影響甘藷葉片光譜特徵因子之研究

Study on the factors affecting reflectance spectra of sweet potato leaves

王珮珊(Pei-Shan Wang)

指導教授 ： 張新軒

共同指導教授 ： 楊棋明 ； 蔡養正(Yang-Zenq Tsai)

國立臺灣大學/生物資源暨農學院/農藝學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.00649

摘要

本篇論文研究主題為利用光譜儀量測四種不同處理（新鮮、新鮮乾燥、脫色含水、脫色乾燥）的三種品系不同顏色（綠色、紫色、黃色）甘藷葉片，所得之吸收、穿透、反射光譜，其與葉片厚薄、水分含量、色素含量間的關係，並以所測得之反射率（R705與R750）計算常態化差異植生指數（NDVI）。
三種品系不同顏色甘藷葉片的葉片厚度，在可見光中與吸收光譜成正比，與穿透及反射光譜成反比，而在近紅外光中與吸收及反射光譜成正比，與穿透光譜成反比。
新鮮甘藷葉片中的水分含量減少，使吸收光譜增加，但經脫色處理後，吸收光譜因水分含量增加而上升。在新鮮葉片中，水分含量增加，穿透光譜亦隨之升高，但在脫色葉片中，含水葉片反而減少穿透率。反射光譜在近紅外光中與水分含量成正比，而在可見光中，綠色及紫色葉片反射光譜與水分含量成反比，但黃色葉片的反射光譜與水分含量成正比。將三種顏色甘藷葉片脫色後，反射光譜與水分含量成正比。
色素對三種顏色甘藷葉片的吸收、穿透、反射光譜影響極大，新鮮甘藷葉片在約675nm處的吸收值與葉綠素含量成正比，其中紫色甘藷葉因含有多量花青素，故在550nm處亦有強吸收。葉片脫色與否，影響葉片穿透率，若將色素除去，葉片穿透率增加，使其利用光的能力大幅下降。另外，將反射光譜經一次微分所得之反射率曲線，可看出色素對反射光譜的影響，當葉綠素含量減少時，其位於700nm處的波峰向短波長處移動。
利用反射率R750及R705計算差異化植生指數（NDVI），其與葉綠素及類胡蘿蔔素的相關性極高，R2值為0.89-0.95，可用以估計葉片之色素含量。

關鍵字

反射率 ； 常態化差異植生指數 ； 相對穿透值 ； 甘藷 ； 相對吸收值

並列摘要

The subject of this study was to utilize a spectrophotometer to measure the fresh, fresh-dry, depigment and depigment-dry sweet potato leaves. Leaf color of three sweet potato varieties included green, purple and yellow. The absorbance, transmittance and reflectance spectra of three sweet potato varieties leaves were measured. Explored the relationships between spectra and leave thickness, water content and pigment concentration. Calculated the normalized difference vegetation index（NDVI）with the reflectance at 705nm and 750nm.
The thickness of three sweet potato varieties leaves was positively correlated with the absorbance, but negative to the transmittance and reflectance in the visible light. In NIR, leaf thickness was positive to the absorbance and reflectance, negative to the transmittance.
The absorbance and transmittance spectra of fresh leaves were increased with the decreasing mesophyll water content. The absorbance spectra of depigmented leaves were increased with the increasing water content. The transmittance spectra of depigmented leaves were decreased with the increasing water content. The reflectance spectra were positively correlated with water content in NIR. In visible light, the reflectance of ‘Green’ and ‘Purple’ were negatively correlated with water content, but the ‘Yellow’ were positive. The reflectance of depigmented leaves was negatively correlated with water content.
Pigments affected absorbance, transmittance and reflectance spectra of sweet potato leaves. The relative absorbance at 675nm in fresh leaves was positively correlated with chlorophyll content. The ‘Purple’ sweet potato leaves had abundant anthocyanin, its absorbance peak was around 550nm. The results also revealed that leaf transmittance was affected by depigmentation.
Otherwise, the first order of reflectance indicated that reflectance spectra were affect by pigments. The peak around 700nm moved to the shorter wave when the chlorophyll content decreased.
Computed the NDVI with the reflectance at R750 and R705. The NDVI was significantly correlated with leaf pigment such as chlorophyll and carotenoids, the R2 were 0.89-0.95. It can possibly be used for prediction of leaf pigment content.

並列關鍵字

transmittance ； absorbance ； sweet potato ； reflectance ； NDVI

參考文獻

李良。（1994）。甘藷。雜糧作物各論。臺灣區雜糧發展基金會。第1327-1477頁。

汪呈因。（1966）。甘藷。食用作物學。國立編譯館。第446-477頁。

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