface Water Transitions Reveals Anthropogenic Dominance of Recent Growth in Water Extent

“…These dam constructions certainly played a role in the surpassing of the accumulated areas of advance over accumulated areas of recession in the different continents of the world, such as North America, which transitioned to this state in 2002, Africa (transitioned in 2000), South Asia (transitioned 2011), East and Southeast Asia (transitioned in 2002), and Central Asia (transitioned 1993). In East Asia, in addition to the surge of dams 48 and the spread of ooded agriculture (more than 90% of the global rice is produced in the Asia-Paci c region 49 ), climate change is also impacting the rates of precipitation and ice melting, which are lling up the natural lakes of the Tibetan Plateau 42,43 . Furthermore, in North America, despite the water retreat observed on the US West Coast (mainly before 2010), the lling of prairie potholes in North Dakota in 2012, mainly caused by higher precipitation 44,45 , also contributed to the positive surface water balance of the continent.…”