عنوان مقاله [English]
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 gasses 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. This 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 dedicated to the observation of 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 of 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
The study area of this research is IRAN located in Middle East Asia between 25°-40° N and 44°- 64° E, covering approximately 1645000 km2. The location of the study area is shown in Figure1.
The GOSAT was launched in January 2009 as 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 Earth's 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, we used GOSAT TANSO-FTS level 2 data, MOD13Q1 and MOD11C3 products of MODIS satellite, meteorological parameters (Temperature, Precipitation and Humidity) for 2013.
GOSAT data, MODIS products and meteorological parameter value were analyzed in SPSS statistical program. The correlation coefficient was calculated to investigate 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 concentrations in different years.
Results and Discussion
In this research, the CH4 concentration values were calculated using TANSO-FTS sensor from 2009 to 2015 in whole 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. This illustrates an increase of about 35.09 ppb for a 6-year period. To assess the monthly changes of CH4 concentration, we calculated the monthly average concentrations of this gas from 2009 to 2015. The results reveal that CH4 concentration was changed 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). This means that CH4 concentration will increases with increases in temperature and LST, and decrease in precipitation, humidity and NDVI.
The satellite monitoring of CH4 concentrations showed increase in about 35.09 ppb over time from 2009 to 2015 in the study area. We observed that the XCH4 was changed 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 sources and sink of methane in different seasons. The correlation between this gas and NDVI and precipitation humidity was negative, and correlation between this gas and LST, and temperature was positive. Therefore, it is necessary to conserve the natural ecosystems in whole IRAN especially in arid and semi-arid regions for decreasing CH4 concentrations.