پايش تغييرات ماهانه و فصلي گاز متان با استفاده از داده‏هاي ماهواره GOSAT

Monitoring of Monthly and Seasonal Methane Amplitude in Iran using GOSAT Data

تغيير اقليم و گرمايش جهاني يكي از بزرگ‏ترين چالش‏هاي قرن حاضر معرفي شده است. گاز متان، به منزله يكي از مهم‏ترين گازهاي گلخانه‏اي، به‏تنهايي مسيول بيش از 18 درصد از گرمايش ناشي از انتشار گازهاي گلخانه‏اي است. در اين تحقيق از داده‏هاي سطح دو ماهواره GOSAT، محصولات MOD13Q1 و MOD11C3 ماهواره MODIS و پارامترهاي هواشناسي دما، رطوبت، و بارندگي به منظور بررسي تغييرات ماهانه و فصلي گاز متان در سال 2013 استفاده شد. نتايج نشان داد گاز متان داراي افزايش ثابتي در طول اين دوره بوده است؛ به ‏طوري ‏كه ميزان آن از ppb36/1788 به ppb45/1823 افزايش يافته؛ اين موضوع نشان‏دهنده افزايش ppb 09/35 اين گاز در ايران است. گاز متان داراي نوسانات ماهانه است؛ به ‏طوري ‏كه حداكثر غلظت اين گاز در ماه‏هاي اكتبر و سپتامبر و حداقل آن در ماه‏هاي مارس و آپريل مشاهده شد. اين گاز با متغيرهاي دما و LST ارتباط مثبت دارد و با متغيرهاي NDVI، رطوبت، و بارندگي داراي ارتباط منفي است. اين امر بيان‏كننده افزايش غلظت متان در مناطقي با پوشش گياهي كم‏تراكم‏تر و با درجه حرارت بالاتر در ايران است. بنابراين، حفظ پوشش گياهي طبيعي به‏ويژه در مناطق گرم و خشك به منظور كاهش غلظت گاز متان توصيه مي‏شود.

Introduction Global warming and climate change have been identified as the most important challenges of the current century. Methane as one of the most important greenhouse, accounted for about 18% of the total increase in radiative forcing due to long-lived greenhouse gases in the atmosphere. The average CH4 concentration (XCH4) was 1808 ppb in 2010, which represents an increase of 158% from approximately 700 ppb in the pre-industrial era. Satellite observations with continuous monitoring can be used to provide the extensive information on the temporal and spatial variations of atmospheric CH4 concentration. The Greenhouse Gases Observing Satellite (GOSAT) as the first satellite in orbit dedicated to observing greenhouse gases has provided extensive research opportunities for applications using space-based greenhouse gas measurement. The main objectives of this study are investigation of methane concentration trend changes and amplitude in XCH4 from 2009 to 2015 in Iran using GOSAT data and assessment the relationship between XCH4 and Meteorological parameters obtained from weather stations and MODIS products for the year 2013 on the study area. Materials and Methods Study area The study area IS IRAN which located in Middle East Asia between between 25°-40° N and 44°- 64° E, covering approximately 1645000 km2 .The location of the study area is shown in Figure1. Data The GOSAT was launched in January 2009 which is a joint effort of the Ministry of Environment (MOE), National Institute for Environmental Studies (NIES) and Japan Aerospace Exploration Agency (JAXA). It is equipped with two sensors: The Thermal and Near-infrared Sensor for Carbon Observation Fourier Transform Spectrometer (TANSO-FTS) and the Cloud and Aerosol Imager (TANSO-CAI). MODIS (Moderate Resolution Imaging Spectroradiometer) as a key instrument aboard the Terra and Aqua is one of the most reliable data sources at the global scale. Terra MODIS and Aqua MODIS are viewing the entire Earthʹs surface every 1 to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths (see MODIS Technical Specifications).The meteorological parameters (temperature, humidity and precipitation) used in this study were obtained from the Islamic Republic of Iran Meteorological Organization (http://www.irimo.ir/).In this research, GOSAT TANSO-FTS level 2 data, MOD13Q1 and MOD11C3 products of MODIS satellite, meteorological parameters (Temperature, Precipitation and Humidity) for 2013 were used. Statistical analysis GOSAT data, MODIS products and meteorological parameters value were analyzed in SPSS statistical program. The correlation coefficient was calculated to investigation the relationships between CH4 concentration and used variable (temperature, precipitation, humidity, NDVI and LST). Analysis of Variance was applied for investigation of difference between XCH4 concentration in diffrerent years. Results and Discussion In this research, the CH4 concentrations value was calculated using TANSO-FTS sensor from 2009 to 2015 in whole of the study area. The results show a steady increase in the mean atmospheric XCH4 from 1788.36 ppb in the year 2009 to 1823.45 ppb in the year 2015 which illustrate an increase of about 35.09 ppb for a 6-year period. To assessment the monthly changes of CH4 concentration, the monthly average concentrations of this gas from 2009 to 2015 were calculated. The results reveal that CH4 concentration varied significantly between different months, with the highest concentration of XCH4 in October-September and its lowest concentration in March –April. According to the results, the coefficient of correlation between CH4 concentration and MODIS products showed that the correlation of this gas with NDVI and LST was negative and positive, respectively. As correlations coefficient for NDVI is -0.526, -0.138, -0.186 and -0.322 for spring, summer, autumn and winter, respectively. The correlation coefficient between XCH4 and LST is 0.6, 0.223, 0.458 and 0.634 for spring, summer, autumn and winter, respectively. Moreover, the coefficient of correlation between CH4 concentration and metrological parameters indicate that correlation of this gas with humidity and precipitation are negative (r humidity= -0.479, r precipitation= -0.505) and the correlation between this gas and temperature is positive (r=0.484). Its means that CH4 concentration will increases with increases in temperature and LST, and decrease in precipitation, humidity and NDVI. Conclusion The satellite monitoring of CH4 concentrations showed increase at about 35.09 ppb over time from 2009 to 2015 in the study area. We observed that the XCH4 varied significantly between different months, with the highest concentration of XCH4 in October-September and its lowest concentration in March –April. This amplitude is related to different source and sink of methane in different seasons. The correlation between this gas and NDVI, precipitation humidity was seen to be negative, and correlation between this gas and LST, temperature was positive. So it is necessary to conserve the natural ecosystems in whole of IRAN especially in arid and semi-arid regoins for decreasing CH4 concentartion.