波段位置和宽度对河口湿地4种植被NDVI的影响

Effects of Band Position and Bandwidth on NDVI Measurements of Four Kinds of Estuary Wetland Vegetation

研究不同波段位置和宽度对植被NDVI的影响,对于进一步认识NDVI指数具有重要的意义。采用ASD(Analytical Spectral Devices)地物光谱仪测定闽江河口互花米草(Spartina alterni-flora)、秋茄(Kandelia candel)、芦苇(Phragmites australis)和短叶茳芏(Cyperus malaccensis)冠层光谱,利用ViewSpecPro和Oragin8.0软件对光谱数据进行分析和处理,探讨不同波段位置和波段宽度对河口湿地4种植被NDVI的影响。结果表明:①当红光波段固定,近红外波段以50nm宽度移动时,4种湿地植被NDVI随近红外波段中心位置增加而迅速增加,之后趋于平稳,在925～1 050nm出现一个小的谷值,互花米草和短叶茳芏的谷值要比其他两种植物更为明显;不同波段宽度影响表现为:除红边与970nm附近区域对NDVI的影响较显著外,其他波段影响不显著;②当近红外波段固定,红光波段以10nm宽度移动时,4种湿地植被NDVI随红光波段中心位置移动先略有增加或变化不大,然后迅速降低;不同波段宽度影响表现为:在650～700nm波段宽度越宽,NDVI值越小,600～650nm范围内波段宽度对NDVI的影响不大;③4种湿地植被红光波段宽度对NDVI的影响要大于近红外波段。

The canopy hyperspectral reflectance data of four typical kinds of wetland vegetation （Phragmites australis,Cyperus malaccensis,Kandelia candel and Spartina alterniflora） was acquired by Analytical Spec tral Devices at the Shanyutan wetland of Minjiang river estuary in October 2011. The data was analyzed by adopting Viewspecpro and Oragin8.0 software to research the effects of band position and bandwidth on NDVI values. The following results showed that band positions and bandwidths of red band and near-infra- red （NIR） band had significant different influences on NDVI values of four kinds of wetland vegetation rel atively. （1）When the red wavelengths fixed,NDVI of all vegetation were increased rapidly along with the in crease of band center position,while NDVI appeared a small valley value in 925～1 050 nm. P. australis and S. alterniflora showed this valley value more obviously. Moreover, the different bandwidths influences on NDVI were that,in 725～825 nm,the lower NDVI values came out with the wider bandwidths; in 825～925 nm,the bandwidths had less influence on NDVI; in 925～1 100 nm,the narrower bandwidths got grea ter influences on NDVI. （2）When the NIR wavelengths fixed,the NDVI values of K. candel and S. alterniflora were increasing gradually with the increase of band center position in 600～680 nm,but P. australis and C. malaccensis did not showed this trend. In 680～ 700 nm, the NDVI of four kinds of wetland vegetation decreased rapidly. Bandwidths influences on NDVI were different with red wavelengths fixed condition. In 650～ 700 nm, the lager NDVI values came out with the narrower bandwidth; the bandwidths had less influences on NDVI in 600～650 nm. （3）The bandwidth of red band influences on NDVI values of four kinds of wetland vegetation is grea ter than the bandwidths of NIR band.