北京城区道路系统路网空间特征及其与LST和NDVI的相关性

城市道路系统是人类活动最为频繁的场所之一,研究路网空间特征与相关环境指标的关系,可为定量分析城市建设过程对城市生态环境的影响以及为城市基础设施规划管理提供方法。对北京市五环内各级道路抽样调查及面向对象的高分辨率遥感影像识别,建立道路空间信息数据库,运用TM影像反演获得地表温度(LST)及归一化植被指数(NDVI),研究4种不同分析网格下城市路网特征与两者的空间相关性。结果表明,在较大分析网格下(4×4),路网空间指标与LST mean及NDVI mean相关性显著;中等网格下,除LST与NDVI的平均值外,路网空间指标还可与两者最小值建立相关性;在较小窗口下(32×32),除平均值与最小值,还可建立特定道路指标与LST max及NDVI max的联系;各路网指标中,单位面积道路总长与LST及NDVI相关性最强;加权道路结点数在8×8和32×32网格分析中,与NDVI的相关性高于该指标未加权值,而结点指标均不适合与LST max建立联系;在各分析网格下,4项道路指标均与NDVI mean呈极显著负相关,表明道路绿地建设规模还不足以对NDVI的强度及分布产生较大影响。

Spatial features of road network in Beijing built up area and its relations with LST and NDVI

The rapid urbanization process has greatly changed the spatial pattern of cities, especially artificial facilities. As an important municipal infrastructure, urban road systems occupy more than 1/4 of the built-up area. It supports an open space for material flow, energy flow and information flow, and its developing speed and distribution are far ahead of other urban infrastructure. Urban roads are also a kind of typical impervious surface. Compared with natural green space, the building materials like cement and asphalt make urban road system a different thermal characteristic, and in terms of spatial distribution, those traits may eventually result in the significant impact on the pattern of urban thermal environment. Many studies involved in urban underlying surfaces and their relationship with urban heat island (UHI), while the relationship between the spatial structure of urban roads and UHI has not been reported. More information about the interactive impact between the spatial structure of urban roads and urban environment needed to be quantitatively assessed during the process of rapid urbanization, which could provide some scientific guidance for urban infrastructure planning and management toward a sound and eco-friendly development. In this paper, through field survey (by using Laser distance meters and GPS to collect valid information from different sections of 238 roads within the study area) and high resolution remote sensing data (Quick Bird data source) recognition based on the object-oriented method, a spatial database of urban roads within 5^th ring road Beijing was established, which included the length, width and intersection nodes of different classes of urban roads. A thermal infrared inversion of Landsat TM was conducted for retrieving LST and NDVI,which are the two common indicators to characterize thermal environment and vegetation information. Then a correlation analysis between the road system characteristics and LST and NDVI was carried out. The results showed that there was a significant correlation among parameters of road system, LST_mean and NDVI_mean in larger grids (4×4). Meanwhile, LST_min and NDVI_min were related with parameters of road net in moderate grids (8×8, 16×16). In terms of small grid (32×32), besides the mean and maximum value of LST and NDVI, the correlations were observed between certain road indicators and LST_max and NDVI_max; The total length of roads is the best variable described the change of LST and NDVI among all the parameters. When the number of nodes was weighted for area, the correlation coefficients with NDVI in 8×8 and 32×32 grids were increased. At all levels of analysis grids, all four road indicators presented a significantly negative correlation with NDVI_mean, which implied that the area of urban road green space was too small to play an important roles on the intensity and spatial distribution of NDVI. The factual of linkages among various spatial attributes of urban road networks to the intensity, quantity, and distribution of LST and NDVI may help develop a new approach to quickly identify the overall UHI spatial patterns and further study the relations between urban thermal environments and human activities.