查看更多>>摘要：Urbanization is the second largest mega-trend right after climate change. Accurate measurements of urban morphological and demographic figures are at the core of many international endeavors to address issues of urbanization, such as the United Nations' call for "Sustainable Cities and Communities". In many countries - particularly developing countries -, however, this database does not yet exist. Here, we demonstrate a novel deep learning and big data analytics approach to fuse freely available global radar and multi-spectral satellite data, acquired by the Sentinel-1 and Sentinel-2 satellites. Via this approach, we created the first-ever global and quality controlled urban local climate zones classification covering all cities across the globe with a population greater than 300,000 and made it available to the community (https://doi.org/10.14459/2021mp1633461). Statistical analysis of the data quantifies a global inequality problem: approximately 40% of the area defined as compact or light/large low-rise accommodates about 60% of the total population, whereas approximately 30% of the area defined as sparsely built accommodates only about 10% of the total population. Beyond, patterns of urban morphology were discovered from the global classification map, confirming a morphologic relationship to the geographical region and related cultural heritage. We expect the open access of our dataset to encourage research on the global change process of urbanization, as a multidisciplinary crowd of researchers will use this baseline for spatial perspective in their work. In addition, it can serve as a unique dataset for stakeholders such as the United Nations to improve their spatial assessments of urbanization.
查看更多>>摘要：In 2021, coastal communities in the Sea of Marmara were impacted by large sea snot events. Based on data collected by several satellite sensors, we analyze and present the spectral reflectance characteristics of sea snots in the visible and near-infrared wavelengths. Sea snots often form elongated image slicks in Red-Green-Blue (RGB) or false-colour RGB (FRGB) images. Most reflectance spectra of sea snots show largely featureless spectral shapes, with continuous reflectance increases from the blue to the red, which then become flat toward the near infrared wavelengths. Some reflectance spectra show a local trough around 670 nm, indicating presence of chlorophyll a pigment, and thereby live algae. A 20-year time series of satellite data also reveals large-scale sea snot events in the Sea of Marmara before 2021. These results suggest that it might be possible to develop algorithms to search and map sea snots at a global scale, as sea snot events also occur in other regions. The results also indicate that remote differentiation of sea snots and marine debris using multi-band sensors may be difficult because of the spectral similarity between them.
NSTL
Elsevier