A STUDY ON THE EFFECTS OF VIEWING ANGLE VARIATION IN SUGARCANE RADIOMETRIC MEASURES

• Published in: Boletim de Ciências Geodésicas 2018-01, Vol.24 (1), p.85-97
• Main Authors: Moriya, Érika Akemi Saito, Imai, Nilton Nobuhiro, Tommaselli, Antonio Maria Garcia
• Format: Article
• Language: English
• Subjects: Algorithms; Angles (geometry); Anisotropy; Bidirectional reflectance; Detection; Distribution functions; Earth science; Ethanol; GEOCHEMISTRY & GEOPHYSICS; Image acquisition; Mosaics; Reflectance; REMOTE SENSING; Spectra; Spectral reflectance; Spectral signatures; Spectrum analysis; Studies; Sugarcane; Vegetation cover; Viewing; Wavelengths
• ISSN: 1413-4853; 1982-2170; 1982-2170
• DOI: 10.1590/s1982-21702018000100007

Remote Sensing techniques, such as field spectroscopy provide information with a large level of detail about spectral characteristics of plants enabling the monitoring of crops. The aim of this study is to analyze the influence of viewing angle in estimating the Bidirectional Reflectance Distribution Function (BRDF) for the case of sugarcane. The study on the variation of the spectral reflectance profile can help the improvement of algorithms for correction of BRDF in remote sensing images. Therefore, spectral measurements acquired on nadir and different off-nadir view angle directions were considered in the experiments. Change both anisotropy factor and anisotropy index was determined in order to evaluate the BRDF variability in the spectral data of sugarcane. BRDF correction was applied using the Walthall model, thus reducing the BRDF effects. From the results obtained in the experiments, the spectral signatures showed a similar spectral pattern varying mainly in intensity. The anisotropy factor which showed a similar pattern in all wavelengths. The visual analysis of the spectral reflectance profile of sugarcane showed variation mainly in intensity at different angles. The use of Walthall model reduced the BRDF effects and brought the spectral reflectance profiles acquired on different viewing geometry close to nadir viewing. Therefore, BRDF effects on remote sensing data of vegetation cover can be minimized by applying this model. This conclusion contributes to developing suitable algorithms to produce radiometrically calibrated mosaics with remote sensing images taken by aerial platforms. Resumo: Técnicas de Sensoriamento Remoto, como a espectroscopia de campo fornecem informações mais detalhadas das características espectrais das plantas permitindo um melhor acompanhamento da cultura. O objetivo deste trabalho é analisar a influência do ângulo de visada na estimativa da Função de Distribuição de Reflectância Bidirecional (FDRB) no caso da cana-de-açúcar. Nesse sentido, foram avaliadas as variações decorrentes da mudança no ângulo de visada e conforme a região do espectro eletromagnético. O estudo da variação das curvas espectrais permite auxiliar o desenvolvimento de algoritmos para correção da FDRB em imagens de sensoriamento remoto. Portanto, as medições espectrais em ângulos no nadir e fora do nadir foram consideradas nos experimentos. O fator de anisotropia e o índice de anisotropia foram determinados com o objetivo de avaliar a variabilidade do