Estimating the Total Nitrogen Concentration of Reed Canopy with Hyperspectral Measurements Considering a Non-Uniform Vertical Nitrogen Distribution
Estimating the Total Nitrogen Concentration of Reed Canopy with Hyperspectral Measurements Considering a Non-Uniform Vertical Nitrogen Distribution
复制标题
考虑非均匀垂直氮分布的高光谱测量芦苇冠层总氮浓度
DOI：
10.3390/rs8100789
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发表时间：
2016-10-01
期刊：
影响因子：
5
通讯作者：
Li, Xinchuan
中科院分区：
文献类型：
--
作者：
Luo, Juhua;Ma, Ronghua;Li, Xinchuan
湿地植物的总氮浓度（NC，g/100 g）是评价湿地健康状况和计算湿地植物氮储量的重要参数。遥感已被广泛用于估算植物的生物物理、生理和生化参数。然而，目前的研究不重视NC估计，仅考虑氮的垂直分布，导致有限的准确性和实用价值的结果下降。本研究的主要目标是开发一个模型，考虑到不均匀的垂直氮分布，估计总NC的芦苇冠层，这是湿地的优势物种之一，使用高光谱数据。60个样方的选择和测量的基础上的实验设计，考虑垂直层次划分芦苇冠层。利用样方不同叶层氮素含量的实测数据和相应的光谱数据，结果表明，氮素含量的垂直分布规律明显，从表层到底层呈现先增加后减少的趋势。光谱指数MCARI/MTVI 2、TCARI/OSAVI、MMTCI、DCNI和PPR/NDVI与氮素相关时R2值较高（R2 > 0.5），与叶面积指数相关时R2值较低（R2 < 0.2），能减小叶面积指数的影响，提高芦苇冠层对氮素变化的敏感性。这些光谱指数的相对变化率（Rv，%），从每个样方计算，也表明，顶部的三层芦苇冠层是一个有效的深度，估计NC使用高光谱数据。建立了基于PPR/DNVI的芦苇冠层总氮估算模型，R2 = 0.88，RMSE = 0.37%。该模型综合考虑了氮素垂直分布格局和有效冠层，对估算整个芦苇冠层氮素总量具有很大潜力。
The total nitrogen concentration (NC, g/100 g) of wetland plants is an important parameter to estimate the wetland health status and to calculate the nitrogen storage of wetland plants. Remote sensing has been widely used to estimate biophysical, physiological, and biochemical parameters of plants. However, current studies place little emphasis on NC estimations by only taking nitrogen’s vertical distribution into consideration, resulting in limited accuracy and decreased practical value of the results. The main goal of this study is to develop a model, considering a non-uniform vertical nitrogen distribution to estimate the total NC of the reed canopy, which is one of the wetland’s dominant species, using hyperspectral data. Sixty quadrats were selected and measured based on an experimental design that considered vertical layer divisions within the reed canopy. Using the measured NCs of different leaf layers and corresponding spectra from the quadrats, the results indicated that the vertical distribution law of the NC was distinct, presenting an initial increase and subsequent decrease from the top layer to the bottom layer. The spectral indices MCARI/MTVI2, TCARI/OSAVI, MMTCI, DCNI, and PPR/NDVI had high R2 values when related to NC (R2 > 0.5) and low R2 when related to LAI (R2 < 0.2) and could minimize the influence of LAI and increase the sensitivity to changes in NC of the reed canopy. The relative variation rates (Rv, %) of these spectral indices, calculated from each quadrat, also indicated that the top three layers of the reed canopy were an effective depth to estimate NCs using hyperspectral data. A model was developed to estimate the total NC of the whole reed canopy based on PPR/DNVI with R2 = 0.88 and RMSE = 0.37%. The model, which considered the vertical distribution patterns of the NC and the effective canopy layers, has demonstrated great potential to estimate the total NC of the whole reed canopy.