Multi-temporal archaeological and environmental prospection in Nasca (Peru) with ERS-1/2, ENVISAT and Sentinel-1A C-band SAR data

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1 12-13 November 215 ESA-ESRIN, Frascati (Rome), Italy Day 1 Session: Historical Landscapes and Environmental Analysis Multi-temporal archaeological and environmental prospection in Nasca (Peru) with ERS-1/2, ENVISAT and Sentinel-1A C-band SAR data Francesca Cigna (1,2), Deodato Tapete (1,2), Rosa Lasaponara (2), Nicola Masini (3) (1) (2) (3)

2 Region of Interest Nazca civilization (2 BC 6 AD) N Palpa Cahuachi Atarco Nazca lines Rio Taruga Nazca 1 km

3 Archaeological heritage Lines and geoglyphs of Nasca and Pampas de Jumana Ceremonial Centre of Cahuachi Aqueducts networks and drainage galleries (puquios) and reservoirs (ojos)

4 Climate conditions Nasca Palpa Temperature Precipitation Temperature Source: Precipitation Climate: desert (Rio Grande valley) Precip.: virtually no rainfall during the year (tot. 4 mm per year) Temp.: 2.6 C (Palpa) and 2.9 C (Nasca) on average (Feb.-Mar. the warmest; July the coldest)

5 ESA & DLR Nasca projects Project id.1173 Archaeological and environmental studies in the Nasca region (Southern Peru) using multi-temporal C- and L-band SAR imagery Objectives Change detection (evolution of the Rio Nasca catchment basin) Archaeological surveying (puquios, buried structures) Ground and structural deformation analysis and looting monitoring Environmental assessment ITACA Italian mission of heritage Conservation and Archaeogeophysics LASAPONARA & MASINI (211) LASAPONARA et al. (211)

6 Satellite radar data at MR ERS-1/2 SAR ImageMode 2 scenes, desc. ( ) 8 scenes, asc. (21-211) ENVISAT ASAR ImageMode IS2 15 scenes, desc. (23-25) 5 scenes, asc. (25-27) ALOS PALSAR scenes 3 FineBeam, Dual Pol. (27-28) ASAR imagery Wavelength (λ): 5.6cm Frequency (f): 5.3GHz Look angle (θ): 22.8 Orbit incl. (α): 12.9 Repeat cycle: 35 days Satellite altitude: 79 km Pixel spacing: 8m (slant range) Ground resolution: ~25-3 m ENVISAT asc Track 175 Frame 6893 ENVISAT desc Track 311 Frame 395 N α α N

7 Satellite data processing Level (raw) IM data SLC MLI Slaves Range/Doppler sequence SLCs ASTER GDEM V2 Radiometric calibration Calibrated SLCs Multi-looking Master ASTER GDEM MLIs Co-registration Resampled SLCs & MLIs Resampled MLIs Derived products Geocoding Spatio-Temporal analysis of the data Refined lookup table GTC MLIs Derived products Geocoding GTC MLIs & Derived products (map geometry) GTC derived products

8 Radar signatures σ [23-25] Normalized stdv σ [23-25] Average backscattering coefficient Normalized temporal variability Groundwater fluctuations and cropland changes along river plains Alterations of local morphology due to mass movements σ t t 1 n = σ i ( t) n i = t = t 1 σ i = f (λ, pol., θ, roughness, shape, dielectric properties)

9 Radar signatures Nazca σ [23-25] Rio Nazca Pozo cocha Airport RGB ASTER [23] NIR-Red-Green σ [23-25] River courses and urban areas have higher σ than agricultural fields, dry and smooth surfaces (airport runaway and water bodies, e.g. pozo cocha) Dune ridges RGB ASTER [23] NIR-Red-Green Dune ridges Signal penetration depths are higher over the sand dunes of the Cerro Blanco, and σ is lower than over the surrounding mountain regions

10 Radar signatures RGB ASTER [23] NIR-Red-Green Geoglyphs Group 1 Geoglyphs Group 2 Reptile Panamericana Sur σ [23-25] Geoglyphs Group 1 Geoglyphs Group 2 Reptile Panamericana Sur

11 Temporal variations Comparison of temporal variability of radar returns from different surfaces Temporal history of average σ within different AOIs σ i N 1 ( t) = σ i N = AOI i= 1 ( t) t = acquisition time N = no. pixels within AOI i = i th pixel RI_1 RI_2 Agricultural fields have different backscattering properties but similar temporal variations, hence are likely to follow groundwater fluctuations over the different seasons

12 Change detection 15/11/25 Ratio 4/2/23 Rio Ingenio plain 3x3 or 5x5 spatial filtering R i σ = < R < 1 if R > 1 if σ ( t i i σ ( t k j ) ) σ ( t ) > σ ( t i j σ ( t ) < σ ( t i j i i k k ) )

13 Change detection Increased radar backscattering P4 P5 Decreased radar backscattering P1 P2 P3 P1 P2 P3 ASTER 3/5/23 P4 P5 P5 Decreased radar backscattering P1 P2 P3 ASTER 1/6/ : decreased σ along the Rio Ingenio plain, except P1-P3 (ratio over 4-5) May-Nov25: decreased soil moisture over vegetated/agricultural areas May23 vs. Jun24 (ASTER): decreased vegetation cover and soil moisture

14 Hydraulic networks SAR colour composite ASTER-derived NDVI Ancient puquios in the Taruga valley

15 Mass movements 4/2/23 15/4/23 24/6/23 RGB a a Wind/rain-driven morphological changes and mass movements cause local alterations of the backscattering coefficient b b

16 Landscape changes at regional scale Cahuachi Changes along river plains and over agricultural fields InSAR coherence cross-correlation between co-registered SLCs 1 Wind/rain-driven mass movements 24113_25524 Bperp: 5 m Btemp: 175 days

17 Landscape changes at local scale DESC mode Rio Nazca Cahuachi 2324_24113 Bperp 89 m Btemp 665 days 24113_25524 Bperp 5 m Btemp 175 days 2324_ Bperp 343 m Btemp 115 days 1 ASC mode 2512_2717 Bperp 4 m Btemp 375 days 2717_ Bperp 18 m Btemp 35 days

18 From historical to recent landscape evolution Oct. 214 Baseline pre-defined mission observation scenario IW mode VV polarization 24 days repeat cycle per pass (asc./desc.) and alternating the passes asc./desc. (i.e. areas observed every 12 days.

19 From historical to recent landscape evolution S1 GRD IW VV 25th Oct. 214

20 From historical to recent landscape evolution

21 From historical to recent landscape evolution R: 25 Oct. 214 G: 12 Dec. 214 B: 18 Mar. 215 R: 25 Oct. 214 G: 12 Dec. 214 B: 18 Mar. 215

22 Conclusions & future research ERS-1/2 and ENVISAT C-band satellite radar data imaged the recent evolution of cultural landscape in Nasca since 1997 SAR data proved capable to depict archaeological features, and to identify surface indicators of environmental changes in such a dynamic region Amplitude-based and coherence change detection reveal soil moisture and vegetation changes occurring along the river valleys Mass movements and other surface processes occur at seasonal and yearly scales across the Rio Grande catchment area Natural and anthropogenic factors expose the heritage of Nasca at risk Results with archive data show potential for environmental and archaeological studies with new Sentinel-1 imagery Future research will look at analysing the relationship between landscape evolution and climate change over the last 2+ years

23 Thanks! REFERENCES CIGNA F., TAPETE D., LASAPONARA R., MASINI N Amplitude change detection with ENVISAT ASAR to image the cultural landscape of the Nasca region, Peru. Archaeological Prospection, 2(2), TAPETE D., CIGNA F., MASINI N., LASAPONARA R Prospection and monitoring of the archaeological heritage of Nasca, Peru, with ENVISAT ASAR. Archaeological Prospection, 2(2), TAPETE D., CIGNA F., LASAPONARA R., MASINI N Investigating natural hazards in the Peruvian region of Nasca with spaceborne radar sensors. In: K. Sassa et al. (eds.), Landslide Science for a Safer Geo- Environment, 3, TAPETE D., CIGNA F., LASAPONARA R., MASINI N Multi-scale detection of changing cultural landscapes in Nasca (Peru) through ENVISAT ASAR and TerraSAR-X. In: G. Lollino et al (eds.) Engineering Geology for Society and Territory, 8, coming soon TAPETE D. & CIGNA F SAR for landscape archaeology. In: Masini N. & Soldovieri F. (eds). Sensing the Past: Geoscience and Sensing Technologies for cultural heritage. Springer. 15 pp.