Policy-driven opposite changes of coastal aquaculture ponds between China and Vietnam: Evidence from Sentinel-1 images.

Coastal aquaculture ponds (CAPs) are of great importance for food security, ecosystem health, and greenhouse emissions. However, existing data often lacks geographic information on both national and international scale spatial data. Satellite remote sensing makes large-scale monitoring of CAPs more efficient. This is especially true when using synthetic aperture radar (SAR) data, which can provide all-day acquisition as a high-quality data source for large-scale CAP mapping. In this study, focusing on CAPs in China and Vietnam, a novel method of large-scale CAPs mapping using Sentinel-1 images was developed. Moreover, high-resolution (10 m) CAP datasets in 2015 and 2020 were produced, and spatiotemporal changes and drivers were analyzed. The key results are as follows: (1) the overall accuracy of the mapping method proposed was >90%. (2) In 2020, CAP area in China was 8774.93 km2 (69.43%) and it was 3864.10 km2 (30.57%) in Vietnam. (3) CAPs showed an opposite trend in China and Vietnam. The CAP area decreased by 891.29 km2 with a change rate of about −9.22% in China, while the CAP area increased by 920.35 km2 with a change rate of about 31.26% in Vietnam. China had made unprecedented ecofriendly efforts to restrict expansion for improving the ecological environment. Vietnam focused more on increasing production than on environmental protection, leading to significant expansion. Our results offer some new insights on satellite remote sensing and its use in coastal eco-environmental management and contribute to Sustainable Development Goals 2, 6 and 14. • An approach for large-scale mapping coastal aquaculture ponds using Sentinel-1. • High-resolution (10 m) distribution maps of CAPs were obtained. • Change trend of CAPs from 2015 to 2020 in China and Vietnam was opposite. • Different policies were the key factor driving for CAPs changes. [ABSTRACT FROM AUTHOR]