水稻不同期作植被反射光議之動態分析

Abstract

本項研究針對近地面侦測之田間水稻於一、二期稻作全生育期間之植被高解析光譜進行分析，期以瞭解期作問植被光譜之動態變化，並探討光譜曲線之特徵與特性，作爲未來應用於栽培管理等多元用途。根據本硏究結果，水稻植被反射光譜與多數的綠色植被光譜相似，紫外光波段(uv)及可見光波段(vis)之反射比較低，分別小於8及16%，近紅外光(nir)、短波紅外光(swir)及中紅外光(mwir)等波段之反射比較高，分別大於14、7 及4%，各波段均隨生育進展而異。又在可見光波段中，綠光之550 nm附近的反射比値較高，紫光之400-413 nm及紅光之670 nm部位則較低。而近紅外光波段反射比介於14-55%之間，短波紅外光波段介於7-31%，中紅外光波段介於4-24%之間，高低差距甚大。一、二期稻作的反射光譜曲線類似，惟各波段的反射比變化存有差異，顯示各期作之不同環 境爲影《原因之一。各生育期之光譜曲線變異亦不一致，反映出各生育階段之植被色澤、形態及結構上的差異。由綠光、紅光及近紅外光等波段之光譜特徵，發現其在全生育期間呈現曲線變化，前二項爲凹形曲線，後者爲凸形曲線。在所觀察的六項指數中，RED/NIR、RED/GREBN及GREEN/NIR等比値均爲凹形二次曲線，NDVI及RES則爲凸形二次曲線演變，唯REIP隨著生育進展而上升，故紅光臨界轉折點(REIP)之位移可供釐 訂區分水稻不同生育階段之參考。 Canopy reflectance spectra of hyperspeetral resolution from rice plants grown in the first and the second cropping seasons of 2000 were analyzed to study the dynamic variations of spectral curves and the spectral characteristics. As the results indicated that canopy reflectance spectrum was similar to those from other green plants. The reflectance was lower in the ultraviolet (< 8%) and visible (< 16%) wavebands and higher in the near infrared (> 14%), short-wave infrared (> 7%), and middle-wave infrared (> 4%) regions, and varied during the growth. In the visible light, the maximum reflectance was located near 550 nm of green light and the minimum reflectance was closed to 400-413 nm of violet and 670 nm of red light. During the cropping seasons, reflectance of near infrared changed from 14 to 55 short-wave infrared changed from 7 to 31% and middle-wave infrared changed from 4 to 24%. Although the pattern of reflectance spectrum was similar between cropping seasons， differences existed in different wavebands, both in wavelengths and reflectance, due to the contrast climatic environment during the growing periods. The variations in spectral curves between growth stages and cropping seasons were the combination effects of differences in coloration, morphology and architecture of canopy. Seasonal changes in reflectance at green light maximum，red light minimum, and near infrared peak were curvilinear. The spectral indices resulted from these spectral characteristics followed the changes of these parameters along plants development. Among them，the red edge inflection point has the potential as an index for classifying developmental stages of rice plants.