Journal of Taiwan Agricultural Research

Changes of LAImeasured, LAInb and LAI formosat-ii through the growth stages of rice (Oryza sativa L. cv. TNG 67) grown in the first cropping seasons of 2000 and the second cropping seasons of 2000 and 2001. Arrows indicate the dates of 50% of heading at the respective growing weasons

Author:Chwen-Ming Yang* and Rong-Kuen Chen

Abstract:

    This study assessed the potential for using FORMOSAT-Ⅱ data, simulated by ground-based remotely sensed high resolution reflectance spectra, to estimate growth and predict yield of rice (Oryza sativa L. cv. TNG 67) crops. Field experiments were conducted in the Taiwan Agricultural Research Institute Experimental Farm at Wufeng to measure canopy reflectance spectra, leaf area indices (LAI_measured), and yields of rice grown in the cropping seasons from 2000 to 2002. Reflectance values of broadband sensors equipped in the satellite FORMOSAT-Ⅱ were simulated by using the mean values of reflectance in the respective band regions obtained from hyperspectral data. The values of normalized difference vegetation index (NDVI) were calculated using the mean reflectance in red (630-690 nm) and near-infrared (760-900 nm) regions defined in FORMOSAT-Ⅱ. Both NDVI_NB, which was computed from narrow bands of hyperspectral data, and NDVI_FORMOSAT-Ⅱ, which was computed from simulated FORMOSAT-Ⅱ data, showed a quadratic time trend during rice growth. Changes in NDVI_FORMOSAT-Ⅱ nearly paralleled the changes in NDVI_NB, but to a lesser extent. The relationship between LAI_measured and NDVI_NB was fitted well by an exponential function, through which the estimates of satellite LAI (LAI_FORMOSAT-Ⅱ) were obtained. Results further showed that values of LAI_FORMOSAT-Ⅱ were lower than values of LAI_NB along plant development, while both of these estimated LAI_s were lower than LAI_measured after approximately 55 days after transplanting. Results indicated that yield may be predicted by the accumulated values of LAI_measured during the growing periods. By substituting LAI_measured with the values of LAI_NB and LAI_FORMOSAT-Ⅱ, it was found that the predicted yields were lower than the measured yields. Results suggest that the lower predicted yield by the FORMOSAT-Ⅱ satellite data is attributable to lower level of LAI_FORMOSAT-Ⅱ as aforementioned.

Key words:FORMOSAT Ⅱ, Hyperspectral reflectance, Rice growth estimation, Yield prediction, Simulation

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