Gillon Dominique, Houssard Claudie, Joffre Richard
Centre d'Ecologie Fonctionnelle et Evolutive, CNRS, 1919 route de Mende, F-34293 Montpellier cedex 5, France e-mail:
Oecologia. 1999 Feb;118(2):173-182. doi: 10.1007/s004420050716.
The aim of this study was to produce calibration equations between near-infrared reflectance (NIR) spectra and the concentrations of carbon, nitrogen, and phosphorus in heterogeneous material: from living needles to litter in Pinus halepensis stands subjected to prescribed burnings. The aim was to determine whether calibrations should be conducted within each stage in the transformation of needles (local calibrations), giving relationships that were accurate but valid only for each particular stage, or whether it was possible to integrate the various forms of variation in needles (global calibrations) while retaining an acceptable accuracy. A principal component analysis calculated from the sample spectral data was used to distinguish three different sets, each sharing spectral characteristics and corresponding to three categories of needle: needles collected on the pines (N), falling needles (F), and litter (L), and each containing samples collected from the burnt sites and a control site. Samples representative of all the forms of variation in spectral properties were selected from within each category and their carbon, nitrogen, and phosphorus concentrations were measured using standard wet chemistry methods; these constituted the calibration sets n, f, and l. Calibrations were produced between the nutrient concentrations and the NIR spectra of the calibration sets n, f, and l and the grouped sets (n+f, f+l, n+f+l). The results of local calibrations made from each individual category showed that the carbon, nitrogen, and phosphorus concentrations were accurately predictable by NIR spectra. The global calibrations made by lumping together several categories were valid for a wider range of concentrations and for spectrally heterogeneous materials and in most cases were just as accurate as the local calibrations produced from each individual category.
本研究的目的是建立近红外反射率（NIR）光谱与异质材料中碳、氮和磷浓度之间的校准方程：这些异质材料包括地中海松林中从活针叶到经过规定火烧后的凋落物。目的是确定校准是应在针叶转化的每个阶段内进行（局部校准），得出仅对每个特定阶段准确且有效的关系，还是有可能整合针叶的各种变化形式（全局校准），同时保持可接受的准确性。根据样本光谱数据进行主成分分析，以区分三个不同的集合，每个集合具有共同的光谱特征，分别对应三类针叶：从松树上采集的针叶（N）、掉落的针叶（F）和凋落物（L），每个集合都包含从火烧地点和对照地点采集的样本。从每个类别中选取代表光谱特性所有变化形式的样本，并使用标准湿化学方法测量其碳、氮和磷浓度；这些样本构成校准集n、f和l。在校准集n、f和l以及分组集（n+f、f+l、n+f+l）的养分浓度与近红外光谱之间建立校准方程。由每个单独类别进行的局部校准结果表明，近红外光谱能够准确预测碳、氮和磷的浓度。将几个类别合并进行的全局校准对于更广泛的浓度范围和光谱异质材料是有效的，并且在大多数情况下与从每个单独类别得出的局部校准一样准确。
