de Sousa Celio Helder Resende, Hilker Thomas, Waring Richard, de Moura Yhasmin Mendes, Lyapustin Alexei
Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA.
Department of Forest Engineering, Resources and Management, Oregon State University, Corvallis, OR 97331, USA.
Remote Sens (Basel). 2017;9(1):48. doi: 10.3390/rs9010048. Epub 2017 Jan 7.
Although quantifying the massive exchange of carbon that takes place over the Amazon Basin remains a challenge, progress is being made as the remote sensing community moves from using traditional, reflectance-based vegetation indices, such as the Normalized Difference Vegetation Index (NDVI), to the more functional Photochemical Reflectance Index (PRI). This new index, together with satellite-derived estimates of canopy light interception and Sun-Induced Fluorescence (SIF), provide improved estimates of Gross Primary Production (GPP). This paper traces the development of these new approaches, compares the results of their analyses from multiple years of data acquired across the Amazon Basin and suggests further improvements in instrument design, data acquisition and processing. We demonstrated that our estimates of PRI are in generally good agreement with eddy-flux tower measurements of photosynthetic light use efficiency (ε) at four sites in the Amazon Basin: r values ranged from 0.37 to 0.51 for northern flux sites and to 0.78 for southern flux sites. This is a significant advance over previous approaches seeking to establish a link between global-scale photosynthetic activity and remotely-sensed data. When combined with measurements of Sun-Induced Fluorescence (SIF), PRI provides realistic estimates of seasonal variation in photosynthesis over the Amazon that relate well to the wet and dry seasons. We anticipate that our findings will steer the development of improved approaches to estimate photosynthetic activity over the tropics.
尽管量化亚马逊河流域发生的大规模碳交换仍是一项挑战，但随着遥感界从使用传统的基于反射率的植被指数（如归一化植被指数（NDVI））转向更具功能性的光化学反射指数（PRI），相关工作正在取得进展。这个新指数，连同卫星对冠层光截获和太阳诱导荧光（SIF）的估计，为总初级生产力（GPP）提供了更精确的估计。本文追溯了这些新方法的发展历程，比较了从亚马逊河流域多年采集数据的分析结果，并提出了仪器设计、数据采集和处理方面的进一步改进建议。我们证明，我们对PRI的估计与亚马逊河流域四个站点光合光利用效率（ε）的涡度通量塔测量结果总体上高度一致：北部通量站点的r值范围为0.37至0.51，南部通量站点的r值为0.78。这相对于此前试图在全球尺度光合活动与遥感数据之间建立联系的方法有了显著进步。当与太阳诱导荧光（SIF）测量结果相结合时，PRI能够对亚马逊地区光合作用的季节变化做出符合实际的估计，且与干湿季节密切相关。我们预计，我们的研究结果将引领估算热带地区光合活动的改进方法的发展。
