In the last few decades, thousands of satellites have been launched into space by humanity. These satellites serve various purposes, from taking pictures and mapping the Earth to improving GPS technology in our phones. One type of satellite equipped with specialized scientific instruments is the Synthetic Aperture Radar (SAR) satellite.
SAR satellites work by emitting a radar pulse and then measuring the reflection or backscatter, which depends on physical properties like height, roughness, or structure. Unlike other satellites, SAR is effective in all weather conditions. However, SAR data comes with limitations such as signal noise and image distortion, making data interpretation challenging, especially in urban studies.
Most urban monitoring efforts rely on optical images, providing clear two-dimensional views of surface changes but lacking the crucial three-dimensional aspects needed for comprehensive urban analysis. To address this issue, researchers have combined SAR and optical data to reconstruct long-term backscatter coefficient data over three decades (1990 through 2022) in the Jing-Jin-Ji region of China.
The research team, led by Xuecao Li from China Agricultural University, used Sentinel-1 Ground Range Detected data, long-term Landsat images, and ALOS World 3D data to map urban growth and changes in the Jing-Jin-Ji region, which includes major cities like Beijing and Tianjin. The study revealed significant urban expansion and building height changes, with Beijing experiencing rapid vertical growth while other cities like Cangzhou showed slower growth rates.
Apart from estimating building heights, the researchers used the long-term data for urban surface classification and flood monitoring. This data is crucial for urban planners and policymakers to make informed decisions. The team aims to expand the approach globally and analyze more urban parameters for sustainable development goals.
The findings of this study, published in the Journal of Remote Sensing, open up opportunities for further research in urban environmental issues related to urban heat islands, dynamic building heights, and carbon emissions. By utilizing SAR and optical data, researchers can gain valuable insights into urban dynamics and contribute to achieving sustainable development objectives.