نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه جغرافیای طبیعی، دانشکده علوم زمین، دانشگاه شهید بهشتی، تهران، ایران

2 گروه جغرافیای طبیعی، دانشکده علوم انسانی، دانشگاه تربیت مدرس، تهران، ایران

چکیده

 سابقه و هدف:
آشکارسازی تغییر، فرایندی برای یافتن منطقه­ های متناقض در تصویر­های زمانی متفاوت از ناحیه‌ای مشابه می‌باشد. پوشش گیاهی در جذب دوده‌ها و سرب هوا ، جلوگیری از پخش مواد آلاینده در محیط‌های شهری و کمک به پاک‌سازی هوا و کاهش جزایر حرارتی،بسیار موثر است. بررسی کاهش یا افزایش پوشش گیاهی در تهران بعنوان کلان‌شهر و نیز شهرستان‌های حومه آن، با توجه به رشد بی‌رویه جمعیت و ساخت‌وساز به شدت ضرورت دارد. هدف از این پژوهش بررسی روند تغییر­های زمانی-مکانی پوشش گیاهی در تهران و اقمار و رابطه آن با دما در دوره‌های زمانی مختلف می‌باشد. نتایج این تحقیق می‌تواند در مطالعات مربوط به زیست پذیری شهری، کاهش اثر­های سوء جزایر حرارتی شهری و علوم محیطی مؤثر واقع شود. 
مواد و روش‌ها:
ابتدا استخراج و آماده سازی داده‌های تصاویر از طریق سنجنده+ ETM ماهواره لندست 7 در سال‌های 2001 تا 2015 انجام و ماه ژوئن بعنوان گرم‌ترین ماه منطقه مورد مطالعه انتخاب شد. سپس گزینش روزهای مورد بررسی و انجام تصحیحات تصاویر و تهیه نقشه‌های LULC و ترسیم نمودار درصد مساحت منطقه ­ها مورد توجه قرار گرفت. محاسبه شاخص‌های پوشش گیاهی و منطقه­ های ساخته‌شده و محاسبه دمای سطح زمین همراه با ارزیابی صحت داده‌های دمای سطح زمین از مرحله­ های دیگر روش تحقیق بود. در نهایت ترسیم نمودار درصد مساحت هر شاخص و نیز ترسیم نمودار پراکنش و تابع گوسی با بررسی دگرگونی مکانی پوشش گیاهی انجام پذیرفت.
نتایج و بحث:
با توجه به نقشه کاربری زمین­ ها و پوشش زمین(LULC)،  برای سال‌های 2001، 2005، 2010 و 2015 افزایش پوشش گیاهی در سال 2015 نسبت به دوره‌های قبل در منطقه مورد مطالعه مشهود است. رشد منطقه ­های ساخته‌شده در غرب منطقه به خوبی دیده می‌شود. در نمودار درصد مساحت هر کلاس کاربری زمین­ ها و تغییر آن در 4 سال منتخب، از سال 2001 درصد پوشش گیاهی روبه کاهش رفته که تا سال 2005 و 2010 ادامه داشته، و در سال 2015 افزایش چشمگیر یافته است. از سوی دیگر روابط بین دمای سطحی و شاخص‌های NDVI و SAVI خطی نبوده و بر اساس برازش معادلات آماری در هر وضعیت، عامل­ های دیگری در کاهش یا افزایش LST نقش دارند. در نمودار تابع چگالی نرمال، تغییر­های شاخص NDVI در دوره دوم و سوم مشابه یکدیگر بوده و در این دو دوره نسبت به دوره اول، میانگین افزایش‌ و همچنین با توجه به کاهش واریانس، ارتفاع منحنی افزایش‌یافته است. در تحقیق حاضر و با بررسی تهران و اقمار، کاهش میزان LST در دوره دوم و سوم یعنی از 2006 تا 2015 مشاهده می‌شود. از سوی دیگر مساحت پوشش گیاهی بطور کلی در منطقه روبه افزایش است. از جنبه مکانی و مطابق بررسی‌های انجام‌شده، تهران بیشترین درصد کلاس یک NDVI یعنی سطح­های بدون پوشش گیاهی را به خود اختصاص داده است.
نتیجه‌گیری:
با توجه به بررسی شاخص‌های NDVI، SAVI و NDBI، روند کلی مساحت پوشش گیاهی در منطقه مورد مطالعه در حال افزایش است. با درنظرگرفتن مقادیر 15R2"> ، پوشش گیاهی در شهرستان ری در حال نابودی می‌باشد. در شهرستان‌های رباط‌کریم و تهران سطح­ های پوشش گیاهی در حال افزایش است. رشد افسارگسیخته شهرک‌های اقماری در حومه تهران موجب تخصیص زمین‌های بایر و مزرعه ­ها و پوشش گیاهی به ناحیه­ های ساختمانی و مسکونی شده است که این امر جزایر حرارتی و شرایط نامساعد زندگی را تشدید می‌کند.

کلیدواژه‌ها

عنوان مقاله [English]

Detection of spatio-temporal changes in the vegetation of Tehran and satellite cities in association with land surface temperature

نویسندگان [English]

  • Mahmoud Ahmadi 1
  • Zahra Alibakhshi 1
  • Manouchehr Farajzade Asl 2

1 Department of Natural Geography, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

2 Department of Natural Geography, Faculty of Humanities Sciences, Tarbiat Modares, Tehran, Iran

چکیده [English]

Introduction:
Change detection is a process to find the paradoxical regions in different temporal imageries of a similar area. Vegetation is very effective at the absorption of grime and lead, prevention of the spread of contaminations in urban environments, clearing the air, and reduction of heat islands. The need to investigate the decrease or increase in vegetation is extremely important in Tehran as a metropolis, as well as its satellite counties because of the increase in population and construction. The purpose of this research was to investigate the spatiotemporal changes in the vegetation of Tehran and its satellite cities in association with temperature during different temporal periods. The results of this research can be useful in studies concerning urban viability, reducing the effects of urban heat islands, and environmental sciences.
Material and methods:
Initially, the extraction and preparation of data were carried out using the ETM+ sensor of Landsat 7 satellite from 2001 to 2015, with June being selected as the hottest month of the study area. Then, the selection of days to be studied and correcting imagery, preparing LULC maps and plotting the area percentage was done. The computation of vegetation indices and built-up areas and the calculation of land surface temperature along with the assessment of the accuracy of surface temperature data were other stages of the research methodology. Finally, the area percentage of each index, as well as the scatter plot and Gaussian function chart were produced and the spatial variation of vegetation was studied.
Results and discussion:
According to the land use and land cover map (LULC) in 2001, 2005, 2010, and 2015, the vegetation significantly increased in 2015 compared to previous courses. The development of the residential area in the west region was higher than in other regions. In the charts of the area percentage for each land use class and its change over the four selected years, the vegetation percentage has been decreased since 2001, which continued in 2010 and 2015. In this study, the relationships between surface temperature and NDVI and SAVI indices were not linear, which showed that there is another controlling factor. In the normal density function chart, which is usually described by mean and standard deviation, variations of NDVI and SAVI indices were similar in the second and third periods, and the mean increased in these two periods compared to the first period, and the height of curve increased due to the reduction of variance. In this study, the results showed a decrease in the value of LST in the second and third periods from 2006 to 2015. On the other hand, the vegetation area was increasing in the region. From a spatial point of view, Tehran has the highest percentage of class one of NDVI that have no vegetation surfaces. 
Conclusion:
Regarding the study of NDVI, SAVI and NDBI indices, the overall trend of vegetation cover in the study area was increasing. Considering the values of 15R2"> , the vegetation in Ray County was defunct. In the cities of Robat Karim and Tehran, vegetation cover was increasing. The high growth of satellite towns in the surroundings of Tehran has led to the allocation of land and fields and vegetation to residential areas, which exacerbate the heat islands and the unfavorable conditions of life.

کلیدواژه‌ها [English]

  • vegetation
  • Spatio-temporal changes
  • Tehran
  • Land Surface Temperature

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