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10.11834/jrs.20080482

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波段位置和宽度对不同生育期水稻NDVI影响研究
1.浙江大学农业遥感与信息技术应用研究所,浙江 杭州 310029;2.浙江省气象研究所,浙江 杭州 310029;3.贵州大学物理系,贵州 贵阳550025
摘要:

通过对不同生育期水稻冠层光谱的分析,探讨了不同波段位置和波段宽度对不同生育期水稻NDVI的影响.以及在一定NDVI精度要求下红光波段最大宽度和波段中心位置的相互作用.结果表明,在所有生育期,近红外波段的位置和宽度对NDVI影响不大;红光波段的位置和宽度对NDVI有较大影响,特别是红光波段位置接近红谷极值(670nm附近)时影响尤为显著.相对而言水稻生育前期的NDVI更容易受到波段位置的影响,但是波段位置对不同生育期之间NDVI的差值影响不大.无论红光波段还是近红外波段,当取值处于红边区域(690-740nm)时,对NDVI有较大影响.当保证NDVI偏差在1%以内时,在水稻生长旺期,构成NDVI的红光波段最大宽度随着波段巾心位置向长波移动而逐渐变窄,当到达690nm附近达到最窄,而后略有变宽;对于生长前期和后期,由于在648nm附近变窄而有波动.

Effects of Band Position and Bandwidth on NDVI Measurements of Rice at Different Growth Stages
Abstract:

The normalized difference vegetation index (NDVI) is themostwidely used vegetation index, which is not only applied intomany operational applications, but also is an mi portantparameter for somemodels. The objective of the study is to evaluate the effectof the red band and near-infrared (NIR) bands onNDVI, which is the function of red and NIR spectral bands, and to explore the relationship between band position and bandwidth of NDVI with the ami of monitoring the biophysical and biochemical parameters of rice.Canopy hyperspectral reflectance data of rice at seven stages were collected by portable spectroradiometer with a spectral range from 350 nm to 2500 nm. Extreme values of rice reflectance spectra in the visional and NIR regions at different stageswere identified in order to determine the suitable band center positions for red and NIR bands ofNDVI.Through the analysis ofhyperspectral reflectance, the spectralbands at674 nm and 860 nm were selected as red andNIR bands center positions, and for the computation NDVI. Then, the NDVI values were calculated under variable band position and bandwidth from hypersectraldata of rice atdifferentstages. Three scenarioswere adopted to study the effects ofband position and bandwidth on NDVI as follows. The NDVI valueswere calculated (1) from a constant red band, centered at674nm with a 10-nm bandwidth, and variable NIR band positions and bandwidths for rice, (2) from a constantNIR band, centered at 860 nm with 10-nm bandwidth,and variable red band positions and bandwidths,(3) from a constantNIR band, centered at 860 nm with a 10-nm bandwidth,and variable red band bandwidths with 674nm, 645nm as band center position, respectively. Moreover, the interactions between bandwidth and the central position of red band under the a precision requirement of 99% were analyzed too.The result indicated thatband position and bandwidth ofNIR channel have no significant influence on theNDVI of rice canopy at different development stageswhile those of red channel affect NDVI significantly, especially when band position approaches the redminmi um (near670nm).ThatmeansNDVI ismore sensitive to band position and bandwidth of red band than those ofNIR band.The sensitivity variedwith rice development stages. Relative to themiddle and later development stages of rice, the NDVI values derived from reflectance data at early development stages are more easily affected by band position. AlthoughNDVI of ricewas sensitive to band position, the difference betweenNDVI valueswas less affected by band position, therefore, the data sources should be consistentwhen NDVIwas used to study rice. In addition, theNDVI of rice atdifferentdevelopmentswas essentially affected by proxmi ity of the red andNIR bands to red edge region (690—740 nm). Under the 1% error ofNDVI, the bandwidth of red band becomes narrower when the centralposition of the bandmoves towards longerwavelengths atbloom stages, and it reaches itsminmi um at round 690nm.Beyond thatposition, the bandwidth becomes a little wider. However, for early and later development stages, the variation of red bandwidthwith central positionwasmore complicated due to the fluctuation of red bandwidth around 648 nm. The research on the effectsofband position and bandwidth onNDVIwillprovide useful information for remote sensing of rice.

Key Words:

NDVI  band position  bandwidth  rice
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