Mapping Blue and Red Color-Coated Steel Sheet Roof Buildings over China Using Sentinel-2A/B MSIL2A Images

Alim Samat,Jieqiong Luo,Wei Wang,Sicong Liu,Peijun Du,Erzhu Li,Jilili Abuduwaili,Paolo Gamba

doi:10.3390/rs14010230

Abstract

Accurate and efficiently updated information on color-coated steel sheet (CCSS) roof materials in urban areas is of great significance for understanding the potential impact, challenges, and issues of these materials on urban sustainable development, human health, and the environment. Thanks to the development of Earth observation technologies, remote sensing (RS) provides abundant data to identify and map CCSS materials with different colors in urban areas. However, existing studies are still quite challenging with regards to the data collection and processing costs, particularly in wide geographical areas. Combining free access high-resolution RS data and a cloud computing platform, i.e., Sentinel-2A/B data sets and Google Earth Engine (GEE), this study aims at CCSS material identification and mapping. Specifically, six novel spectral indexes that use Sentinel-2A/B MSIL2A data are proposed for blue and red CCSS material identification, namely the normalized difference blue building index (NDBBI), the normalized difference red building index NDRBI, the enhanced blue building index (EBBI), the enhanced red building index (ERBI), the logical blue building index (LBBI) and the logical red building index (LRBI). These indexes are qualitatively and quantitatively evaluated on a very large number of urban sites all over the P.R. China and compared with the state-of-the-art redness and blueness indexes (RI and BI, respectively). The results demonstrate that the proposed indexes, specifically the LRBI and LBBI, are highly effective in visual evaluation, clearly detecting and discriminating blue and red CCSS covers from other urban materials. Results show that urban areas from the northern parts of P.R. China have larger proportions of blue and red CCSS materials, and areas of blue and red CCSS material buildings are positively correlated with population and urban size at the provincial level across China.

Highlights

Over the last few decades, the Earth’s surface has experienced dramatic changes due, among other reasons, to rapid urbanization
To show the performance of normalized difference blue building index (NDBBI), normalizeddifference difference red building index (NDRBI), enhanced blue building index (EBBI), and enhanced red building index (ERBI) indexes for blue and red color-coated steel sheet (CCSS) roof enhancement, nine distinct sites with different landscape heterogeneity were selected from the Sentinel 2-A image captured on 15 October 2020 over Urumqi
While blue CCSS roofs, blue painted asphalt roads as shown by Figure 1b and highlighted with a green rectangle at the bottom of images in the fifth row, construction sites covered by blue nets highlighted with a green rectangle at the right edge of images in the seventh row, snow coverage and hill shadows as shown by the RGB image in the eighth row, are highlighted by NDBBI due to the spectral similarity, and even some water is highlighted by blueness index (BI) as shown by the sixth image in firth row, the contrast between blue CCSS roofs and the backgrounds is much higher in the EBBI

Summary

Introduction

Over the last few decades, the Earth’s surface has experienced dramatic changes due, among other reasons, to rapid urbanization. This process is expected to continue for the rest of the 21st century, for developing countries in Asia and Africa [1]. 0.60% of the global land surface, and by 2030 the number of the world urban population will swell to approximately 8.6 billion, more than 70% of the world population [2,3,4,5] Along with this trend of global urbanization, the global urban area is expected to increase by roughly 40–67% until 2050 relative to the base year of 2013, with a growth ratio of more than 200% by the year 2100 [1,6]. Urbanization is one of two major global environmental concerns of the 21st century [12,13], mainly because urban expansion has posed a wide range of challenges and issues to the socialeconomic, ecology, and environment at regional, national and global scales [1,6,14,15,16,17,18,19,20,21]

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