سنجش اثرات سبزينگي گياهي در تحولات فضايي شدت جزيره حرارتي سطح كلانشهر تهران با استفاده از تصاوير ماهواره اي LANDSAT8 و ASTER

Measuring the Impact of Vegetation Greenness on Spatial Changes of Heat Island Intensity in Tehran Metropolitan by Using ASTER and Landsat8 Satellite Images

حرارت سطح شهري (LST) متغير كليدي براي كنترل ارتباط بين شار حرارت تابشي، نهفته و محسوس مي باشد. بدين ترتيب تحليل و درك پويايي LST و شناسايي ارتباط آن با تغييرات منشاء انساني براي مدلسازي، پيش بيني تغييرات محيطي و نهايتا سياستگذاري شهري لازم است. از سمتي هم افزايش مقدار پوشش گياهي يكي از كاراترين استراتژيهاي كاهش اثرات خرده اقليم شهري مي باشد. در همين راستا جهت تحليل رونديابي تغييرات حرارتي سطوح و ميزان همبستگي فضايي سبزينگي پوشش گياهي با اين پديده در اثر تحولات شهرنشيني و شهرسازي شهر تهران بين سالهاي 94-1382 مورد پژوهش واقع شده است. تصاوير ماهواره اي بدون پوشش ابري و صاف كلانشهر تهران توسط ماهواره ي Landsat8 براي مرداد ماه سال 1394 و ماهواره ي ASTER براي مرداد ماه سال 1382 به كمك نرم افزار Envi و از طريق الگوريتم هاي مختلف در سنجش از دور به الگوهاي فضايي ميزان حرارت سطوح و شاخص پوشش گياهي نرمال شده (NDVI) كلانشهر تهران تبديل شده است. خروجي هاي فضايي اين پژوهش نشان مي دهند در طي تقريبا يك دهه ي اخير كمينه ي و ميانگين حرارت سطوح كلانشهري تهران به ترتيب c̊ 3.67 و c̊ 0.47 كاهش يافته است. همچنين ميانگين شاخص پوشش گياهي نرمال شده از0.06- به 0.10 افزايش يافته است. در همين بازه زماني برآورد همبستگي فضايي بين NDVI با LST در مناطق 22گانه شهر هم حاكي از كاهش 2% است. اين كاهش همبستگي به معناي افزايش نقش فعاليت هاي انساني بر ميزان شدت جزيره حرارتي شهر است. بنابراين توجه به برنامه ريزي فعاليت هاي انساني در شهر در راستاي جلوگيري از تغييرات اقليم در كلانشهري همچون تهران بيش از پيش جهت دستيابي به توسعه ي پايدار الزامي به نظر مي رسد.

The simplest definition of urbanization is that urbanization is the process of becoming urban. Urban climate is defined by specific climate conditions which differ from surrounding rural areas. Urban areas، for example، have higher temperatures than surrounding rural areas and weaker winds. Land Surface Temperature is an important phenomenon in global climate change. As the green house gases in the atmosphere increases، the LST will also increase. Energy and water exchanges at the biosphere–atmosphere interface have major influences on the Earth's weather and climate. Numerical models ranging from local to global scales must represent and predict effects of surface fluxes. The urban thermal environment is influenced by the physical characteristics of the land surface and by human socioeconomic activities. The thermal environment can be considered to be the most important indicator for representing the urban environment. Vegetation is another important component of the urban ecosystem that has been the subject of much basic and applied research. Urban vegetation influences the physical environment of cities through selective absorption and reflection of incident radiation and regulation of latent and sensible heat exchange Satellite-borne instruments can provide quantitative physical data at high spatial or temporal resolutions. Visible and near-infrared remote sensing systems have been used extensively to classify phenomena such as city growth، land use /cover changes، vegetation index and population statistics. Finally، we propose a model applying non-parametric regression to estimate future urban climate patterns using predicted Normalized Difference Vegetation Index and Heat Island Intensity. I conducted all spatial analysis in the UTM Zone 39 Northern Hemisphere projection. The fundamental procedure I used for evaluating change in land surface temperature was to relative temperature for both images، so that the values are temperature difference between the coldest and hottest areas in Tehran metropolitan. subtracting these images from each other results in relative temperature change from 2003 to 2015. Landsat satellite data were used to extract land use/land cover information and their changes for the abovementioned cities. Land surface temperature was retrieved from Landsat thermal images. The relationship between land surface temperature and landuse /land-cover classes، as well as the normalized vegetation index (NDVI) was analyzed. In this study، LST for Tehran metropolitan was derived using SW algorithm with the use of Landsat 8 Optical Land Imager (OLI) of 30 m resolution and Thermal Infrared Sensor (TIR) data of 100 m resolution. SW algorithm needs spectral radiance and emissivity of two TIR bands as input for deriving LST. The spectral radiance was estimated using TIR bands 10 and 11. Emissivity was derived with the help of land cover threshold technique for which OLI bands 2، 3، 4 and 5 were used. The output revealed that LST was high in the barren regions whereas it was low in the hilly regions because of vegetative cover. As the SW algorithm uses both the TIR bands (10 and 11) and OLI bands 2، 3، 4 and 5، the LST generated using them were more reliable and accurate. NDVI negatively affected LST and Urban Heat Island in vegetation areas in 2003 and 2015 in Tehran metropolitan. This analysis provides an effective tool in evaluating the environmental influences of zoning in urban ecosystems with remote sensing and geographical information systems. This method exhibits a promising performance in UHI forecast. The predicted LST confirms that urban growth has severely influenced UHI pattern through expanding the hot area. Our study confirmed that LST prediction performance is strongly depended on the resolution. The results reveal that the urban LST is affected mainly by the land surface characteristics and has a close relation to the abundance of vegetation greenness. The spatial distance from the UHI centre is another important factor influencing the LST in some areas. The methodology presented in this paper can be broadly applied in other metropolitans which exhibit a similar dynamic growth. Our findings can represent a useful tool for policy makers and the community awareness of environmental assessment by providing a scientific basis for sustainable urban planning and management. This provides an effective tool in evaluating the vegetation greenness of different zoning in urban ecosystems with remote sensing and geographical information systems. From the perspective of land use planning and urban management، it is recommend that planners and policy makers should pay serious attention to future land use policies that maintain a relevant proportion of public space، green areas، and land surface physical characteristics.