基于光谱特征的北京市冬季城市森林滞尘分布反演研究

Inversion Research on Dust Distribution of Urban Forests in Beijing in Winter Based on Spectral Characteristics

城市森林影响空气中颗粒物的过滤和吸附,可以最大限度地减少空气中颗粒物污染对人体健康的有害影响。特别是在冬季,城市森林中的常绿植物在吸收灰尘和净化空气方面起着重要作用。本研究以北京市区冬季主要的常绿植被大叶黄杨(Euonymus japonicus)为研究对象,设置3类的采样空间,采集1410个叶片,测定叶片除尘前后的高光谱数据以及叶片表面的滞尘量。通过分析不同滞尘程度影响下的叶面光谱响应特性确定敏感波段,建立滞尘前后植被指数比值与滞尘量之间的回归模型,利用Sentinel-2遥感影像反演常绿植被的滞尘分布,并对反演结果进行验证。结果表明,在510~700和758~1480 nm范围内,除尘前叶片的平均光谱反射比小于洁净叶片。封闭区域叶片除尘前后平均光谱反射率的变化小于半封闭区域,开放区域叶片除尘前后的平均光谱反射率变化最大。研究发现红波段和近红外波段对灰尘影响最敏感,与滞尘量具有较高的相关性,利用归一化差异物候指数(NDPI)建立的反演模型:x=0.93969y-0.14504(x为RNDPI的数值,y为滞尘量),决定系数R2达到0.879。反演结果表明,封闭区域的平均滞尘量小于半封闭区域和开放区域,北京城区植被高滞尘量的区域分布在南部较多,植被滞尘量从市中心到周边地区有逐渐降低的趋势。研究叶片滞尘的空间分布,为快速监测城市区域灰尘污染强度与分布提供参考,为进一步探索常绿灌木的滞尘效果,科学指导城市森林建设,改善冬季城市生活环境具有重要意义。

Urban forests affect the filtration and adsorption of airborne particulate matter,which can minimize the harmful effects on human health caused by airborne particulate pollution.Evergreen plants in urban forests play a major role in absorbing dust and purifying the air,especially in winter.In this study,Euonymus japonicus,the main evergreen vegetation in winter in Beijing,was used as the research object.Three types of sampling space were set up,and 1410 leaves were collected to measure the hyperspectral data before and after cleaning and the amount of dust absorption(ADA)on the surface of the leaf.The sensitive band was determined by analyzing the response of spectral reflectance to the amount of dust retention,and the regression model was established between the vegetation index ratio and ADA before and after cleaning.The Sentinel-2 remote sensing image was used to obtain the dust distribution of the evergreen vegetation,and the inversion results were verified.The result showed that in the range of 510~700 and 758~1480 nm,the average spectral reflectance of the blade before dust removal is less than that of the clean blade.The change of average spectral reflectance before and after cleaning in the closed zone is less than that in the semi-closed zone,and the change in the open zone is the largest.And the red band and nearinfrared band are most sensitive to dust.The inversion model established using the Normalized Difference Phenology Index(NDPI)is:x=0.93969y-0.14504(x represents the value of RNDPI,and y represents the amount of dust retention),and the determination coefficient(R2)reached 0.879.The inversion results show that the mean ADA in the enclosed area is smaller than that in semi-enclosed and open areas,and the regional distribution of high ADA in the urban area of Beijing was higher in the south with a tendency of the ADA to decrease from city centre to the surrounding area.Study the spatial distribution of leaf dust retention and provide a reference for rapid monitoring of dust pollution intensity and distribution in urban areas,and exploring the dust retention effect of evergreen shrubs are important for scientifically guiding urban forest construction and improving the living environment of cities in winter.