## 4 Conclusions  
The objective of this study was to demonstrate the feasibility and performance of change detection based on 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 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. The method was intentionally tested on two different temporal scales to prove the advantages offered by a high-resolution SAR archive for both retrospective analysis of past incidents (e.g., December 2014) and substantiation of events soon after they have occurred (e.g., January 2018). Because the COSMO-SkyMed constellation is tasked to acquire SAR images over the Nasca Lines with a predefined observation scenario at a regular temporal sampling, it is possible to create multiple InSAR coherence pairs between pre- and post-event images that allow the optimisation of \(B_{t}\) and \(B_{p}\) combinations in order to minimize temporal and geometric decorrelation. In the case of the site disturbance that happened in January 2018, the various cross-event InSAR pairs that were generated and analysed led to a positive redundancy of information on the temporal decorrelation caused by the disturbance. In the multitemporal domain, the analysis allowed the enhancement of the spatial patterns of low-coherence areas (\(\gamma<0.4\)) where the tire marks were left by the truck against a clean pre-event baseline InSAR record. This result has been achieved in this study under different SAR imaging conditions than the common single-pair approach that is used in change detection analysis. Usually, change detection of a known event is carried out by acquiring an ad hoc image soon after (or, if possible, even during) the event of interest, and by relying on the temporal granularity that is allowed by the availability of an archive image already acquired before the event. Typically, this is the only option, unless the study area is already covered by a consistent and abundant SAR archive or is a known hotspot that is regularly monitored. In Nasca, on the other hand, the study benefitted from a different change detection paradigm. A COSMO-SkyMed high-resolution SAR time series is being acquired since 2011, and consequently, the probability that unexpected events can be captured in a timely manner in the images is higher, regardless of when the data analysis and creation of the associated digital record are undertaken. The experiments described in this paper prove that growing SAR image archives, such as that currently being built by the COSMO-SkyMed constellation in Nasca, can be great assets towards a sustainable approach of heritage conservation. In particular, they can be extremely valuable in situations where the site managers themselves acknowledge the practical difficulties of monitoring widespread heritage assets and huge cultural landscapes (see [(22)] with specific regard to the Nasca Lines WHS). In summary, growing and consistent SAR archives provide a wider spectrum of imaging solutions to capture events of site disturbance, reduce the constraints due to insufficient or missing data, and enable the operators to create digital records from remote and at any time. These are all properties of sustainability, and contribute towards sustainable archaeology and the conservation of cultural heritage sites. On the other side, the prerequisites for effective exploitation of these archives are knowledge of the events, maintenance of the archives, and training of the operators to use and interpret these space-borne data and their derived products. Project carried out using COSMO-SkyMed(r) Products, (c) of the Italian Space Agency (ASI), delivered under a licence to use by ASL VHR imagery (c 2018 DigitalGlobe) was analysed in Google Earth Pro.