# Mapping Aquaculture Ponds for the Coastal Zone of Asia with Sentinel-1 and Sentinel-2 Time Series
## 2 Study Region  
In this study, we focus on the coastal zone of South Asia, Southeast Asia, and East Asia, which extends over 22 Asian countries and comprises a total coastline of 300,000 km (see Figure 3 and Table 1). We defined a coastal zone of Asia (CZA) by calculating a 200-km buffer--landwards and seawards--from a detailed coastline of Asia. Efficient coastal sections were designed in this study in order to enable processing of large satellite data time series for the entire coastal zone of Asia. For this purpose, the 200-km-wide coastal buffer was subdivided into 261 coastal parcels (see Figure 3) by calculating and digitizing lateral sections with a distance interval of 200 km coastline length. The final coastal zone stretches from Iran in the west to Western New Guinea in the southeast and Japan in the northeast and is inhabited by more than 1.7 billion people (see Table 1), which corresponds to almost a quarter (22 percent) of the current world population. The zone represents environments with different climates, different terrains, and a variety of terrestrial and aquatic ecosystems. Rapid socio-economic development, increased urbanization, and coast-ward migration [37], however, dramatically changed the coastal regions in Asia during the last two decades. Land use changes were closely related to the expanding farming of crops (e.g., paddy rice), fish and shrimp, which are the main food source for millions of people. For a more general spatial comparison in Section 4, we also defined five macro-regions (see Figure 3 for coverage and Table 1 for country codes):South Asia (IRN, PAK, IND, LKA, BGD), Southeast Asia Mainland (MYR, THA, KHM, VNM, West-MYS, SGP), Southeast Asia Maritime (East-MYS, IDN, PHIL, BRN, TLS), East Asia (CHN, MAC, HKG, TWN), and Northeast Asia (PRK, KOR, JPN). The coastal zone in South, East, and Southeast Asia with its variety of lagoons, estuaries, river deltas, and abundant water resources provides ideal conditions for breeding fish and crustaceans. Above all, the low-lying, flat-topography areas along the coastal regions fostered the rapid growth of pond aquaculture. As a result, the fertile and often densely populated coastal regions in Asia have experienced large-scale changes of land use and shifts in farming systems [8; 40], primarily through the expansion and intensification of agriculture and land-based aquaculture, which provide the staple foods for the majority of the coastal population. At the same time, the coastal zone is one of the most threatened regions in the context of global environmental changes and global climate change effects, such as increased frequency of weather extremes (floods, droughts, and storms) and salinization [9; 16; 41; 42]. Table 1 shows the main characteristics of the respective countries that cover the coastal study region. The large island state Indonesia with its coasts on Borneo, Sumatra, Java, Sulawesi and New Guinea has the longest coastline of all Asian countries, with a total length of 97,680 km. The total population of the coastal zone defined in this study makes up 41 percent of the total population of the countries that belong to this zone. More than half of the coastal countries (12 out of 22) have from 90 to 100 percent of their total population within 200 km of the coast (see Table 1).