Satellite and close range analysis for the surveillance and knowledge improvement of the Nasca geoglyphs

Traditionally the history of remote sensing began during the First World War when aerial photography became a valuable reconnaissance tool. However, moving back more than a thousand years, the real pioneers of remote observation were probably the Nasca, a pre-Hispanic civilization living in southern Peru, between 100BC and 700 AD. They used ‘earth observation’ as a mean of cultural expression drawing the geoglyphs (known as Nasca Lines) only visible from above. These drawings were made on flat desert surface of the Pampa by removing or clearing sand or stones, to create paths for ritual functions to please the gods and create harmonious relationships between man and environment. In this paper, the Nasca geoglyphs in Pampa de Atarco, are object of remote sensing based investigations with the twofold aim to identify and characterize them as well as to analyse and monitor their fragile state of conservation, threatened mainly by vandalism and off road vehicles. The approach herein proposed includes the integration and reuse of diverse remote sensing dataset, from multispectral satellite to Unmanned Aerial Vehicle (UAV) based LSAR data and close range photogrammetry. In particular, a multidate (2002–2013) very high resolution (VHR) optical satellite dataset has been processed in the spatial and temporal domain using textural indicators, including Skewness, Principal Component Analysis (PCA), and automatic classification tools which allowed us to enhance the visibility of disturbance features and to automatically extract them. The best results in terms of enhancement and automatic extraction capability of disturbance features have been obtained by Skewness. Moreover, the reuse of UAV L SAR-based correlation map, available free of charge from NASA, provided useful information on the state of disturbance from 2013 to 2015, widening the observation time window of the VHR satellite data set from 2002 to 2013. Finally, the integrated use of satellite VHR data with UAV-based photographs and DTMs, processed using structure from motion (SfM), allowed us to characterize, identify and reconstruct the relative chronological sequence of geoglyphs thus providing new insights and opening new perspectives for archaeological studies.