应用间接排序识别盐沼植被的光谱特征:以崇明东滩为例

doi:10.17521/cjpe.2006.0034

摘要/Abstract

摘要：

遥感技术已成为大尺度植被分类的重要手段,而地面植物群落特征与其光谱特征之间的关系是解译遥感影像的关键。该研究选择上海崇明东滩自然保护区的盐沼植物群落为对象,应用ASD地物光谱仪测定其植物群落的光谱反射率,并采用10个小型机载成像光谱仪(CASI)默认植被波段组,应用主分量分析法和相关分析分析了不同群落光谱特征与生态环境因子之间的关系。分析结果表明,间接排序法PCA能够识别盐沼植被中光滩、海三棱草(Scirpus mariqueter)群落、芦苇(Phragmites australis)群落和互花米草(Spartina alterniflora)等群落的光谱特征,绝大多数盐沼湿地植物群落组成与光谱特征之间有显著的相关,识别效果最好的波段组是736~744 nm、746~753 nm、775~784 nm、815~824 nm和860~870 nm;对光谱反射率影响最大的生态环境因子分别是植物群落的高度和盖度,高程和其它环境因子的影响次之。研究成果可为遥感监测崇明东滩自然保护区内入侵种互花米草的空间分布和扩散规律提供技术支撑,为高光谱遥感影像的影像判读和解译分类以及盐沼湿地植被制图提供科学依据。

关键词: 崇明东滩, 盐沼植被, 地物光谱仪, 小型机载成像光谱仪, 冠层反射光谱, 间接排序法

Abstract:

Remote sensing is a major source of spatial information of the attributes of the earth's surface, and remote sensing technology has become a primary tool for vegetation classification at large scales. The relationship between vegetation and their spectral characteristics is key for interpreting remote sensing images. This study related characteristics of saltmarsh vegetation at the intertidal zone of Chongming Dongtan Nature Reserve, Shanghai, to patterns of their spectral reflectance. Paired measurements of saltmarsh community and spectral characteristics were carried out along three transects covering the major variations in vegetation and environment within the study area. The spectral characteristics were measured by a ground FieldSpec Pro JR spectroradiometer and the spectral data were converted to simulate the 10 bands of Compact Airborne Spectrographic Imager (CASI) bandset. The spectral data sets were then ordinated using Principal Component Analysis (PCA), an indirect ordination technique. The eigenvalue of the first PCA axis was 19.9, which represented 98.5% of the variation in the spectral data. A sequence of bare mudflat, Scirpus mariqueter community, Spartina alterniflora community and Phragmites australis community changed along the first ordination axis showed a strong correspondence with variation in the bands six to ten, i.e. the simulated CASI wavebands covering the 736 to 870 nm wavelengths. A significant relationship between the first axis PCA scores for the spectral data of quadrats and their percentage community cover and height also was identified. The second axis accounted for only 1.4% of the variation in the spectral data and it proved impossible to demonstrate any close link between any specific plant community type and a distinct set of spectral characteristics because of its low representation of the variation in the spectral data.

Our study has demonstrated that the variation in the spectral data of saltmarsh vegetation at Chongming Dongtan Nature Reserve can be identified using the indirect ordination technique of PCA and then applying correlation and regression analyses to explain the relationships between the variation in the spectral data with the vegetation and ecological data. Our results indicate that PCA is of value for identifying relationships between community types and the spectral data of CASI bandsets for saltmarsh vegetation. This could provide an effective and practical approach for classification of saltmarsh vegetation at large scales and for monitoring spatio_temporally dynamic patterns of saltmarshes at Chongming Dongtan Nature Reserve. Further work is required in order to test these conclusions. The method has been evaluated for a single season with a limited sample of saltmarsh plant communities, and the application of PCA and spectral data of CASI bandsets to other saltmarsh vegetation as well as multi_seasonal spectral data are necessary to determine whether similar patterns emerge and whether the approach has more general applicability in terms of characterizing remote sensing/spectral imagery and community types in saltmarsh vegetation.

Key words: Chongming Dongtan, Saltmarsh vegetation, Spectroradiometer, CASI, Canopy reflectance, Indirect ordination

高占国, 张利权. 应用间接排序识别盐沼植被的光谱特征:以崇明东滩为例. 植物生态学报, 2006, 30(2): 252-260. DOI: 10.17521/cjpe.2006.0034

GAO Zhan_Guo, ZHANG Li_Quan. IDENTIFICATION OF THE SPECTRAL CHARACTERISTICS OF SALTMARSH VEGETATION USING INDIRECT ORDINATION: A CASE STUDY FROM CHONGMING DONGTAN, SHANGHAI. Chinese Journal of Plant Ecology, 2006, 30(2): 252-260. DOI: 10.17521/cjpe.2006.0034

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链接本文: https://www.plant-ecology.com/CN/10.17521/cjpe.2006.0034

https://www.plant-ecology.com/CN/Y2006/V30/I2/252

图/表 6

图1 上海崇明东滩自然保护区位置与2003年8月Landsat_TM卫星影像图

Fig.1 The location of Chongming Dongtan Nature Reserve,Shanghai,and the Landsat_TM satellite image of August, 2003

表1 小型机载成像光谱仪(CASI)默认植被波段组和波长范围

Table 1 The Compact Airborne Spectrographic Imager(CASI)default vegetation bandset and the wavelength ranges

CASI波段 CASI band	1		2	3		4	5	6		7	8		9	10
波长 Wavelengths (nm)	441~461		548~557	666~674		694~703	705~711	736~744		746~753	775~784		815~824	860~870

图2 崇明东滩湿地植物群落10个CASI波段光谱特征数据的PCA排序图a. 芦苇单优势群落 Mono_dominant community of Phragmites australis b. 互花米草单优势群落 Mono_dominant community Spartina alterniflora c. 海三棱草单优势群落 Mono_dominant community Scirpus mariqueter d. 海三棱草+糙叶苔草混合群落 Co_dominant community of Scirpus mariqueter_Carex scabrifolia ab. 芦苇与互花米草混合群落 Co_dominant community of Phragmites australis_Spartina alterniflora da. 海三棱草+糙叶苔草群落+芦苇混合群落 Mixed community of Scirpus mariqueter_Carex scabrifolia_Phragmites australis e. 光滩 Bare mudflat quadrat 字母后的数字表示样方号 The figure after the sign is the quadrat number

Fig.2 The PCA ordination plot for the spectral data sets of Compact Airborne Spectrographic Imager (CASI) bandset of the wetland vegetation at Chongming Dongtan, Shanghai

图3 10个CASI波段组的变化格局与PCA第一和第二排序轴的关系,按比例的圈点代表了每一样方中每一波段组的测定值,较大的圈点代表了较高的测定值

Fig.3 Patterns of variation in the 10 CASI wavebands in relation to the first two axes of the PCA ordination, proportional circles correspond to values for each waveband in each quadrat with higher values corresponding to larger circles

表2 10个CASI波段组光谱特征数据与PCA 排序第一和第二轴的相关性分析

Table 2 The correlation between the spectral data sets of 10 CASI wavebands and the first two axes of PCA

CASI波段 CASI band	1	2	3	4	5	6	7	8	9	10
PCA第一排序轴 PCA axis 1	0.25	-0.24	0.38^*	0.01	-0.51^*	-0.99^*	-0.99^*	-0.99^*	-0.99^*	-0.99^*
PCA第二排序轴 PCA axis 2	0.79^*	0.43^*	0.88^*	0.65^*	0.15	-0.74^*	-0.79^*	-0.78^*	-0.78^*	-0.78^*

表3 光谱特征数据的PCA排序与生态环境因子的相关性分析

Table 3 The correlation between the first two axes of PCA and the ecological and enviro nmental factors

	群落高度 Community height	群落盖度 Community cover	高程 Elevation	土壤含水量 Soil water content
PCA第一排序轴 PCA axis 1	-0.830^**	-0.685^**	-0.292^*	-0.078
PCA第二排序轴 PCA axis 2	-0.790^**	-0.842^**	-0.298^*	-0.234

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