بررسي شيب دماي سطح زمين در ايران با داده هاي روزهنگام موديس

Analysis the slope of land surface temperature of Iran using MODIS data

آگاهي از دماي سطح زمين تغييرات زماني - مكاني ترازمندي انرژي در سطح زمين را آشكار مي سازد. در داده هاي دماي سطح زمين موديس اختلاف زمان خورشيدي محلي وجود دارد. اين اختلاف ممكن است به دليل تفاوت زماني در برداشت پيكسل هاي يك خط پيمايش ماهواره در يك روز باشد يا در روزهاي مختلف زمان محلي برداشت دما در يك پيكسل متغير باشد. هدف از پژوهش كنوني بررسي شيب دماي سطح زمين و تغييرات زماني - مكاني آن در ايران است كه با داده هاي روزهنگام موديس تِررا و آكوا بررسي شده است. از نتايج اين پژوهش ميتوان در برآورد دماي سطح زمين براي يك ساعت محلي ثابت استفاده كرد. بدين ترتيب، امكان مقايسه داده هاي دورسنجي دماي سطح زمين با داده هاي ايستگاهي و نيز امكان مقايسه دماي پيكسل هاي مختلف در سراسر ايران با يكديگر فراهم مي آيد. تغييرات زماني - مكاني چشم گيري در شيب دماي سطح زمين ايران ديده ميشود؛ اين تغييرات از شرايط محيطي و تغييرات دريافت انرژي خورشيد اثر مي پذيرد. در ماههاي مختلف سال شيبهاي دمايي صفر تا 1+ درجه كلوين بر ساعت و 1+ تا 2+ درجه كلوين بر ساعت گستره بيشتري از ايران را پوشش ميدهند؛ با اين حال، در دوره سرد سال شيب هاي صفر تا 1- درجه، به ويژه در بلندي هاي البرز و زاگرس، گسترش مي يابد.

Introduction: The MODIS facility for the Earth Observing System is a key element that supports ambitious goals related to studying the Earth as a system. One of the MODIS products is high quality land surface temperature data that product in Terra and Aqua platforms. Knowledge of the LST provides information on the temporal and spatial variations of the surface equilibrium state and is of fundamental importance in many applications. Therefore it is required for a wide variety of climatic, hydrological, ecological, and biogeochemical studies. Due to the intrinsic scanning characteristics of the MODIS instrument onboard the polar-orbiting satellites, the differences in local solar time for pixels along a given scan line on the same day or for the same pixel on different days in one revisit period may reach up to 2 hour. As LST changes with local solar time, it is therefore not possible to directly compare the LST of different pixels on the same day or of the same pixel on different days. Awareness about slope of land surface temperature is an important factor for cognition of land surface temperature behavior that can be used for increasing spatial and temporal resolution, comparability with other data, and accuracy achievement. The results will help to calculate a time consistent land surface temperature. Materials and methods: Land surface temperature data used in this researchare product using Normalized split windows algorithm. This data downloaded from MODIS website (http://reverb.echo.nasa.gov/reverb) in daily time scale for temporal range of 2002/07/08–2015/11/30. Prior to this date Aqua MODIS data is not available. This dataset contain measurements of land surface temperature, quality assurance, view time, view angel, land surface emissivity and is available for day time and night time. MODIS Terra 10:30AM and Aqua 1:30PM data used in this study. A matrix in dimensions of 4984*1884077 is provided from this dataset for Terra and Aqua day time land surface temperature and day view time thatprovidedbasic information for this study. The slope of land surface temperature between tow observation of Terra (10:30AM) and Aqua (1:30PM) is calculated. View time and land surface temperature measurements should first recall and calculate variation of land surface temperature in relation to observationtime distance between Terra/Aquameasurement for each pixel of Iran for every day of time series.Slope of land surface temperature calculated inmonthly long term meanfor spatial and temporal analysis. Results and discussion: View time is an important parameter in analysis of land surface temperature slope. View time distribution of land surface temperature in Iran show that Terra and Aqua view time has a high uniformity in frequency percent of observation times for land surface temperature at 10-12 and 12:30-14:30 for Terra and Aqua respectively. The coordination of land surface temperature slope and topography inIran is high. Low elevation lands between Zagros and central mountain ranges with northwest to southeast direction and central hollows such as Kavir plain, Lut desert and Jazmouryan is visible with higher slope in land surface temperature in alldifferent months of year. North and south shorelines and high elevations is the regions with smaller slope of land surface temperature. The slopes of less than 2 kelvin/hourin land surface temperature occurred in 85% of Iran territory. Difference between Terra and Aqua land surface temperature decreased clockwise from northeast aspects to southwest and increased from northwest to northeast.Slope of land surface temperature has an inverse relation with slope of land and decreased one kelvin/hour from zero to 22 degree slopes. Conclusion: Significant spatial and temporal variation that occurred in land surface temperature slope of Iran is the result of variation in environmental conditions and incoming solar radiation. Slope of land surface temperature in shorelines and mountainous regions is lower than deserts and low level elevations in all months of year. Slopes of zero to 1 and +1 to +2 kelvin/hour in land surface temperature covered great areas of Iran in different months. Zero to -1 kelvin/hour slope spread in winter season in high level elevations of Alborz and Zagros mountains. Decreasing of land surface temperature slope with increasing land slop can reflect relation between land surface temperature and elevation. The results show that small amounts of land surface temperature slop is the characteristic of major parts of Iran. In these conditions we can product a time consistent land surface temperature data for each pixels of every day in available time series for a time between MODIS Terra and Aqua observations.