Estimating Paddy Rice Leaf Area Index with Fixed Point Continuous Observation of Near Infrared Reflectance Using a Calibrated Digital Camera
Estimating Paddy Rice Leaf Area Index with Fixed Point Continuous Observation of Near Infrared Reflectance Using a Calibrated Digital Camera
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DOI：
10.1626/pps.14.30
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发表时间：
2011-01
影响因子：
2.5
通讯作者：
M. Shibayama;T. Sakamoto;E. Takada;Akihiro Inoue;Kazuhiro Morita;W. Takahashi;A. Kimura
中科院分区：
文献类型：
--
作者：
M. Shibayama;T. Sakamoto;E. Takada;Akihiro Inoue;Kazuhiro Morita;W. Takahashi;A. Kimura
摘要一个双波段数字成像系统-一个波段为可见光红光（RED，630-670 nm），另一个波段为近红外（NIR，820-900 nm）-位于600 m2稻田上方12 m处。该成像系统自动记录鸟瞰图图像在10分钟的时间间隔从0700至1700 JST每天在2008年水稻季节。辐射校正和中期现场验证的双波段图像利用太阳辐照传感器和先前的校准计算0900-1500 JST日平均反射系数（DARF）。在红色和近红外波段的DARF值与便携式分光辐射计的观测结果一致，并显示出平稳的季节变化，植物生长。在抽穗前，近红外DARF值与叶面积指数（LAI）的相关系数（r）为0.91。使用NIR DARF值和视角与种植行方向之间的角度余弦以及视角与子午线方向之间的角度余弦，经验推导出的LAI方程显示，在从位于视野中心的四个样本点处采集的数据集（观测次数=52）估计LAI时，R2值为0.93。验证表明，该方程也适用于其他六个观测点分布在整个视场，其数据不用于推导方程参数。用太阳光谱辐射传感器标定的近红外波段观测的DARF值可用于估算水稻抽穗前叶面积指数。
Abstract A two-band digital imaging system—one band for visible red (RED, 630–670 nm) and the other for near infrared (NIR, 820–900 nm)—was positioned 12 m above a 600-m2 rice field. The imaging system automatically logged bird’s-eye-view images at 10-min intervals from 0700 to 1700 JST daily during the 2008 paddy rice season. Radiometric corrections and midterm field validations for the pairs of two-band images utilized solar irradiance sensors and prior calibrations to calculate 0900-1500 JST daily-averaged reflectance factor (DARF). The DARF values in the RED and the NIR bands agreed with observations made with a portable spectroradiometer and showed smooth seasonal changes in terms of plant growth. During the before-heading period, NIR DARF values had a correlation coefficient (r) of 0.91 with the leaf area index (LAI). An empirically derived equation for LAI using NIR DARF values and the cosines of angles between the view and the planting row directions, and the view and the meridian directions, showed R2 values of 0.93, in estimations of LAI from the dataset (number of observations=52) acquired at four sample points centrally located within the viewing field. Validation indicated that the equation also worked well for the other six observation points spread across the viewing field, the data of which were not used in deriving the equation parameters. The DARF values observed in the NIR band calibrated with solar spectral irradiance sensors were useful for assessing rice LAI during the before-heading periods.