MODIS北极气溶胶光学厚度的精度验证与分布特征研究

Accuracy validation and distribution characteristics of Arctic MODIS aerosol optical depth

北极是地球上的气候敏感区,近年来其温度升高是全球平均水平的两倍,而大气气溶胶对北极变暖有显著影响。为探究北极大气气溶胶的光学特性,基于MODIS(Moderate-resolution Imaging Spectroradiometer)10 km和3 km气溶胶光学厚度AOD(Aerosol Optical Depth)产品,分析了2000年3月—2018年10月北极地区AOD的时空分布特征,并与气溶胶自动观测网AERONET(Aerosol Robotic Network)地基站点的气溶胶观测结果进行了比较验证。结果表明,MODIS 10 km和3 km AOD与AERONET地基站点的相关系数分别为0.840和0.853,均方根误差均小于0.1,MODIS 10 km和3 km两种AOD产品与北极地面现场观测结果均具有较好的一致性。MODIS两种AOD产品与AERONET地基站点的相关系数、均方根误差、相对平均偏差和期望误差的结果均显示,北极地区MODIS 10 km AOD产品精度整体上略高于3 km AOD产品,且两者在北极东半球较其他地区的精度更高;MODIS 10 km AOD产品在西半球的误差呈现出纬度越高精度越高的特点,但3 km AOD产品没有显示这一规律;在时间上,MODIS两种AOD产品精度均在5、9和10月份较高,在秋季比春夏季略高。此外,基于北极地区MODIS AOD产品还发现,不同纬度的AOD之间存在显著差异,AOD随纬度降低不均匀增大。北极地区AOD呈现明显的季节变化,春季3—5月份AOD值普遍介于0.1~0.3,且在4月的北欧区域达到最高值;在夏季6—8月份,AOD高值范围逐渐增大;在秋季9—10月份,AOD普遍在0.1以下。两种MODIS AOD产品在北极洋面和陆面上呈现不同的特征:洋面上10 km的AOD通常更大,而陆面上3 km的AOD更大。

The Arctic is a highly climate-sensitive area.In recent years,the Arctic temperature has increased at twice the rate of the global average,and aerosols have a significant impact on Arctic warming.To explore the optical characteristics of aerosols over the Arctic,we analyze the characteristics of the spatial and temporal distributions of the Arctic aerosol optical depth(AOD)based on Moderate-resolution Imaging Spectroradiometer(MODIS)10-km and 3-km AOD products from March 2000 to October 2018 and validate these products via comparisons with the ground-based Aerosol Robotic Network(AERONET).The results indicate that the correlation coefficients between the MODIS 10-km and 3-km AODs and the AERONET base station points are 0.840 and 0.853,respectively,and that the root mean square error is less than 0.1.Both the 10-km and 3-km AODs are in good agreement with the ground-based observations.The results for the correlation coefficient,root mean square error,relative mean bias,and expected error between the two AOD products and the AERONET data all show that,overall,the accuracy of MODIS 10-km AOD products in the Arctic region is higher than 3-km AOD,and both are more accurate in the Eastern Hemisphere of the Arctic than in other regions.Moreover,the accuracy of the MODIS 10-km AOD increases as the latitude increases in the Western Hemisphere of the Arctic,although no consistent pattern is observed in the 3-km AOD.Additionally,the two AOD products typically exhibit greater accuracy in May,September,and October and are slightly more accurate in spring than in summer.Moreover,remarkable AOD differences are detected between low and high latitudes in the Arctic,where AOD increases unevenly as the latitude decreases.The Arctic MODIS AOD exhibits obvious seasonal variations.Spring AOD values generally range from 0.1 to 0.3 and peak in the Nordic region in April.In summer,high AOD values extend to larger areas from June to August,while the AOD values are typically smaller than 0.1 in autumn.Moreover,the two MODIS AOD products exhibit different patterns over Arctic land and ocean areas.The MODIS 10-km AOD is usually larger over the Arctic Ocean,while the MODIS 3-km AOD is generally larger over the Arctic land areas.