Detection of Leaf EWT by Calculating REWT from Reflectance Spectra
叶片辐射等效水厚度计算与叶片水分定量反演研究

The spectral characteristics and the interaction between leaf and light were analyzed based on the optical absorption coefficients of foliar biochemical contents,and the method and equation to calculate the radiative-equivalent water thickness(REWT) of leaves were presented based on the reflectance difference between 945nm and 975nm bands.Because of surface direct reflectance and multi-scatter in the leaf,the REWT derived from Beer principle was quite different from the biochemical equivalent water thickness(EWT).The leaves spectra of different species at different water status were measured by our experiment and Lopex93,and the REWT values at 975nm band were calculated based on the presented method.The relation between leaves' EWT and REWT was analyzed and tested from our experimental dataset and Lopex93 dataset.The REWT was 3.3 times larger than EWT with a significant correlation coefficient(R2) of 0.80 for our dataset and 0.86 for Lopex93 dataset.The results show that:(1) the REWT can be calculated from the reflectance difference between 945nm and 975nm,and it was reliable and significantly correlated with EWT;(2) the relation between REWT and EWT reflected the leaf internal light transfer,and multi-scatter path-length in near-infrared bands was quite different from leaf thickness.