Atmospheric Correction for Tower-Based Solar-Induced Chlorophyll Fluorescence Observations at O2-A Band
Atmospheric Correction for Tower-Based Solar-Induced Chlorophyll Fluorescence Observations at O2-A Band
复制标题
O-2-A 波段基于塔的太阳诱导叶绿素荧光观测的大气校正
DOI：
10.3390/rs11030355
复制
发表时间：
2019
期刊：
影响因子：
5
通讯作者：
Liangyun Liu
中科院分区：
文献类型：
--
作者：
Xinjie Liu;Jian Guo;Jiaochan Hu;Liangyun Liu
太阳诱导的叶绿素荧光(SIF)已被证明是植被光合作用的有效指标。为了研究SIF和总初级生产力(GPP)之间的关系，需要基于塔基的连续光谱观测和涡动协方差(EC)测量。由于O2-A吸收波段的强吸收效应对基于夫琅和费线分辨(FLD)原理的SIF反演有明显的影响，因此即使是在冠层上方几十米处使用传感器进行塔基SIF观测，也需要进行大气改正。在这项研究中，提出了一种可操作的简单的O2-A波段塔基SIF观测的大气改正方案。气溶胶光学厚度(AOD)和辐射传输路径长度(RTPL)是影响氧吸收带上、下透过率的主要因素。在中分辨率大气传输模式(MODTRAN 5)模拟的基础上，建立了利用AOD和RTPL估算大气透过率的查找表(LUT)，并利用790 nm向下辐射与660 nm向下辐射的比值(E790/E660)估算了大气光学厚度。利用基于经验公式的RTPL校正因子，对温度和气压对大气透过率的影响进行了补偿。为了评估塔基SIF观测的大气校正方法的性能，进行了一系列的现场测量。经大气改正后，塔基观测与地面观测的应力强度因子之差明显减小。结果表明，基于LUT的大气校正方法是有效的，对于更精确的塔基SIF反演也是必要的，特别是在O2-A波段。
Solar-induced chlorophyll fluorescence (SIF) has been proven to be an efficient indicator of vegetation photosynthesis. To investigate the relationship between SIF and Gross Primary Productivity (GPP), tower-based continuous spectral observations coordinated with eddy covariance (EC) measurements are needed. As the strong absorption effect at the O2-A absorption bands has an obvious influence on SIF retrieval based on the Fraunhofer Line Discrimination (FLD) principle, atmospheric correction is required even for tower-based SIF observations made with a sensor tens of meters above the canopy. In this study, an operational and simple solution for atmospheric correction of tower-based SIF observations at the O2-A band is proposed. The aerosol optical depth (AOD) and radiative transfer path length (RTPL) are found to be the dominant factors influencing the upward and downward transmittances at the oxygen absorption band. Look-up tables (LUTs) are established to estimate the atmosphere transmittance using AOD and RTPL based on the MODerate resolution atmospheric TRANsmission 5 (MODTRAN 5) model simulations, and the AOD is estimated using the ratio of the downwelling irradiance at 790 nm to that at 660 nm (E790/E660). The influences of the temperature and pressure on the atmospheric transmittance are also compensated for using a corrector factor of RTPL based on an empirical equation. A series of field measurements were carried out to evaluate the performance of the atmospheric correction method for tower-based SIF observations. The difference between the SIF retrieved from tower-based and from ground-based observations decreased obviously after the atmospheric correction. The results indicate that the atmospheric correction method based on a LUT is efficient and also necessary for more accurate tower-based SIF retrieval, especially at the O2-A band.