Spectral Mixture Analysis of Inland Tropical Amazon Floodplain Waters Using EO-1 Hyperion

Abstract

The optical properties of the Amazon waters are controlled by the so called optically active substances which can be represented by the load of suspended and dissolved substances in water, and phytoplankton. The water composition undergoes intense variations along the year, as a response to the seasonal exchange of water between the Amazon River and its floodplain. The present study evaluates the use of spaceborne hyperspectral image, collected by EO-1 Hyperion sensor, for the spectral mapping of water composition in the Amazon floodplain. Hyperion data was acquired with 30 m spatial resolution (10 nm bandwidth) on June 23, 2005 at the end of the high water season, over a site located upstream the confluence of Amazon and Tapajos rivers. A field campaign was carried out between June 23 and 29, 2005 to collect almost simultaneous ground data. A spectral mixture analysis of the Hyperion surface reflectance data, in the visible-near-infrared range of 457 -885 nm, was conducted to identify spectrally distinct endmembers of Amazon floodplain water types and map their fractional abundances. The results show that the fractional endmember abundances correlate significantly with measured concentrations of optically active substances. Important non-linear spectral mixture effects were observed in the complex Amazon floodplain waters, which should be accounted for to achieve better predictive sub-pixel characterization of water composition.