Tracking Human-Induced Landscape Disturbance at the Nasca Lines UNESCO World Heritage Site in Peru with COSMO-SkyMed InSAR

Francesca Cigna,Deodato Tapete

doi:10.3390/rs10040572

Abstract

The “Lines and Geoglyphs of Nasca and Palpa” in Peru are among the most well-known UNESCO World Heritage Sites globally, and an exemplar of site where heritage assets cannot be separated from their natural and anthropogenic environment. The site is exposed to interactions with natural processes, as well as human presence. In this work, 3-m resolution synthetic aperture radar (SAR) StripMap HIMAGE HH-polarised scenes acquired by the X-band COSMO-SkyMed constellation are exploited to track two events of human-induced landscape disturbance that occurred in December 2014 and January 2018. Pre-, cross-, and post-event interferometric SAR (InSAR) pairs characterised by small temporal and normal baselines allow the detection of temporal decorrelation associated with the two events, the extent and time reference of which match with online photographic and video evidence, published literature, web news, and press releases by the Ministry of Culture in Peru. Further elements enhancing the understanding of the 2018 event come from 10-m resolution Sentinel-2B satellite data that reveal the occurrence of apparent changes of surface reflectance due to uncovering of the light grey-yellow clay underneath the darker pebble constituting the fragile surface of the Pampa de Jumana. This scientific study confirms that SAR imagery archives, such as those being built by COSMO-SkyMed for Nasca, prove valuable for the retrospective analysis and digital recording of human-induced landscape disturbance events from space. These archives therefore act as essential sources of geospatial information on the conservation history of heritage sites and assets.

Highlights

The “Lines and Geoglyphs of Nasca and Palpa” are a Peruvian archaeological heritage site located in the Libertadores-Wari Region in southern Peru, nearly 400 km south of Lima (Figure 1), that were declared a UNESCO World Heritage Site (WHS) and, as such, inscribed on the World Heritage List in 1994
The objective of this study was to demonstrate the feasibility and performance of change detection based on interferometric SAR (InSAR) coherence to create digital records of condition assessment of heritage assets in circumstances of known human-induced landscape disturbance
This objective was achieved via an analysis of the synthetic aperture radar (SAR) signal recorded in a regular, frequent, and consistent COSMO-SkyMed acquisition schedule over two selected areas of the Nasca Lines WHS in Peru that were affected by site disturbance events in 2014 and 2018

Summary

Introduction

The “Lines and Geoglyphs of Nasca and Palpa” (hereinafter called “Lines”) are a Peruvian archaeological heritage site located in the Libertadores-Wari Region in southern Peru, nearly 400 km south of Lima (Figure 1), that were declared a UNESCO World Heritage Site (WHS) and, as such, inscribed on the World Heritage List in 1994. The Lines are probably among the most well-known WHS globally, and an exemplar of a site where heritage assets cannot be separated from their natural and anthropogenic environment. This character is explicitly stated in the definition of the WHS integrity: “The Lines and Geoglyphs of Nasca and Pampas de Jumana, with their protection area that extends over 75,358.47 Ha, are well defined and include all physical aspects that convey the Outstanding Universal Value of the property, including its surrounding landscape with which they make up an indivisible unit in a harmonious relationship that has survived virtually unaltered over the centuries” [3]. There is a history of events due to human action that have been reported in official reports, press releases of the Ministry of Culture of Peru, media, and published literature, for the surface damage and landscape disturbance they caused at various locations of this hugely wide WHS (e.g., [7,8,9,10])

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