Comparison of hyperion spectral unmixing endmembers to material spectral profiles from Oaxaca, Mexico

Abstract

As part of a study of the ecology of the ancient Mesoamerican Zapotex state, endmember abundance maps of a large portion of the state of Oaxaca, Mexico, were generated using Hyperion imagery and a spatially adaptive spectral unmixing approach. However, the ecological diversity of Oaxaca makes it difficult to identify the materials the endmembers correspond to without groundtruth data. Therefore, during December 2011 ground-truth data and samples were collected from three different valleys in Oaxaca (Tlacolula, Yanhuitlan, and Yucuita). A total of 24 different soil and plant samples and one terra cotta tile sample were collected from these valleys. These samples include white caliché rocks and soil, grey basalt volcanic rocks, red iron-stained soils, yellow iron-stained soils, and several different senescent plant samples. The reflectance spectra of these samples were acquired through laboratory measurements using an Analytical Spectral Device FieldSpec Pro covering 400-2500nm. Concurrently to the laboratory measurements, endmember abundance maps were generated using a spatially-adaptive spectral unmixing algorithm and Hyperion hyperspectral imagery of the Tlacolula Valey.A comparison of the Hyperion endmembers to the laboratory sample reflectance measurements is performed to determine which of the Hyperion endmemberss result from a single type and which from a linear mixture of multiple materials. It is shown that of the eight derived endmembers, seven appear to be mixtures of multiple materials.