基于光能利用效率的区域蒸散量反演模型——以玉米种植区为例

以内蒙古河套地区解放闸灌域为研究区域,以实测生物量与土壤含水量及其关系方程为研究基础,建立了基于光能利用效率(radiation use efficiency,RUE)的区域蒸散量反演模型;以陆面能量平衡(surface energy balance algorithm for land,SEBAL)模型为参考,对反演的同一时期的区域蒸散量进行对比分析.结果表明:RUE与SEBAL模型反演的区域蒸散量在空间分布和纹理特征方面具有相似性且相关性较高,决定系数高于农业技术推广支持系统(decision support system for agrotechnology transfer,DSSAT)与SEBAL的;基于RUE建立的区域蒸散量反演模型能够较好地反映区域蒸散量,在监测区植被(或作物)单一的前提下,是一种有效方法.     

基于MODIS的陆地植被光合过程参数反演研究

遥感在陆地植被生产力研究中的应用,推动了遥感驱动的陆地生态系统模拟和NPP估算尺度的扩展。NPP遥感模型中,冠层吸收光合有效辐射和辐射利用率是描述植物光合过程的两个关键参数,本文根据太阳辐射在地一气系统中的传输过程和植物光合作用机理,建立基于MODIS数据的参数反演模型,重点研究地表光合有效辐射吸收总量(APARSFC)、冠层光合有效辐射吸收比(RPAR)、辐射利用率(RUE)等的定量提取,并选择东北温带落叶林为研究对象,利用2003年6月MODIS数据,探讨各自在NPP研究中的应用。研究表明：6月东北温带落叶林地表PAR净通量月均值为8．1MJm^-2day^-1;RPAR大于0．5,部分地区达到饱和;辐射利用率在0.45-1．09gC MJ^-1之间,落叶阔叶林和落叶针叶林均值分别为0．71和0．69gC MJ^-1;净光合产物月累积均值达0．53MgChm^-2,其中,落叶针叶林为0．56MgChm^-2,落叶阔叶林达0．51MgChm^-2,表现出明显的地带性规律,与过程机理模型模拟结果进行比较分析,二者差异很小,体现出良好的一致性。     

Spatial analysis of human-induced vegetation productivity decline over eastern Africa using a decade (2001–2011) of medium resolution MODIS time-series data

Climate variation and land transformations related to exploitative land uses are among the main drivers of vegetation productivity decline and ongoing land degradation in East Africa. We combined analysis of vegetation trends and cumulative rain use efficiency differences (CRD), calculated from 250-m MODIS NDVI time-series data, to map vegetation productivity loss over eastern Africa between 2001 and 2011. The CRD index values were furthermore used to discern areas of particular severe vegetation productivity loss over the observation period. Monthly 25-km Tropical Rainfall Measuring Mission (TRMM) data metrics were used to mask areas of rainfall declines not related to human-induced land productivity loss. To provide insights on the productivity decline, we linked the MODIS-based vegetation productivity map to land transformation processes using very high resolution (VHR) imagery in Google Earth (GE) and a Landsat-based land-cover change map. In total, 3.8 million ha experienced significant vegetation loss over the monitoring period. An overall agreement of 68% was found between the rainfall-corrected MODIS productivity decline map and all reference pixels discernable from GE and the Landsat map. The CRD index showed a good potential to discern areas with ‘severe’ vegetation productivity losses under high land-use intensities.