Reconstruction of the Water Cultivation Paleoenvironment Dating Back to the Han and Tang Dynasties Surrounding the Yangguan Frontier Pass Using X- and L-Band SAR Data

Supported by a shallow groundwater wetland ecosystem, the Nanhu oasis, which is the location of the Yangguan frontier pass, represents an important supply and defence station for the ancient Silk Road. The reconstruction of the evolution of the water cultivation environment is helpful for archaeological surveys and the protection of this well-known heritage site. This study proposes a workflow for reconstructing the water cultivation paleoenvironment-based primarily on X- and L-band spaceborne synthetic aperture radar (SAR) data. First, TerraSAR-X/TanDEM-X (TSX/TDX)-generated Digital Elevation Model (DEM) data were used for microrelief analyses, including a watershed analysis and drainage network extraction. Several dried-up paleochannels and the range of the Daze (a wetland dating back to the Tang Dynasty (618–907 A.D.)) were identified. Second, based on the hydrological sensitivity analysis of the multi-temporal L-band SAR data, arid land vegetation accompanying the emergence of groundwater was extracted to locate ancient arable areas using backscattering and coherence characteristics. Finally, reconstruction of the water cultivation paleoenvironment surrounding the Nanhu oasis dating back to the Han and Tang dynasties (202 B.C.–907 A.D.) was performed, referring to historical documents. New discoveries were validated by field campaigns, and the results of the SAR archaeological investigations conducted in this study indicated that the ancient arable area in the Nanhu oasis was nearly double the current dimensions

Spaceborne L-Band Synthetic Aperture Radar Data for Geoscientific Analyses in Coastal Land Applications: A Review

The coastal zone offers among the world’s most productive and valuable ecosystems and is experiencing increasing pressure from anthropogenic impacts: human settlements, agriculture, aquaculture, trade, industrial activities, oil and gas exploitation and tourism. Earth observation has great capability to deliver valuable data at the local, regional and global scales and can support the assessment and monitoring of land‐ and water‐related applications in coastal zones. Compared to optical satellites, cloud‐cover does not limit the timeliness of data acquisition with spaceborne Synthetic Aperture Radar (SAR) sensors, which have all‐weather, day and night capabilities. Hence, active radar systems demonstrate great potential for continuous mapping and monitoring of coastal regions, particularly in cloud‐prone tropical and sub‐tropical climates. The canopy penetration capability with long radar wavelength enables L‐band SAR data to be used for coastal terrestrial environments and has been widely applied and investigated for the following geoscientific topics: mapping and monitoring of flooded vegetation and inundated areas; the retrieval of aboveground biomass; and the estimation of soil moisture. Human activities, global population growth, urban sprawl and climate change‐induced impacts are leading to increased pressure on coastal ecosystems causing land degradation, deforestation and land use change. This review presents a comprehensive overview of existing research articles that apply spaceborne L‐band SAR data for geoscientific analyses that are relevant for coastal land applications