William D. Middleton

Tomb Use and Reuse in Oaxaca, Mexico

Recently, a major debate has arisen over the interpretation of Monte Alban Tomb 7. This debate hinges, in part, on whether the skeletal assemblage comprised either primary or secondary burials. Previous studies of Mesoamerican mortuary practices generally have recognized only primary and secondary burials in tombs. Findings from a recently excavated tomb in Ejutla, Oaxaca, demonstrate that a third possibility exists: multiple-interment tomb assemblages. These assemblages result from a process we call “ongoing tomb use.” Based on comparisons with the Ejutla interments we propose that the Monte Alban Tomb 7 assemblage may have resulted from ongoing tomb use.

Hyperspectral clustering and unmixing for studying the ecology of state formation and complex societies

This project is an application of hyperspectral classification and unmixing in support of an ongoing archaeological study. The study region is the Oaxaca Valley located in the state of Oaxaca, Mexico on the southern coast. This was the birthplace of the Zapotec civilization which grew into a complex state level society. Hyperion imagery is being collected over a 30,000 km2 area. Classification maps of regions of interest are generated using K-means clustering and a novel algorithm called Gradient Flow. Gradient Flow departs from conventional stochastic or deterministic approaches, using graph theory to cluster spectral data. Spectral unmixing is conducted using the RIT developed algorithm Max-D to automatically find end members. Stepwise unmixing is performed to better model the data using the end members found be Max-D. Data are efficiently shared between imaging scientists and archaeologists using Google Earth to stream images over the internet rather than downloading them. The overall goal of the project is to provide archaeologists with useful information maps without having to interpret the raw data.

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

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 ground-truth 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.

Spectral library generation for hyperspectral archaeological validation

Fractional abundance maps have been produced from Hyperion hyperspectral data over Oaxaca, Mexico, by applying a new spatially adaptive spectral unmixing algorithm. The goal of this research is to produce land-use maps for aiding archaeologists studying the Zapotec civilization. However, to correlate the fractional abundance maps generated from the HSI image processing, a relationship between the known materials located in Oaxaca, Mexico, and the spectral profiles of these materials must be established. A field campaign during December 2011, (the dry season in Oaxaca) took place for the explicit task of obtaining spectral profiles of the most common materials found in the region. Ground-truth information was collected for three Oaxaca valleys (Tlacolula, Yanhuitlan, and Ycuitla). Common materials and associated regions were recorded and material samples were collected at many of these locations. Laboratory reflectance spectral profiles of the collected material samples are measured after the field campaign using a FieldSpec Pro. Wavelength ranges of the FieldSpec Pro spanned 350-2500nm matching that of the hyperspectral imagery collected from the Hyperion sensor on board the EO-1 satellite. GIS maps of the three valleys in Oaxaca, Mexico, are used to identify where these samples were collected and correspond to the laboratory measured material samples. The spectral library entries obtained correspond to bare soils, senescent agricultural vegetation, senescent natural vegetation, and terra cotta tile.