# Mapping Aquaculture Ponds for the Coastal Zone of Asia with Sentinel-1 and Sentinel-2 Time Series
###### Abstract  
Asia dominates the world's aquaculture sector, generating almost 90 percent of its total annual global production. Fish, shrimp, and mollusks are mainly farmed in land-based pond aquaculture systems and serve as a primary protein source for millions of people. The total production and area occupied for pond aquaculture has expanded rapidly in coastal regions in Asia since the early 1990s. The growth of aquaculture was mainly boosted by an increasing demand for fish and seafood from a growing world population. The aquaculture sector generates income and employment, contributes to food security, and has become a billion-dollar industry with high socio-economic value, but has also led to severe environmental degradation. In this regard, geospatial information on aquaculture can support the management of this growing food sector for the sustainable development of coastal ecosystems, resources, and human health. With free and open access to the rapidly growing volume of data from the Copernicus Sentinel missions as well as machine learning algorithms and cloud computing services, we extracted coastal aquaculture at a continental scale. We present a multi-sensor approach that utilizes Earth observation time series data for the mapping of pond aquaculture within the entire Asian coastal zone, defined as the onshore area up to 200 km from the coastline. In this research, we developed an object-based framework to detect and extract aquaculture at a single-pond level based on temporal features derived from high-spatial-resolution SAR and optical satellite data acquired from the Sentinel-1 and Sentinel-2 satellites. In a second step, we performed spatial and statistical data analyses of the Earth-observation-derived aquaculture dataset to investigate spatial distribution and identify production hotspots at various administrative units at regional, national, and sub-national scale. a 20221 2021  
With a share of 88 percent (75 million tons) of the global total volume [1], Asia is the world's largest regional aquaculture producer and has been the major driver of global aquaculture growth in recent years (see Figure 1). Land-based pond culture of fish and shrimp in fresh water and brackish water has a long tradition in Asia and has contributed most to Asia's dominant role in aquaculture production. In Asia, aquaculture has expanded rapidly since the 1990s along the coasts, especially those of Southeast Asia and East Asia [8], and become a major protein source for millions of people. Aquaculture has become a billion-dollar industry with high socio-economic value, generates income and employment, and contributes to food security. However, the expansion of aquaculture in low-lying, flat-topography coastal regions has also led to large-scale land use changes with various negative socio-economic and environmental effects: the enormous reclamation of land for fish and shrimp ponds, increasing use of antibiotics and pesticides, water pollution, the loss of valuable coastal wetlands, and the degradation of important ecosystems (due to increased salinization of soils and freshwater, wastewater discharge, and eutrophication of coastal waters), among other effects, result from rapidly growing aquaculture production [9; 10; 11]. Moreover, large amounts of nutrient-rich feed [12; 13] and medication are applied in intensive aquaculture to achieve high stocking densities and increase production quantities, but they lead to increased nutrient input, eutrophication, and water pollution of the aquatic coastal ecosystems [13; 14; 15]. Consequently, sustainable aquaculture management is essential to reduce the growing ecological footprint of Asian aquaculture and a global challenge for future food security. In addition, the coastal regions are particularly vulnerable to the consequences of climate change: global warming, rising sea levels, rising water temperatures, salinization, acidification, and oxygen depletion in coastal waters can lead to yield losses with far-reaching economic consequences for the aquaculture industry [16].