بررسی ارتباط دمای سطح زمین با کاربری اراضی و شاخص اختلاف گیاهی نرمال‌شده در دشت گرگان

این تحقیق با هدف بررسی ارتباط دمای سطح زمین با پوشش گیاهی و کاربری اراضی دشت گرگان به کمک داده های سنجش از دور انجام شد. در گام نخست، تصویر لندست 8 متعلق به سال 2018، پیش پردازش و آماده گردید و نقشه کاربری/پوشش سرزمین در 8 طبقه تهیه شد. سپس، برای اندازه گیری دمای سطحی از باند حرارتی تصویر و معادلات مربوط استفاده گردید. سرانجام، از شاخص اختلاف گیاهی نرمال شده یا ndvi برای محاسبه گسیل مندی سطحی استفاده و نقشه دمای سطح زمین lst استخراج شد. به منظور خنثی کردن اثر ارتفاع بر lst، پیکسل های انتخابی از نقاط هم ارتفاع در هر کاربری انتخاب شدند. نتایج نشان داد کاربری بایر به دلیل نداشتن پوشش حفاظتی دارای دمای بیشتری (96/45 درجه سانتی گراد) است، درحالی که کاربری زراعت آبی (با بالاترین میزان سبزینگی) با دمای 03/34 درجه سانتی گراد کم ترین میانگین دمایی را در بین سایر کاربری ها داشت. از آنجاکه کاربری جنگل در ارتفاعات بالاتری قرار دارد، دمای سطحی آن بصورت جداگانه بررسی گردید. مقایسه دمای سطحی پیکسل های مربوط به کاربری جنگل و بخش جنگل تراشی شده نشان داد که میزان lst در بخش جنگل تراشی شده حدود 5 درجه سانتی گراد بیشتر از کاربری جنگل است. در مجموع، مناطقی که پوشش گیاهی متراکم تری مانند جنگل دارند میزان lst به مراتب کمتری از سایر کاربری ها داشتند.

Investigation the relationship between surface temperature and land use and Normalized Difference Vegetation Index in Gorgan plain

Introdsults and DiscussionThe results showed that bare land class has a higher temperature (45.96 ° C) due to lack of protective cover. Since the vegetation is very limited and dispersed in the bare land areas, the Earth is more exposed to solar waves. On the other hand, the surface of the bare solid ground is bright, which affects energy absorption and increases surface temperature. While the use of irrigated agriculture and water resources was 29.95 and 34.33 degrees Celsius, the lowest average temperature was observed among other classes. Considering the time taken to get the image of products cultivated in agriculture, they had an acceptable level of growth and greenness (high NDVI index highlighted the greenery of arable crops on this date) and by influencing evaporation reduction and maintaining soil moisture in effective thermal modification Which have led to less solar heat absorption and eventually reduced temperature. Water resources also reduce the surrounding air due to its high heat capacity and low solar energy absorption. Since forest class is at higher altitudes, its surface temperature was studied separately. The comparison of the surface temperature of the pixels related to the use of forest and the forestry sector showed that the LST in the forestry sector was about 5 degrees Celsius above the forest class.According to the results, the correlation between the NDVI index and the surface temperature is 0.65. The negative correlation obtained between this index and the surface temperature indicates an inverse relationship between this index and the surface temperature, and it can be deduced that in areas with high vegetation density such as forest use, surface temperature is much lower than other uses, which suggests a type of relationship Usage with surface temperature. According to Sig, this correlation is significant at 95% confidence level.Evaluation of surface temperature map prepared with ground dataThe results of the correlation test between the surface temperature of Landsat 8 and the air temperature of the meteorological station as well as the correlation between the air temperature and the existing stations were both obtained at 0.99, which confirmed the accuracy of equation (1) used to convert the LST data to the data Air temperature. The difference in LST between stations in the area indicates that stations are located in different environmental conditions due to environmental factors such as elevation, slope, direction, distance from the sea on LST.ConclusionIn this study, to determine the relationship between land use and LST, the surface temperature map of the area was prepared and the surface temperature of the area between 14 and 51 degrees Celsius was estimated. Since the height parameter has an effective effect on temperature, the samples were selected from the height points of each land use. Thus, the effect of height factor on the results of the research was neutralized. In areas where vegetation is dense, such as forest, surface temperatures are far lower than other uses. Also, the irrigated agriculture class, which had a higher density than rangelands, showed lower temperatures. On the other hand, the bare lands had the highest surface temperature. Therefore, it can be concluded that vegetation is a major factor in surface temperature, especially in areas where this coating is denser. The effect is more obvious.