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Changes of Canopy Reflectance Spectrum and Spectral Characteristics to Viewing Angles of Spectroradiometer: A Case Study in Rice
Changes in reflectance spectra of rice canopies taken from different viewing angles at 53 days (maximum tillering stage) and 92 days (dough stage) after transplanting of rice growth in the first cropping season of 2002. The spectral curves plotted in (a) and (c) are measured from angles face to the sun, and in (b) and (d) are measured from angles back to the sun
Changes in reflectance spectra of rice canopies taken from different viewing angles at 53 days (maximum tillering stage) and 92 days (dough stage) after transplanting of rice growth in the first cropping season of 2002. The spectral curves plotted in (a) and (c) are measured from angles face to the sun, and in (b) and (d) are measured from angles back to the sun

Author:Yuh-Jyuan Lee and Chwen-Ming Yang*

Abstract:

    Field experiments were conducted in the experimental farm of Taiwan Agricultural Research Institute at Wufeng, Taiwan to study changes of canopy reflectance spectrum and spectral characteristics to viewing angles of spectroradiometer for rice plants grown in the first and the second cropping seasons of 2002. By analysis of the ground-based remotely sensed hyperspectral reflectance data, it was found that curves of reflectance spectrum were affected by the viewing angles in both maximum tillering and dough stages in both crops. In general, reflectance was lower at nadir viewing and was increased with the increasing viewing angles. When further divided the measured spectral domain (350-2500 nm) into 10 broad bands, i.e., UV(350-400 nm), V(400-425 nm), B(425-490 nm), G(490-560 nm), Y(560-585 nm), O(585-640 nm), R(640-740nm), NIR(740-1300 nm), SWIR(1300-1800 nm), and MIR(1800-2400 nm), it was shown a quadratic function for the relationships between waveband mean reflectance and viewing angles. Again, generally reflectance was elevated with the increase of viewing angle, either face to or back to the sun. By calculating the simulated wavebands (G, R, NIR and SWIR) mean reflectance of SPOT satellite and comparing to the corresponded broad-band and narrow-band values, it indicated that usually reflectances of narrow bands were greater than values of SPOT and broad bands and were all exhibited a curvilinear trend to the viewing angles.

Key words:Oryza sativa L., Solar zenith angle, Viewing zenith angle, Narrow band, Broad band

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Journal of
Taiwan Agricultural Research
Vol. 72, No.3 (2023) ISSN: 2790-086X Vol. 72, No.3 (2023)
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