Study of amazon floodplain water composition using hyperion/EO-1 and field reflectance data for the comprehension of temporal variability of optically active constituents / Estudo da composição das águas da planície amazônica por meio de dados de reflectância do sensor hyperion/EO-1 e de espectrômetro de campo visando a compreensão da variação temporal dos seus constituintes opticamente ativos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Two methodological approaches were evaluated to study the reflectance of optically active constituents using hyperspectral imagery of EO-1 Hyperion orbital sensor: a) Linear Spectral Mixture Model; and b) derivative analysis. Two Hyperion images acquired over an area located upstream of the confluence between the Amazon and the Tapajós rivers were analysed, looking towards the comprehension of the seasonal dynamic of the Amazon floodplains water composition. The first image was acquired September 16, 2001, during the period of the outflow of water from the floodplain lakes to the Amazon River, due to the lowering of its level. The second image was acquired June 23, 2005, at the end of the high water period. A field campaign was carried out between June 23 and 29, 2005 to collect radiometric and limnological data almost simultaneously the acquisition of this image. Both images were pre-processed to remove stripes of abnormal pixe ls and were converted from radiance to surface reflectance values, thus, correcting the effects of atmospheric absorption and scattering. A sequential procedure with the techniques of Minimum Noise Fraction (MNF), Pixel Purity Index (PPI) and n-dimensional visualization of the MNF feature space was employed to select endmembers, within the spectral range of 457-885 nm. A single set of endmembers was gathered to represent the following spectrally unique water masses: clear-water; dissolved organic matter; suspended sediments; and phytoplankton. The Linear Spectral Mixture Model mapped each scene in terms of the sub-pixels fractional abundances of the four endmembers. A temporal analysis allowed to verify the relative alterations in water composition, observing a general tendency of the increase in suspended sediment and phytoplankton concentrations along the floodplain towards the outflow period. From field and Hyperion image measurements obtained in 2005, during the high water period, correlation coefficients of the reflectance and first spectral derivative with the concentrations of optically active constituents were determined. By means of empirical model fits it was observed that, the first spectral derivative: in 711.7 nm, explained 80.9% of the variation of suspended inorganic sediments concentration (mg l-1); and in 691.9 nm, explained 68.3% of the variation of chlorophyll-a concentration (ug l-1). The two methods applied demonstrated peculiar potentials to characterize the composition of optically complex Amazon waters.

ASSUNTO(S)

water quality reflectância planície de inundação análise derivativa floodplain amazônia análise de mistura espectral differentiation reflectance imagens de satélite spectral mixture analysis spectroscopy espectroscopia remote sensing qualidade da água satellite imagery amazon region sensoriamento remoto

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