Clouds can influence climate through many complex interactions within the hydrological cycle. Due to the important effects of cloud cover on climate, it is essential to study its variability over certain geographical ...Clouds can influence climate through many complex interactions within the hydrological cycle. Due to the important effects of cloud cover on climate, it is essential to study its variability over certain geographical areas. This study provides a spatial and temporal distribution of sky conditions, cloudy, partly cloudy, and clear days, in Iran. Cloud fraction parameters were calculated based on the cloud product （collection 6_L2） obtained from the Moderate Resolution Imaging Spectroradiorneter （MODIS） sensors on board the Terra （MOD06） and Aqua （MYD06） satellites. The cloud products were collected daily from January 1, 2003 to December 31, 2014 （12 years） with a spatial resolution of 5 km × 5 km. First, the cloud fraction data were converted into a regular geographic coordinate network over Iran. Then, the estimations from both sensors were analyzed. Results revealed that the maximum annual frequency of cloudy days occurs along the southern shores of the Caspian Sea, while the minimum annual frequency occurs in southeast Iran. On average, the annual number of cloudy and clear-sky days was 88 and 256 d from MODIS Terra, as compared to 96 and 244 d from MODIS Aqua. Generally, cloudy and partly cloudy days decrease from north to south, and MODIS Aqua overestimates the cloudy and partly cloudy days compared to MODIS Terra.展开更多
This study compares the aerosol optical depth (AOD) Level 2 Collection 5 products from the Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS) with ground-based measurements from a Microtops II sun p...This study compares the aerosol optical depth (AOD) Level 2 Collection 5 products from the Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS) with ground-based measurements from a Microtops II sun photometer over Sanya (18.23°N,109.52°E),a tropical coastal site in China,from July 2005 to June 2006.The results indicate that the Terra and Aqua MODIS AOD retrievals at 550 nm have good correlations with the measurements from the Microtops II sun photometer.The correlation coefficients for the linear regression fits (R2) are 0.83 for Terra and 0.78 for Aqua,and the regressed intercepts are near zero (0.005 for Terra,0.009 for Aqua).However,the Terra and Aqua MODIS are found to consistently underestimate AOD with respect to the Microtops II sun photometer,with slope values of 0.805 (Terra) and 0.767 (Aqua).The comparison of the monthly mean AOD indicates that for each month,the Terra and Aqua MODIS retrievals are matched with corresponding Microtops measurements but are systematically less than those of the Microtops.This validation study indicates that the Terra and Aqua MODIS AOD retrievals can adequately characterize the AOD distributions over the tropical coastal region of China,but further efforts to eliminate systematic errors are needed.展开更多
The Moderate Resolution Imaging Spectroradiometer （MODIS） is one of the key instruments for NASA＇s Earth Observing System （EOS）, currently operating on both the Terra and Aqua satellites. The MODIS is a major adv...The Moderate Resolution Imaging Spectroradiometer （MODIS） is one of the key instruments for NASA＇s Earth Observing System （EOS）, currently operating on both the Terra and Aqua satellites. The MODIS is a major advance over the previous generation of sensors in terms of its spectral, spatial, and temporal resolutions. It has 36 spectral bands： 20 reflective solar bands （RSB） with center wavelengths from 0.41 to 2.1 μm and 16 thermal emissive bands （TEB） with center wavelengths from 3.7 to 14.4 μm, making observations at three spatial resolutions： 250 m （bands 1-2）, 500 m （bands 3-7）, and lkm （bands 8-36）. MODIS is a cross-track scanning radiometer with a wide field-of-view, providing a complete global coverage of the Earth in less than 2 days. Both Terra and Aqua MODIS went through extensive pre-launch calibration and characterization at various levels. In orbit, the calibration and characterization tasks are performed using its on-board calibrators （OBCs） that include a solar diffuser （SD） and a solar diffuser stability monitor （SDSM）, a v-grooved flat panel blackbody （BB）, and a spectro-radiometric calibration assembly （SRCA）. In this paper, we present an overview of MODIS calibration and characterization activities, methodologies, and lessons learned from pre-launch characterization and in-orbit operation. Key issues discussed in this paper include in-orbit efforts of monitoring the noise characteristics of the detectors, tracking the solar diffuser and optics degradations, and updating the sensor＇s response versus scan angle. The experiences and lessons learned through MODIS have played and will continue to play major roles in the design and characterization of future sensors.展开更多
利用卫星数据遥感陆地气溶胶一直是国际上研究的难点与热点.利用新一代传感器MODIS(中分辨率成像光谱仪)数据,DDV(Dark Dense Vegetation)算法反演陆地气溶胶的分布以及性质已经取得了较好的效果.然而,该算法只适用于诸如水体、浓密植...利用卫星数据遥感陆地气溶胶一直是国际上研究的难点与热点.利用新一代传感器MODIS(中分辨率成像光谱仪)数据,DDV(Dark Dense Vegetation)算法反演陆地气溶胶的分布以及性质已经取得了较好的效果.然而,该算法只适用于诸如水体、浓密植被等较低地表反射率区域,大大限制了该算法的实际应用范围,尤其是无法应用于城市等亮地表区域气溶胶的遥感反演.文中提出了基于利用TERRA和AQUA双星MODIS数据的协同反演模型算法(SYNTAM-Synergy of Terra and Aqua MODIS),用以反演陆地气溶胶的光学厚度等信息.该算法实现了地表反射率与气溶胶光学厚度的同时反演,可应用于各种地表反射率类型,包括城市等亮地表区域.通过与国际AERONET的地面观测数据对比做初步的反演验证,结果表明,该算法具有较高的精度,进一步的验证工作还在继续.展开更多
Across the Arctic changes in active layer, melting of glaciers and ground ice, thawing of permafrost and sequestration changes of carbon storage are driven in part by variations of land surface heat absorption, conduc...Across the Arctic changes in active layer, melting of glaciers and ground ice, thawing of permafrost and sequestration changes of carbon storage are driven in part by variations of land surface heat absorption, conduction and re-radiation relative to solar irradiance. We investigate Arctic land-surface temperature changes and regional variations derived by the MODIS sensors on NASA Aqua and Terra from March 2000 through July 2012. Over this decadal period we detect increase in the number of days with daytime land-surface temperature above 0℃. There are indications of increasing trends of land-surface temperature change. Regional variations of the changes in land-surface temperature likely arise due to surface material types and topography relative to the daytime variation of solar irradiance.展开更多
Arctic nighttime land-surface temperatures derived by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard the NASA Terra and Aqua satellites are investigated. We use the local equator crossing ti...Arctic nighttime land-surface temperatures derived by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard the NASA Terra and Aqua satellites are investigated. We use the local equator crossing times of 22:30 and 01:30, respectively, in the analysis of changes, trends and variations on the Arctic region and within 120° sectors. We show increases in the number of days above 0°C and significant increase trends over their decadal periods of March 2000 through 2010 (MODIS Terra) and July 2002 through 2012 (MODIS Aqua). The MODIS Aqua nighttime Arctic land-surface temperature change, +0.2°C ± 0.2°C with P-value of 0.01 indicates a reduction relative to the MODIS Terra nighttime Arctic land-surface temperature change, +1.8°C ± 0.3°C with P-value of 0.01. This reduction is a decadal non-stationary component of the Arctic land-surface temperature changes. The reduction is greatest, -1.3°C ± 0.2°C with P-value of 0.01 in the Eastern Russia— Western North American sector of the Arctic during the July 2002 through 2012.展开更多
论文利用2005年Terra/MODIS卫星8天合成的250m地表反射率数据（MODIS Terra Sur-face Reflectance 8-Day L3 Global 250 m：MOD09Q1）构建的时间序列数据集，通过计算NDVI指数，结合典型地物的谱间特征，并借助SRTM数字高程数据，采用...论文利用2005年Terra/MODIS卫星8天合成的250m地表反射率数据（MODIS Terra Sur-face Reflectance 8-Day L3 Global 250 m：MOD09Q1）构建的时间序列数据集，通过计算NDVI指数，结合典型地物的谱间特征，并借助SRTM数字高程数据，采用多源信息提取的方法对洞庭湖地区2005年水域面积变化进行了动态监测。结合Terra/MODIS数据特点，提出了全年最大淹没时间指数的概念，并通过对该指数的构建，完成了对洞庭湖地区重点水域的淹没风险评价。结果表明：①文中提出的基于Terra/MODIS MOD09Q1数据的多源信息水体提取方法，通过更高空间分辨率ENVISAT/ASAR数据以及水文测站水位数据的检验表明，是切实可行的；②2005年洞庭湖地区水域面积变化特征总体表现为，在11-4月份期间水域面积较小，而在5-10月份期间较大。其中，4月份最小，9月份最大，两者相差了几乎1.5倍，受地区季节性降雨的年内分布规律及长江主汛期的影响显著；③通过全年最大淹没时间指数的计算发现，占研究区总面积84.13%的年内持久陆地和持久水域区域，基本上没有防洪压力，而剩余的15.87%的年内变化水域，由于潜在淹没风险的存在，则需要抗洪防险部门进行重点防控；④文中多源信息水面提取方法的实现以及全年最大淹没时间指数概念的提出，为今后更加深入地探讨三峡工程建成运营对洞庭湖地区水域变化以及江湖关系的影响奠定了基础。展开更多
针对Aqua和Terra MODIS AOD数据利用线性回归算法拟合结果不够精确的问题,本文提出了二次多项式回归算法对其进行拟合,二次多项式是指这个多项式的项数超过1,且最高次方数为2。采用二次多项式回归和线性回归算法分别对2015年随机选择的...针对Aqua和Terra MODIS AOD数据利用线性回归算法拟合结果不够精确的问题,本文提出了二次多项式回归算法对其进行拟合,二次多项式是指这个多项式的项数超过1,且最高次方数为2。采用二次多项式回归和线性回归算法分别对2015年随机选择的一天和4—6月的AOD数据进行拟合,并将两种方法拟合的结果进行对比分析。研究结果显示,针对同一组Aqua和Terra MODIS AOD数据的拟合,二次多项式回归方法拟合得到的RMSE、MAE、R值比线性回归拟合方法得到的值精度都要高很多,说明二次多项式回归拟合方法在Aqua和Terra MODIS AOD数据的拟合方面优于线性回归方法的拟合,证明了二次多项式回归拟合方法适用于此方面的研究,而且能够提升Aqua和Terra MODIS AOD数据拟合结果的精度。展开更多
基金Under the auspices of Faculty of Geographical Science and Planning,University of Isfahan,Doctoral Climatology Project(No.168607/94)
文摘Clouds can influence climate through many complex interactions within the hydrological cycle. Due to the important effects of cloud cover on climate, it is essential to study its variability over certain geographical areas. This study provides a spatial and temporal distribution of sky conditions, cloudy, partly cloudy, and clear days, in Iran. Cloud fraction parameters were calculated based on the cloud product （collection 6_L2） obtained from the Moderate Resolution Imaging Spectroradiorneter （MODIS） sensors on board the Terra （MOD06） and Aqua （MYD06） satellites. The cloud products were collected daily from January 1, 2003 to December 31, 2014 （12 years） with a spatial resolution of 5 km × 5 km. First, the cloud fraction data were converted into a regular geographic coordinate network over Iran. Then, the estimations from both sensors were analyzed. Results revealed that the maximum annual frequency of cloudy days occurs along the southern shores of the Caspian Sea, while the minimum annual frequency occurs in southeast Iran. On average, the annual number of cloudy and clear-sky days was 88 and 256 d from MODIS Terra, as compared to 96 and 244 d from MODIS Aqua. Generally, cloudy and partly cloudy days decrease from north to south, and MODIS Aqua overestimates the cloudy and partly cloudy days compared to MODIS Terra.
基金supported by the National Basic Research Program of China (Grant No. 2006CB 403702)
文摘This study compares the aerosol optical depth (AOD) Level 2 Collection 5 products from the Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS) with ground-based measurements from a Microtops II sun photometer over Sanya (18.23°N,109.52°E),a tropical coastal site in China,from July 2005 to June 2006.The results indicate that the Terra and Aqua MODIS AOD retrievals at 550 nm have good correlations with the measurements from the Microtops II sun photometer.The correlation coefficients for the linear regression fits (R2) are 0.83 for Terra and 0.78 for Aqua,and the regressed intercepts are near zero (0.005 for Terra,0.009 for Aqua).However,the Terra and Aqua MODIS are found to consistently underestimate AOD with respect to the Microtops II sun photometer,with slope values of 0.805 (Terra) and 0.767 (Aqua).The comparison of the monthly mean AOD indicates that for each month,the Terra and Aqua MODIS retrievals are matched with corresponding Microtops measurements but are systematically less than those of the Microtops.This validation study indicates that the Terra and Aqua MODIS AOD retrievals can adequately characterize the AOD distributions over the tropical coastal region of China,but further efforts to eliminate systematic errors are needed.
文摘The Moderate Resolution Imaging Spectroradiometer （MODIS） is one of the key instruments for NASA＇s Earth Observing System （EOS）, currently operating on both the Terra and Aqua satellites. The MODIS is a major advance over the previous generation of sensors in terms of its spectral, spatial, and temporal resolutions. It has 36 spectral bands： 20 reflective solar bands （RSB） with center wavelengths from 0.41 to 2.1 μm and 16 thermal emissive bands （TEB） with center wavelengths from 3.7 to 14.4 μm, making observations at three spatial resolutions： 250 m （bands 1-2）, 500 m （bands 3-7）, and lkm （bands 8-36）. MODIS is a cross-track scanning radiometer with a wide field-of-view, providing a complete global coverage of the Earth in less than 2 days. Both Terra and Aqua MODIS went through extensive pre-launch calibration and characterization at various levels. In orbit, the calibration and characterization tasks are performed using its on-board calibrators （OBCs） that include a solar diffuser （SD） and a solar diffuser stability monitor （SDSM）, a v-grooved flat panel blackbody （BB）, and a spectro-radiometric calibration assembly （SRCA）. In this paper, we present an overview of MODIS calibration and characterization activities, methodologies, and lessons learned from pre-launch characterization and in-orbit operation. Key issues discussed in this paper include in-orbit efforts of monitoring the noise characteristics of the detectors, tracking the solar diffuser and optics degradations, and updating the sensor＇s response versus scan angle. The experiences and lessons learned through MODIS have played and will continue to play major roles in the design and characterization of future sensors.
文摘利用卫星数据遥感陆地气溶胶一直是国际上研究的难点与热点.利用新一代传感器MODIS(中分辨率成像光谱仪)数据,DDV(Dark Dense Vegetation)算法反演陆地气溶胶的分布以及性质已经取得了较好的效果.然而,该算法只适用于诸如水体、浓密植被等较低地表反射率区域,大大限制了该算法的实际应用范围,尤其是无法应用于城市等亮地表区域气溶胶的遥感反演.文中提出了基于利用TERRA和AQUA双星MODIS数据的协同反演模型算法(SYNTAM-Synergy of Terra and Aqua MODIS),用以反演陆地气溶胶的光学厚度等信息.该算法实现了地表反射率与气溶胶光学厚度的同时反演,可应用于各种地表反射率类型,包括城市等亮地表区域.通过与国际AERONET的地面观测数据对比做初步的反演验证,结果表明,该算法具有较高的精度,进一步的验证工作还在继续.
文摘Across the Arctic changes in active layer, melting of glaciers and ground ice, thawing of permafrost and sequestration changes of carbon storage are driven in part by variations of land surface heat absorption, conduction and re-radiation relative to solar irradiance. We investigate Arctic land-surface temperature changes and regional variations derived by the MODIS sensors on NASA Aqua and Terra from March 2000 through July 2012. Over this decadal period we detect increase in the number of days with daytime land-surface temperature above 0℃. There are indications of increasing trends of land-surface temperature change. Regional variations of the changes in land-surface temperature likely arise due to surface material types and topography relative to the daytime variation of solar irradiance.
文摘Arctic nighttime land-surface temperatures derived by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard the NASA Terra and Aqua satellites are investigated. We use the local equator crossing times of 22:30 and 01:30, respectively, in the analysis of changes, trends and variations on the Arctic region and within 120° sectors. We show increases in the number of days above 0°C and significant increase trends over their decadal periods of March 2000 through 2010 (MODIS Terra) and July 2002 through 2012 (MODIS Aqua). The MODIS Aqua nighttime Arctic land-surface temperature change, +0.2°C ± 0.2°C with P-value of 0.01 indicates a reduction relative to the MODIS Terra nighttime Arctic land-surface temperature change, +1.8°C ± 0.3°C with P-value of 0.01. This reduction is a decadal non-stationary component of the Arctic land-surface temperature changes. The reduction is greatest, -1.3°C ± 0.2°C with P-value of 0.01 in the Eastern Russia— Western North American sector of the Arctic during the July 2002 through 2012.
文摘论文利用2005年Terra/MODIS卫星8天合成的250m地表反射率数据（MODIS Terra Sur-face Reflectance 8-Day L3 Global 250 m：MOD09Q1）构建的时间序列数据集，通过计算NDVI指数，结合典型地物的谱间特征，并借助SRTM数字高程数据，采用多源信息提取的方法对洞庭湖地区2005年水域面积变化进行了动态监测。结合Terra/MODIS数据特点，提出了全年最大淹没时间指数的概念，并通过对该指数的构建，完成了对洞庭湖地区重点水域的淹没风险评价。结果表明：①文中提出的基于Terra/MODIS MOD09Q1数据的多源信息水体提取方法，通过更高空间分辨率ENVISAT/ASAR数据以及水文测站水位数据的检验表明，是切实可行的；②2005年洞庭湖地区水域面积变化特征总体表现为，在11-4月份期间水域面积较小，而在5-10月份期间较大。其中，4月份最小，9月份最大，两者相差了几乎1.5倍，受地区季节性降雨的年内分布规律及长江主汛期的影响显著；③通过全年最大淹没时间指数的计算发现，占研究区总面积84.13%的年内持久陆地和持久水域区域，基本上没有防洪压力，而剩余的15.87%的年内变化水域，由于潜在淹没风险的存在，则需要抗洪防险部门进行重点防控；④文中多源信息水面提取方法的实现以及全年最大淹没时间指数概念的提出，为今后更加深入地探讨三峡工程建成运营对洞庭湖地区水域变化以及江湖关系的影响奠定了基础。
文摘针对Aqua和Terra MODIS AOD数据利用线性回归算法拟合结果不够精确的问题,本文提出了二次多项式回归算法对其进行拟合,二次多项式是指这个多项式的项数超过1,且最高次方数为2。采用二次多项式回归和线性回归算法分别对2015年随机选择的一天和4—6月的AOD数据进行拟合,并将两种方法拟合的结果进行对比分析。研究结果显示,针对同一组Aqua和Terra MODIS AOD数据的拟合,二次多项式回归方法拟合得到的RMSE、MAE、R值比线性回归拟合方法得到的值精度都要高很多,说明二次多项式回归拟合方法在Aqua和Terra MODIS AOD数据的拟合方面优于线性回归方法的拟合,证明了二次多项式回归拟合方法适用于此方面的研究,而且能够提升Aqua和Terra MODIS AOD数据拟合结果的精度。
