摘要
红边位置常被用来估测植被的叶绿素/氮素含量、叶面积以及探测植被胁迫,其精确计算十分重要。目前其计算主要是基于导数光谱或曲线拟合技术,但哪种方法能更有效地探测植被的叶绿素/氮素含量,还没有一个定论。本研究以菠菜的叶片高光谱为例,详细比较了目前常用的6种红边位置提取方法与叶片叶绿素之间的关系,并从其对叶绿素含量预测的准确度、计算的难易程度、所需数据的精度及适用范围等几个方面进行了讨论。结果表明,叶片红边位置的计算结果对选择方法的依赖性很大,几种计算方法提取的红边位置与叶绿素含量的相关性均较好。四点线性内插法计算的红边位置往往偏大,最大一阶导数法与叶绿素含量的关系存在着明显的不连续性,拉格朗日内插法、倒高斯模型法在一定程度上存在着对高叶绿素含量的饱和现象,多项式拟合法对拟合波段区间、最高项次及光谱分辨率等比较灵敏而导致结果不够稳定,而线性外推法计算出的红边位置对叶绿素含量最为敏感,预测的准确度最高,且计算相对比较简单,并能适用于较宽波段的遥感数据。在实际应用时还应根据具体情况而选择合适的红边位置提取方法。
The position of the inflection point in the red edge region （680～780 nm） of the spectral reflectance signature, termed the red edge position （REP）, has been used as a means to estimate foliar chlorophyll or nitrogen content and leaf area and also as an indicator of vegetation stress. At present, extraction techniques for REP can be divided into two groups. The one is based on derivative and the other uses curve fitting. There was no conclusion about which technique can adequately track variations in spectral reflectance near the chlorophyll sensitive peaks, and precisely estimate the chlorophyll content. Maximum first derivative, Lagrangian interpolation, four-point interpolation, inverted–Gaussian modeling, polynomial fitting and linear extrapolation techniques were used to extract the REP from spinach leaf hyper reflectance spectra, and their performance for prediction of leaf chlorophyll content were also compared. Results show that the results of REP calculations are dependent upon the choice of method, and the relationship between REPs extracted by different techniques and leaf chlorophyll content were all good. REPs extracted by four-point interpolation technique are biased towards the longer wavelength and most insensitive to leaf chlorophyll content. The maximum first derivative technique is not appropriate for estimating leaf chlorophyll content because of the discontinuity it creates in the REP data and the REP/chlorophyll relationship. Lagrangian interpolation and inverted-Gaussian modeling to some extent are less sensitive to higher chlorophyll content due to the REPs saturate when leaf SPAD higher than 60. REPs extracted by polynomial fitting technique were unstable due to its high sensitivity to the spectral resolution, waveband range and the highest order of polynomial. The linear extrapolation technique was the most practical and suitable method because of its relative high correlation with a wide range of chlorophyll content, relative simple algorithm, relative high sensitivity to chlorophyll at high or low content and application to more wider bandwidth spectra. However, appropriate REP extraction technique should be chosen according to the practical situation.
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2008年第9期165-169,共5页
Transactions of the Chinese Society of Agricultural Engineering
基金
江苏省自然科学基金资助项目(BK2005167)
关键词
光谱分析
高光谱数据
叶绿素含量
估测
红边位置
蔬菜
spectrum analysis, hyper-spectral data, chlorophyll content, estimation, red edge position, vegetable
