Athos Agapiou

Evaluation of Broadband and Narrowband Vegetation Indices for the Identification of Archaeological Crop Marks

Several studies in the past have examined the spectral capability of multispectral and hyperspectral imagery for the identification of crop marks, while recent studies have applied different vegetation indices in order to support remote sensing archaeological applications. However, the use of vegetation indices for the detection of crop marks lacks in accuracy assessment and critical evaluation. In this study, 71 vegetation indices were indexed, from the relevant bibliography, and evaluated for their potential to detect such crop marks. During this study, several ground spectroradiometric campaigns took place, in a controlled archaeological environment in Cyprus, cultivated with barley crops, during a complete phenological cycle (2011-2012). All vegetation indices, both broadband and narrowband, were evaluated for their separability performance, and the results were presented through tables and diagrams. In the end, the use of more than one vegetation index is suggested in order to enhance the final results. In fact, several not widely used vegetation indices are suggested and evaluated using both Landsat TM and EO-1 Hyperion images.

Spectral sensitivity of ALOS, ASTER, IKONOS, LANDSAT and SPOT satellite imagery intended for the detection of archaeological crop marks

This study compares the spectral sensitivity of remotely sensed satellite images, used for the detection of archaeological remains. This comparison was based on the relative spectral response (RSR) Filters of each sensor. Spectral signatures profiles were obtained using the GER-1500 field spectroradiometer under clear sky conditions for eight different targets. These field spectral signature curves were simulated to ALOS, ASTER, IKONOS, Landsat 7-ETM+, Landsat 4-TM, Landsat 5-TM and SPOT 5. Red and near infrared (NIR) bandwidth reflectance were re-calculated to each one of these sensors using appropriate RSR Filters. Moreover, the normalised difference vegetation index (NDVI) and simple ratio (SR) vegetation profiles were analysed in order to evaluate their sensitivity to sensors spectral filters. The results have shown that IKONOS RSR filters can better distinguish buried archaeological remains as a result of difference in healthy and stress vegetation (approximately 1–8% difference in reflectance of the red and NIR band and nearly 0.07 to the NDVI profile). In comparison, all the other sensors showed similar results and sensitivities. This difference of IKONOS sensor might be a result of its spectral characteristics (bandwidths and RSR filters) since they are different from the rest of sensors compared in this study.

The Importance of Accounting for Atmospheric Effects in the Application of NDVI and Interpretation of Satellite Imagery Supporting Archaeological Research: The Case Studies of Palaepaphos and Nea Paphos Sites in Cyprus

This paper presents the findings of the impact of atmospheric effects when applied on satellite images intended for supporting archaeological research. The study used eleven multispectral Landsat TM/ETM+ images from 2009 until 2010, acquired over archaeological and agricultural areas. The modified Darkest Pixel (DP) atmospheric correction algorithm was applied, as it is considered one of the most simple and effective atmospheric corrections algorithm. The NDVI equation was applied and its values were evaluated before and after the application of atmospheric correction to satellite images, to estimate its possible effects. The results highlighted that atmospheric correction has a significant impact on the NDVI values. This was especially true in seasons where the vegetation has grown. Although the absolute impact on NDVI, after applying the DP, was small (0.06), it was considered important if multi-temporal time series images need to be evaluated and cross-compared. The NDVI differences, before and after atmospheric correction, were assessed using student’s t-test and the statistical differences were found to be significant. It was shown that relative NDVI difference can be as much as 50%, if atmosphere effects are ignored. Finally, the results had proven that atmospheric corrections can enhance the interpretation of satellite images (especially in cases where optical thickness of water vapour is minimized ≈ 0). This fact can assist in the detection and identification of archaeological crop marks. Therefore, removal of atmospheric effects, for archaeological purposes, was found to be of great importance in improving the image enhancement and NDVI values.

Vegetation indices and field spectroradiometric measurements for validation of buried architectural remains: verification under area surveyed with geophysical campaigns

This study presents an alternative approach for detecting possible archaeological crop marks using medium multitemporal resolution satellite data and field spectroscopy measurements during a whole phenological cycle of the crops and normalized difference vegetation index (NDVI) values. Geophysical surveys have been carried out on areas where archaeological remains with crops existed for validation and verification. The study presents the results obtained by applying the NDVI for a series of multitemporal Landsat TM/ETM+ images acquired from June 2009 to June 2010, intended for detecting archaeological crop marks in the Paphos District area in Cyprus. The results were validated using in situ spectroradiometric measurements using the GER 1500 field spectroradiometer. The authors compared the NDVI values between three sites in which barley crop is cultivated during a complete phenological cycle. The first site was a known archaeological area (Site 1), while the other two sites were healthy cultivated areas (Sites 2 and 3). The sites had similar soil and climatic characteristics. It has been found that during the phenological cycle, the NDVI plot for Site 1 was significantly different from the healthy areas. The detection of possible archaeological areas was based on anomalies observed and measured on vegetation indices, during the phenological cycle, of the “stressed” barley compared to healthy “nonstressed” barley in all three sites. At the end of the life cycle (after June 2010), the local authorities commenced excavation work at Site 1. Buried archaeological remains, 20 to 30 cm below ground surface were found. Anomalies found in the NDVI phenological cycle, as in Site 1, could be used for detecting areas with buried archeological remains.

Orthogonal Equations of Multi-Spectral Satellite Imagery for the Identification of Un-Excavated Archaeological Sites

This paper aims to introduce new linear orthogonal equations for different satellite data derived from QuickBird; IKONOS; WorldView-2; GeoEye-1, ASTER; Landsat 4 TM and Landsat 7 ETM+ sensors, in order to enhance the exposure of crop marks. The latest are of significant value for the detection of buried archaeological features using remote sensing techniques. The proposed transformations, re-projects the initial VNIR bands of the satellite image, into a new 3D coordinate system where the first component is the so called “crop mark”, the second component “vegetation” and the third component “soil”. For the purpose of this study, a large ground spectral signature database has been explored and analyzed separately for each different satellite image. The narrow band reflectance has been re-calculated using the Relative Spectral Response filters of each sensor, and then a PCA analysis was carried out. Subsequently, the first three PCA components were rotated in order to enhance the detection of crop marks. Finally, all proposed transformations have been successfully evaluated in different existing archaeological sites and some interesting crop marks have been exposed.

Exploring natural and anthropogenic risk for cultural heritage in Cyprus using remote sensing and GIS

Abstract On site observation is the most common way of monitoring cultural heritage sites and monuments in Cyprus. However, this procedure that includes data collection, periodical observations, and multivariate risk assessment analysis is difficult to accomplish with the traditional practices and methods since it is time consuming and expensive. Furthermore, many archaeological sites and monuments are located at inaccessible areas, far away from the main road network and urban areas. Satellite remote sensing and Geographical Information Systems (GIS) can successfully confront this problem by providing the scientists with integrated monitoring of the study areas and the unique advantage to store and manipulate a large amount of spatial and attribute data simultaneously. Actually the monitoring and identification of several natural and anthropogenic hazards in the vicinity of the cultural heritage sites in Cyprus, seems to be one of the main priorities of its governmental and municipal authorities. This study aims to integrate both satellite remote sensing techniques and GIS in a multidisciplinary approach, for monitoring anthropogenic and natural hazards with the use of archived and up-to-date multitemporal remotely sensed images in the study area, namely in areas nearby cultural heritage sites and monuments in Cyprus. In this study anthropogenic hazards include urbanisation and extended land use changes in the surroundings of archaeological sites and natural hazards concern seismicity and sea erosion.

The Methodology Of Documenting Cultural Heritage Sites Using Photogrammetry, UAV And 3D Printing Techniques: The Case Study Of Asinou Church In Cyprus

As the affordability, reliability and ease-of-use of Unmanned Aerial Vehicles (UAV) advances, the use of aerial surveying for cultural heritage purposes becomes a popular choice, yielding an unprecedented volume of high-resolution, geo-tagged image-sets of historical sites from above. As well, recent developments in photogrammetry technology provide a simple and cost-effective method of generating relatively accurate 3D models from 2D images. These techniques provide a set of new tools for archaeologists and cultural heritage experts to capture, store, process, share, visualise and annotate 3D models in the field. This paper focuses on the methodology used to document the cultural heritage site of Asinou Church in Cyprus using various state of the art techniques, such as UAV, photogrammetry and 3D printing. Hundreds of images of the Asinou Church were taken by a UAV with an attached high resolution, low cost camera. These photographic images were then used to create a digital 3D model and a 3D printer was used to create a physical model of the church. Such a methodology provides archaeologists and cultural heritage experts a simple and cost-effective method of generating relatively accurate 3D models from 2D images of cultural heritage sites.

Evaluating the Potentials of Sentinel-2 for Archaeological Perspective

The potentials of the forthcoming new European Space Agency’s (ESA) satellite sensor, Sentinel-2, for archaeological studies was examined in this paper. For this reason, an extensive spectral library of crop marks, acquired through numerous spectroradiometric campaigns, which are related with buried archaeological remains, has been resampled to the spectral characteristics of Sentinel-2. In addition, other existing satellite sensors have been also evaluated (Landsat 5 Thematic Mapper (TM); Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER); IKONOS; Landsat 4 TM; Landsat 7 Enhance Thematic Mapper Plus (ETM+); QuickBird; Satellite Pour l’Observation de la Terre (SPOT); and WorldView-2). The simulated data have been compared with the optimum spectral regions for the detection of crop marks (700 nm and 800 nm). In addition, several existing vegetation indices have been also assessed for all sensors. As it was found, the spectral characteristics of Sentinel-2 are able to better distinguish crop marks compared to other existing satellite sensors. Indeed, as it was found, using a simulated Sentinel-2 image, not only known buried archaeological sites were able to be detected, but also other still unknown sites were able to be revealed.

Cultural heritage management and monitoring using remote sensing data and GIS: the case study of Paphos area, Cyprus

Cultural heritage (CH) sites are threatened from a variety of natural and anthropogenic factors. Innovative and cost effective tools for systematic monitoring of landscapes and CH sites are needed to protect them. Towards this direction, the article presents a multidisciplinary approach, based on remote sensing techniques and Geographical Information System (GIS) analysis, in order to assess the overall risk in the Paphos district (Cyprus). Paphos region has a great deal of archaeological sites and isolated monuments, which reflect the long history of the area, while some of them are also listed in the UNESCO catalogue of World Cultural Heritage sites. Several natural and anthropogenic hazards have been mapped using different remote sensing data and methodologies. All data were gathered from satellite images and satellite products. The results from each hazard were imported into a GIS environment in order to examine the overall risk assessment based on the Analytic Hierarchy Process (AHP) methodology. The results found that the methodology applied was effective enough in the understanding of the current conservation circumstances of the monuments in relation to their environment as well as predicting the future development of the present hazards.

Risk assessment of cultural heritage sites clusters using satellite imagery and GIS: the case study of Paphos District, Cyprus

This paper aims to assess the risk of natural and anthropogenic hazards for cultural heritage in Cyprus by integrating multi-temporal GIS and earth observation analysis, in the area of Paphos District. The work presented here attends to re-evaluate previous results from earth observations and GIS analysis and go a step forward targeting more reliable outcomes for cultural heritage management. The scope of the paper was to develop a more accurate methodology for risk assessment against natural and anthropogenic hazards (e.g., soil erosion; urban expansion), based on homogeneous clustering of the monuments under consideration. The accomplished assessment approach, being lopsided and generic, cannot be applied across the board and undistractedly for cultural heritage management of all types of monuments of the district. Instead, the proposed clustering of monuments based on a variety of parameters is taking into consideration characteristics of their immediate environment, resulting rational local-based outcomes more useful for monuments and sites safeguarding and for prevention measurements. For each one of the five clusters of monuments located in the Paphos District, an analytical hierarchy process (AHP) method was followed in order to address the individual and unique characteristics of the monuments and sites within the same cluster area. Subsequently, the weight factors from these clusters were interpolated to the whole district, prior to the application of the overall AHP risk assessment. Ultimately, the results were compared with the overall AHP method applied for the entire Paphos District, indicating that the proposed methodology can be more accurate and realistic for the different groups of the monuments.