Amplitude change detection with ENVISAT ASAR to image the cultural landscape of the Nasca Region, Peru

Synthetic aperture radar (SAR) amplitude information from ENVISAT C-band advanced SAR (ASAR) data was used to analyse the cultural landscape of the Nasca region, southern Peru. A multispatial environmental analysis was performed over the whole drainage basin of the Rio Grande, by extracting the radar backscattering coefficient (σ0) of both natural and anthropogenic features between 2003 and 2005. Co-registration of the ASAR scenes to a single master resulted in precisions of less than 0.1 pixels along both the range and azimuth directions. Four different products were generated based on the co-registered ASAR stack: (i) temporally averaged radar signatures of the targets between 2003 and 2005; (ii) time series of spatially averaged radar signatures within selected areas of interest; (iii) amplitude change detection products based on (iii) image ratios and (iv) RGB colour composites between different scenes. Comparisons of annual and seasonal records through amplitude change detection maps highlighted σ0 changes over the floodplains of the Rio Ingenio and Rio Nazca, which correlate well with evidence from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data acquired in 2003, 2004 and 2007. Inferences about land use and soil conditions were retrieved from the σ0 change patterns, thereby proving the capability of this approach to support landscape evolution studies, even with SAR imagery of medium resolution (~30 m). Our results also demonstrated actual potential for monitoring mass movements and land surface processes, to assess the susceptibility of archaeological heritage and cultural landscape to natural hazards

Prospection and monitoring of the archaeological heritage of Nasca, Peru, with ENVISAT ASAR

The processing method based on synthetic aperture radar (SAR) amplitude information presented by Cigna et al. (2013, this issue) was used to extract the backscattering coefficient (σ0) from ENVISAT advanced SAR (ASAR) scenes to investigate the archaeological heritage of the Nasca region, southern Peru. Average backscattering and σ0 time series in 2003–2007 were obtained for some of the most famous groups of the Nazca Lines, as well as for the adobe structures of the Ceremonial Centre of Cahuachi, and allowed the recognition of anthropogenic features on arid and bare soil. Despite the expected constraints due to the medium spatial resolution of the ASAR scenes (~30 m), some features related to the Nasca ancient aqueduct systems (puquios) were detected, and water level changes were inferred from amplitude change detection maps and σ0 time series. The SAR-based prospection results were also compared with a vegetation index derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for 2003, 2004 and 2007. The changes observed over Cahuachi and the neighbouring archaeological mounds are then discussed in light of the recent conservation history of the site and the contemporary archaeological excavations. The research opens interesting perspectives for routine use of SAR data for purposes of archaeological prospection and condition monitoring in (semi-)arid and desert regions