Satellite-measured growth of the urban heat island of Houston, Texas

Growth of the surface temperature urban heat island (UHI) of Houston, TX is determined by comparing two sets of heat island measurements taken 12 years apart. Individual heat island characteristics are calculated from radiative temperature maps obtained using the split-window infrared channels of the Advanced Very High Resolution Radiometer (AVHRR) on board National Oceanic and Atmospheric Administration polar-orbiting satellites. Eighty-two nighttime scenes taken between 1985 and 1987 are compared to 125 nighttime scenes taken between 1999 and 2001. Analysis of the UHI characteristics from these two intervals reveals a mean growth in magnitude of 0.8 K, or 35%. The growth of the mean area of the UHI is found to range between 170 and 650 km², or from 38% to 88%, depending on the method of analysis.     

Comparison of impervious surface area and normalized difference vegetation index as indicators of surface urban heat island effects in Landsat imagery

This paper compares the normalized difference vegetation index (NDVI) and percent impervious surface as indicators of surface urban heat island effects in Landsat imagery by investigating the relationships between the land surface temperature (LST), percent impervious surface area (%ISA), and the NDVI. Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) data were used to estimate the LST from four different seasons for the Twin Cities, Minnesota, metropolitan area. A map of percent impervious surface with a standard error of 7.95% was generated using a normalized spectral mixture analysis of July 2002 Landsat TM imagery. Our analysis indicates there is a strong linear relationship between LST and percent impervious surface for all seasons, whereas the relationship between LST and NDVI is much less strong and varies by season. This result suggests percent impervious surface provides a complementary metric to the traditionally applied NDVI for analyzing LST quantitatively over the seasons for surface urban heat island studies using thermal infrared remote sensing in an urbanized environment.     

Assessments of urban growth in the Tampa Bay watershed using remote sensing data

Urban development has expanded rapidly in the Tampa Bay area of west-central Florida over the past century. A major effect associated with this population trend is transformation of the landscape from natural cover types to increasingly impervious urban land. This research utilizes an innovative approach for mapping urban extent and its changes through determining impervious surfaces from Landsat satellite remote sensing data. By 2002, areas with subpixel impervious surface greater than 10% accounted for approximately 1800 km², or 27 percent of the total watershed area. The impervious surface area increases approximately three-fold from 1991 to 2002. The resulting imperviousness data are used with a defined suite of geospatial data sets to simulate historical urban development and predict future urban and suburban extent, density, and growth patterns using SLEUTH model. Also examined is the increasingly important influence that urbanization and its associated imperviousness extent have on the individual drainage basins of the Tampa Bay watershed.     

Estimation of land surface temperature-vegetation abundance relationship for urban heat island studies

Remote sensing of urban heat islands (UHIs) has traditionally used the Normalized Difference Vegetation Index (NDVI) as the indicator of vegetation abundance to estimate the land surface temperature (LST)-vegetation relationship. This study investigates the applicability of vegetation fraction derived from a spectral mixture model as an alternative indicator of vegetation abundance. This is based on examination of a Landsat Enhanced Thematic Mapper Plus (ETM+) image of Indianapolis City, IN, USA, acquired on June 22, 2002. The transformed ETM+ image was unmixed into three fraction images (green vegetation, dry soil, and shade) with a constrained least-square solution. These fraction images were then used for land cover classification based on a hybrid classification procedure that combined maximum likelihood and decision tree algorithms. Results demonstrate that LST possessed a slightly stronger negative correlation with the unmixed vegetation fraction than with NDVI for all land cover types across the spatial resolution (30 to 960 m). Correlations reached their strongest at the 120-m resolution, which is believed to be the operational scale of LST, NDVI, and vegetation fraction images. Fractal analysis of image texture shows that the complexity of these images increased initially with pixel aggregation and peaked around 120 m, but decreased with further aggregation. The spatial variability of texture in LST was positively correlated with those in NDVI and in vegetation fraction. The interplay between thermal and vegetation dynamics in the context of different land cover types leads to the variations in spectral radiance and texture in LST. These variations are also present in the other imagery, and are responsible for the spatial patterns of urban heat islands. It is suggested that the areal measure of vegetation abundance by unmixed vegetation fraction has a more direct correspondence with the radiative, thermal, and moisture properties of the Earth's surface that determine LST.     

An analysis of urban thermal characteristics and associated land cover in Tampa Bay and Las Vegas using Landsat satellite data

Remote sensing data from both Landsat 5 and Landsat 7 systems were utilized to assess urban area thermal characteristics in Tampa Bay watershed of west-central Florida, and the Las Vegas valley of southern Nevada. To quantitatively determine urban land use extents and development densities, sub-pixel impervious surface areas were mapped for both areas. The urban-rural boundaries and urban development densities were defined by selecting certain imperviousness threshold values and Landsat thermal bands were used to investigate urban surface thermal patterns. Analysis results suggest that urban surface thermal characteristics and patterns can be identified through qualitatively based urban land use and development density data. Results show the urban area of the Tampa Bay watershed has a daytime heating effect (heat-source), whereas the urban surface in Las Vegas has a daytime cooling effect (heat-sink). These thermal effects strongly correlated with urban development densities where higher percent imperviousness is usually associated with higher surface temperature. Using vegetation canopy coverage information, the spatial and temporal distributions of urban impervious surface and associated thermal characteristics are demonstrated to be very useful sources in quantifying urban land use, development intensity, and urban thermal patterns.     

Remote sensing image-based analysis of the relationship between urban heat island and land use/cover changes

Global warming has obtained more and more attention because the global mean surface temperature has increased since the late 19th century. As more than 50% of the human population lives in cities, urbanization has become an important contributor for global warming. Pearl River Delta (PRD) in Guangdong Province, southern China, is one of the regions experiencing rapid urbanization that has resulted in remarkable Urban Heat Island (UHI) effect, which will be sure to influence the regional climate, environment, and socio-economic development. In this study, Landsat TM and ETM+ images from 1990 to 2000 in the PRD were selected to retrieve the brightness temperatures and land use/cover types. A new index, Normalized Difference Bareness Index (NDBaI), was proposed to extract bare land from the satellite images. Additionally, Shenzhen, which has experienced the fastest urbanization in Guangdong Province, was taken as an example to analyze the temperature distribution and changes within a large city as its size expanded in the past decade. Results show that the UHI effect has become more prominent in areas of rapid urbanization in the PRD region. The spatial distribution of heat islands has been changed from a mixed pattern, where bare land, semi-bare land and land under development were warmer than other surface types, to extensive UHI. Our analysis showed that higher temperature in the UHI was located with a scattered pattern, which was related to certain land-cover types. In order to analyze the relationship between UHI and land-cover changes, this study attempted to employ a quantitative approach in exploring the relationship between temperature and several indices, including the Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Normalized Difference Bareness Index (NDBaI) and Normalized Difference Build-up Index (NDBI). It was found that correlations between NDVI, NDWI, NDBaI and temperature are negative when NDVI is limited in range, but positive correlation is shown between NDBI and temperature.     

Remote Sensing Monitoring and Spatiotemporal Pattern of Land Use/Cover Change in Built-up Area of Tianjin in the Past 70 Years

Urban land use/cover changes have an important impact on urban ecosystem services functions and the environmental quality of human settlements. This study mapped urban expansion process using the historical data, remote sensing images and urban planning maps, and acquired the urban impervious surface and green space fraction based on big data platform. We analyzed the process of Tianjin urban expansion rate, intensity and urban land cover change since 1949, and revealed the driving factors in the process of urban expansion with social economic and policy factors. The results showed that the built-up area increased from 49.15 km² in 1949 to 663.39 km² in 2015. The expansion has undergone four stages of "acceleration – deceleration – acceleration - deceleration"; the urban expansion mode presents the filled with built-up area and along with the neighboring transportation trunk lines. The proportion of green space in the built-up area is increasing, indicating that the urban ecological greening in the main urban area of Tianjin has been improved.     

一带一路沿海超大城市热岛时空特征遥感分析

城市热岛不仅影响城市局地及区域气候,而且对城市空气质量、能源消耗、居民健康等有显著的负面作用。利用长时序遥感数据,系统地分析各超大城市热岛的时空特征,能够为城市热岛效应减缓政策的制定提供参考,对带路城市可持续发展具有重要意义。基于2001~2017年MODIS地表温度产品和Landsat土地利用分类数据,以城市热岛强度（Surface Urban Heat Island Intensity, SUHII）作为指标,从季节和年际的角度分析一带一路沿海超大城市2001~2017年热岛效应时空格局的变化。研究结果表明：①2001~2017年期间各超大城市的核心区存在扩张趋势,高强度热岛主要分布在人口活动密集的城市核心区;②年均城市热岛强度最大的城市是卡拉奇,多年SUHII平均值为3.02 ℃,热岛强度显著上升的是金奈（0.07 ℃/a,P<0.1）;③各城市热岛强度存在季节性差异,其中夏季城市热岛强度最大的城市是伊斯坦布尔,SUHII平均值为2.88 ℃,冬季城市热岛强度最大的城市是卡拉奇,SUHII平均值为4.45 ℃。     

Spatiotemporal Pattern of Urban-rural Aradient Land Cover Changes and Their Impact on Urban Heat Island in Xi′an City Since the 21st Century

Rapid urban expansion had a significant impact in land use/cover change along urban-rural gradient, and the increase of impervious construction land and the reduction of vegetation cover had induced and aggravated the urban heat island effect. Studying the impact of urban-rural gradient land cover change on urban heat island effect was significant for urban planning and construction, improving the comfort of human settlements and enhancing the function of urban ecological services. The surface temperature of Xi'an city was retrieved by mono-window algorithm based on Landsat images, and the thermal field intensity map was obtained by calculating the thermal field variation index, and the gradient land cover changes in urban and rural areas were analyzed with land use data. The results showed that: ①The urban heat island effect in Xi'an showed a trend of first increasing and then decreasing from 2000 to 2015. In 2000, the extremely strong heat island effect area accounted for 10.58% of the research area, and gradually increased to 16.14% in 2011, and then decreased to 9.00% in 2015. ②From 2000 to 2015, the area of construction land increased 412.76 km² and the intensity of extremely strong heat island expanded year by year with the expansion of urban built-up areas. ③About 70% of the non-heat island effect areas were located on farmland and forest land, and the proportion of water area in the non-heat island effect was increasing year by year from 31% to 47%, which showed that the increase of vegetation and water area could effectively alleviate the urban heat island effect.     

城市不透水面及其与城市热岛的关系研究-以泉州市区为例

利用Landsat TM卫星影像提取了泉州市1989到1996年的城市建成区不透水面,并研究了其与城市热岛之间的关系。根据Ridd(1995)提出的城市建成区不透水面与植被覆盖度有很强的负相关关系的思想,先利用归一化植被指数求出泉州市建成区的植被覆盖度,进而提取了泉州市建成区的不透水面。通过比较所提取的两个时相不透水面信息,可以看出泉州市区不透水面的面积在7年里有了明显的增加,并主要沿研究区东南部扩展。通过将所提取的不透水面信息与利用TM6波段反演的地表温度进行相关分析,可发现二者之间存在着明显的正相关关系。     

High-resolution urban thermal sharpener (HUTS)

A high resolution urban thermal sharpener (HUTS) was developed that increases the resolution of thermal infrared (TIR) data to that of visible and near infrared (VNIR) data by fitting the relationship between radiometric surface temperature, normalized difference vegetation index (NDVI) and surface albedo (α). HUTS was applied to TIR data aggregated to 90 m to represent a satellite acquired dataset and validated against the measured 10 m data from an aircraft over San Juan, Puerto Rico. HUTS sharpening reduced the root mean square error of surface temperature at the high resolution by 17% compared to no sharpening and outperformed other sharpening methods. HUTS is proposed as a useful tool to study urban meteorology and climatology at the microscale using ASTER satellite data.     

Validation of satellite observed thermal emission with in-situ measurements over an urban surface

The Basel Urban Boundary Layer Experiment (BUBBLE) is a joint European research project under the umbrella of COST (Coopération Européenne dans la domaine de la recherche Scientifique et Technique, COST 715: Meteorology applied to urban pollution problems). Besides very detailed field measurements of the structure and dynamics of the urban boundary layer, a series of satellite data has been analyzed and validated. Satellite data from MODIS, NOAA-AVHRR (14, 15, and 16) and Landsat-ETM were used and recorded during June and July 2002 in parallel to the BUBBLE field campaign. MODIS and NOAA-AVHRR data represent day and nighttime surface radiation temperatures in 930 m and 1100 m grid size. Landsat-ETM offers a unique resolution on 60 m, but with only daytime imagery at about the same time of MODIS overpass is available. This enables the validation of satellite measurements from different sensors with ground measurements at locations with various degrees of spatial homogeneity/heterogeneity (urban/rural land use). Several different algorithms for NOAA-AVHRR data were compared with in-situ measurements. The results show a very high correlation of the long wave emissions measured by the satellite with the in-situ measurements showing an accuracy of ± 3% to 5% on average, even in urban environments.     

21世纪以来西安城乡梯度土地覆盖变化及对城市热岛影响时空特征

城市快速扩张导致城乡梯度土地覆盖发生显著的变化,引发不透水地表的增加,植被覆盖的减少,从而加剧了城市热岛强度。研究城乡梯度土地覆盖变化引起的城市热岛效应,并揭示城市热岛的时空特征及强度的变化,对城市规划建设、人居环境改善及提升城市生态系统服务功能具有重要的意义。基于Landsat系列4期影像,利用单窗算法反演西安市地表温度,计算热场变异指数得到热力场强度图并对其进行等级划分,结合土地利用/覆盖类型数据分析城乡梯度土地覆盖变化对城市热岛强度的影响。结果表明：①2000年西安市极强热岛效应区占研究区面积的10.58%,逐渐增加到2011年极强热岛效应区域的面积占比达到16.14%,而后到2015年降低为9.00%,整体上西安市城市热岛效应呈现出了先增长后降低的趋势;②2000年到2015年城乡建设用地面积增加了412.76 km2,极强热岛强度的范围随城市建成区的扩张逐年向外扩展;③无热岛效应区约70%位于耕地和林地,水域在无热岛效应中的占比也在逐年增多,从31%增加到了47%。不透水地表面积占比与地表温度有显著相关性,城乡梯度植被和水体面积的增加可以有效地缓解城市热岛强度。     

Exploring indicators for quantifying surface urban heat islands of European cities with MODIS land surface temperatures

The term urban heat island describes the phenomenon of altered temperatures in urban areas compared to their rural hinterlands. A surface urban heat island encompasses the patterns of land surface temperatures in urban areas. The classical indicator to describe a surface urban heat island is the difference between urban and rural surface temperatures. However, several other indicators for this purpose have been suggested in the literature. In this study, we compared the eleven different indicators for quantifying surface urban heat islands that were most frequently used in recent publications on remote sensing-based urban heat island assessments. The dataset used here consists of 263 European cities with monthly mean temperatures from MODIS data products for July 2002, January 2003 and July 2003. We found that (i) the indicators individually reveal diurnal and seasonal patterns but show rather low correlations over time, and (ii) for single points in time, the different indicators show only weak correlations, although they are supposed to quantify the same phenomenon. Differentiating cities according to thermal climate zones increased the relationships between the indicators. Thus, we can identify temporal aspects and indicator selection as important factors determining the estimation of urban heat islands. We conclude that research should take into account the differences and instabilities of the indicators chosen for quantifying surface urban heat islands and should use several indicators in parallel for describing the surface urban heat island of a city.     

南京市热岛效应时空特征的遥感分析

城市热岛效应是城市化对城市气候影响最典型的表现, 不同城市由于其城市化水平、城市性质、规模以及自然条件的不同而具有不同的时空特征。利用高空间分辨率的Landsat TM 和高时间分辨率的MODIS 相结合定量地分析了南京市热岛效应的时空特征, 并探讨了遥感尺度对城市热岛效应时空特征的影响。结果表明: 南京市热岛效应日特征为白天大于夜晚; 季节特征从热岛强度和热岛范围两方面来说明, 热岛强度: 秋季> 夏季> 春季> 冬季, 分布范围: 夏季> 秋季> 春季> 冬季; 空间上存在3 个分布广且连续的强热岛区, 最大的热岛呈组团状分布、第二的呈线状分布、第三的热岛呈带状分布; 不同遥感尺度下观测到的城市热岛效应强度和范围不同。     

不同地表参数变化的上海市热岛效应时空分析

研究地表参数变化与热岛效应的关系对优化城市功能分区以及城市可持续发展具有重要意义。采用上海市2000、2005、2009年3个时期的Landsat ETM+卫星遥感影像,使用归一化不透水面指数(NDISI)、基于指数的植被指数(IVI)、归一化差异水体指数(MNDWI)分别从遥感影像中提取不透水面、植被和水体;然后从时间、空间角度并采用回归分析方法分析了上海市地表参数在这9 a中发生的变化及其对城市热环境造成的影响。结果表明:9 a中城市不透水面面积大幅增加,不透水面增加的代价是植被和水体大范围减少,形成了城市的热岛。上海市整体热岛强度是先增强后缓慢减弱的趋势,且热岛分布从集中型向分散型发展。     

Impacts of landscape structure on surface urban heat islands: A case study of Shanghai, China

Urbanization is taking place at an unprecedented rate around the world, particularly in China in the past few decades. One of the key impacts of rapid urbanization on the environment is the effect of urban heat island (UHI). Understanding the effects of landscape pattern on UHI is crucial for improving the ecology and sustainability of cities. This study investigated how landscape composition and configuration would affect UHI in the Shanghai metropolitan region of China, based on the analysis of land surface temperature (LST) in relation to normalized difference vegetation index (NDVI), vegetation fraction (Fv), and percent impervious surface area (ISA). Two Landsat ETM+ images acquired on March 13 and July 2, 2001 were used to estimate LST, Fv, and percent ISA. Landscape metrics were calculated from a high spatial resolution (2.5 × 2.5 m) land-cover/land-use map. Our results have showed that, although there are significant variations in LST at a given fraction of vegetation or impervious surface on a per-pixel basis, NDVI, Fv, and percent ISA are all good predictors of LST on the regional scale. There is a strong negative linear relationship between LST and positive NDVI over the region. Similar but stronger negative linear relationship exists between LST and Fv. Urban vegetation could mitigate the surface UHI better in summer than in early spring. A strong positive relationship exists between mean LST and percent ISA. The residential land is the biggest contributor to UHI, followed by industrial land. Although industrial land has the highest LST, it has limited contribution to the overall surface UHI due to its small spatial extend in Shanghai. Among the residential land-uses, areas with low- to-middle-rise buildings and low vegetation cover have much high temperatures than areas with high-rise buildings or areas with high vegetation cover. A strong correlation between the mean LST and landscape metrics indicates that urban landscape configuration also influences the surface UHI. These findings are helpful for understanding urban ecology as well as land use planning to minimize the potential environmental impacts of urbanization.     

Evaluating environmental influences of zoning in urban ecosystems with remote sensing

The influence of zoning on Normalized Difference Vegetation Index (NDVI) and radiant surface temperature (T_s) measurements is investigated in the City of Indianapolis, IN, USA using data collected by the Enhanced Thematic Mapper Plus (ETM+) remote sensing system. Analysis of variance indicates statistically significant differences in mean T_s and NDVI values associated with different types of zoning. Multiple comparisons of mean T_s and NDVI values associated with specific pairings of individual zoning categories are also shown to be significantly different. An inverse relationship between T_s and NDVI was observed across the city as a whole and within all but one zoning category. A range of environmental influences on sensible heat flux and urban vegetation was detected both within and between individual zoning categories. Examples for implementing these findings in urban planning applications to find examples of high and low impact development are demonstrated.     

基于遥感的长沙市城市热岛效应时空分析

利用TM/ETM+数据,以长沙市为例,反演了地表温度,并针对不同时相的遥感数据,利用城市热岛强度来反映热岛效应强弱的变化。结果表明,长沙市的热岛空间分布与城市建成区的轮廓相吻合。城市热岛的范围随着城市建设、新建开发区以及道路交通网的发展不断增大,且在东南方向为主要增长方向。根据热岛强度鉴别并提取了强热岛区与正常区,发现长沙市强热岛区的面积已经从1993年的13.18km2扩大至2008年的68.16km2。最后,对长沙市热岛未来的发展趋势进行了预测。