Narrow band spectral indexes for chlorophyll determination in soybean canopies [Glycine max (L.) Merril]

Abstract

Photosynthetic pigments are essential for plant development. Quantifying these pigments in great extensions of agricultural crops is an important objective in remote sensing for agricultural purposes. This information can be used to produce a more accurate estimation of the physiological state of the vegetation, for species discrimination and productivity estimation. The aim of the present study was to (a) evaluate the potential for estimating chlorophyll content of crop canopies, using narrow band spectral indexes, and (b) in this respect compare the performances of NDVI (a multispectral wide band index) and two narrow band vegetation indexes (R 750/700 and R 750/550 ). Experiments were carried out under greenhouse conditions whereby soybean [Glycine max (L.), Merril] was monitored with a high-resolution spectroradiometer (10 nm at 365-1,126 nm range) during the phenological cycle of the crop. Chlorophyll (a, b and total) contents were determined weekly in the laboratory. A statistical correlation analysis was performed between narrow band spectral indexes against chlorophyll content and r 2 coefficients near 0.84 were obtained. For NDVI r 2 was around 0.51. These analyses showed that R 750/700 and R 750/550 ratios are very useful indexes for chlorophyll determination and very effective compared with NDVI (one of the wide band indexes widely used). Thus, it can be stated that hyperspectral remote sensing has great potential for providing a reliable estimate of photosynthetic pigment content at the canopy level through evaluated indexes and other such indexes that might arise. Thus, further studies should be carried out for evaluating other indexes at the canopy level, both in the laboratory and under field conditions, using spectroradiometers and hyperspectral images, aimed at providing information for agricultural purposes. Key words: canopy chemistry, hyperspectral remote sensing, remote sensing in agriculture, spectroradiometry. Índices hiperespectrais de vegetação para a determinação do conteúdo de clorofila em dosséis de soja [Glycine max (L.) Merril]:Os pigmentos fotossintéticos são essenciais ao desenvolvimento das plantas e sua quantificação em grandes extensões de culturas agrícolas é uma das metas mais importantes do sensoriamento remoto aplicado à agricultura. Essa informação pode ser utilizada para determinar, mais precisamente, o estado fisiológico das plantas, discriminar as espécies plantadas e estimar a produtividade. O presente trabalho teve como objetivos: (a) avaliar o acerto da estimativa do conteúdo de clorofila em dosséis de culturas, usando índices espectrais de bandas estreitas, e (b) comparar os desempenhos do Índice de Vegetação Diferença Normalizada (NDVI) em relação a dois índices de bandas estreitas (R 750/700 e R 750/550 ). Desenvolveu-se um experimento em condições de casa de vegetação cuja cultura da soja [Glycine max (L.) Merril] foi monitorada, durante o seu ciclo fenológico, com um espectrorradiômetro de alta resolução espectral (10 nm no intervalo de 365 a 1.126 nm). Determi...

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