积雪与气溶胶粒子混合的光谱反照率模拟研究

积雪中的黑碳气溶胶粒子会导致积雪光谱反射率显著下降,进而引起的气候辐射变化会推迟或提前积雪融化时间,严重影响了干旱区地表径流特征、区域水循环过程,由此引起的干旱区生态水文问题也越来越受到关注。2018年1月在新疆北疆地区开展积雪中气溶胶粒子观测实验,借助ASD地物光谱仪、Snow Folk积雪特性仪与HR-1024外场分光辐射度计等仪器获取原始积雪光谱数据与其他积雪参数,应用Snow,Ice,and Aerosol Radiation model(SNICAR)模型模拟了不同雪粒径下、不同太阳天顶角、不同Black Carbon(BC)浓度下的积雪光谱反照率变化状况,讨论了BC、雪粒径在不同光谱范围内敏感性,结果表明:太阳天顶角对雪面光谱反照率的影响在近红外波段比其他波段表现得更明显,在积雪光谱曲线中太阳天顶角从0°变化到80°,可见光波段600 nm处光谱反照率升高了0.045,近红外波段1000,1200和1300 nm处光谱反照率分别升高了0.16,0.225和0.249;在天顶角为60°时,雪粒径从100μm增大到800μm,对应的光谱反照率减少量最大可达到0.15,且100~300μm范围内的雪粒径比400~800μm范围内的引起光谱反照率的下降量明显增大,雪粒径的增大能使吸光性颗粒物的光吸收效应增强;随着BC浓度的增加,积雪反照率会显著下降,且不同浓度的BC对积雪的反照率的差值不同,随着BC浓度的增加,反照率的差值量越来越小。不同的BC浓度在近红外波段对光谱反照率影响较小,影响较大的范围主要集中可见光波段,在光谱800和1100 nm处,5μg·g-1的BC浓度使光谱反照率减小了0.13和0.04,5μg·g-1的BC可使350与550 nm处的光谱反照率减小0.25与0.23;比较不同粒径下,BC浓度对积雪光谱宽波段反照率的减少情况可发现,在BC存在的情况下,雪粒径的增加会增大BC的光吸收效应,且浓度越高,吸收增加的越多;从光谱指数角度表明BC在可见光波段350~740 nm比较敏感,相关系数较高;雪粒径在近红外波段1100~1500 nm比较敏感,尤其在1000与1300 nm左右,BC与雪粒径在积雪光谱曲线中的敏感波段相关性都较高,R 2高达0.9以上;最后将模型模拟的积雪反照率与实测数据进行验证对比,R 2为0.738,模拟效果较好,可为干旱区积雪光谱反照率的研究奠定数据基础。

Simulation of Spectral Albedo Mixing of Snow and Aerosol Particles

Aerosol particles of Black carbon in the snow cause a significant decrease in the albedo spectrum of the snow,which results in climatic radiation changes seriously,and will delay or advance the snow melting time,badly affecting the characteristics of surface runoff and processes of water cycle in the arid region.This problem is receiving increasing attention in ecological hydrology issues in the arid region.The data of field measurement were obtained by ASD spectrometer,Snow Folk and HR-1024 external field spectrum radiometer.SNICAR model was used to simulate the snow spectrum spectral characteristics under different parameters.Discussed the sensitivity of BC and snow particle size in different spectral ranges.The results showed that:In the snow spectral curve,the zenith angle changes from 0°to 80°,the albedo at 600 nm in the visible spectrum increases by 0.045,and the albedo at 1000,1200 and 1300 nm in the near-infrared band increases by 0.16,0.225 and 0.249,respectively.The zenith angle is at 60°,when snow particle size increases from 100 to 800μm,the albedo reduction can reach 0.15,and snow particle size in the range of 100~300μm is significantly higher than the albedo in the range of 400~800μm.And the increase of the snow particle size can enhance the absorption effect of the light spectrum absorbing particles;Different BC concentrations have little effect on the spectral albedo in the near-infrared region,but are mainly concentrated in the visible light band.At 800 and 1100 nm,the BC concentration of 5μg·g-1 reduces the spectral albedo by 0.13.The BC of 5μg·g-1 can reduce the spectral albedo at 350 and 550 nm by 0.25 and 0.23.Compared with the different snow sizes,the decrease of BC concentration on the broad-band albedo of snow spectrum can be found in BC.In the case of the increase in the particle size of the snow,the light absorption effect of BC is increased,and at the higher concentration,the more the absorption increases;from the spectral index,the BC is sensitive in the visible light range of 350~740 nm,and the correlation coefficient is higher;The snow size is sensitive in the near-infrared band 1100~1500 nm,especially around 1000 and 1300 nm.The correlation between BC and snow particle size in the sensitive band of the snow spectral curve is high.Finally,the snow albedo simulated by the model is compared with the measured data.The R 2 is 0.738,and the simulation effect is good.It can lay a data foundation for the study of the snow albedo in the arid region.