RISK ASSESSMENT INTENDED FOR CULTURAL HERITAGE SITES AND MONUMENTS IN CYPRUS USING REMOTE SENSING AND GIS

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1 RISK ASSESSMENT INTENDED FOR CULTURAL HERITAGE SITES AND MONUMENTS IN CYPRUS USING REMOTE SENSING AND GIS Diofantos G. Hadjimitsis*, Athos Agapiou Department of Civil Engineering and Geomatics, Faculty of Engineering and Technology, Cyprus University of Technology, 2-6, Saripolou str., 3603, Limassol, Cyprus Apostolos Sarris Laboratory of Geophysical - Satellite Remote Sensing and Archaeo-environment, Institute Mediterranean Studies Foundation for Research & Technology, Hellas (F.O.R.T.H.), 130, ikiforou Foka str., 74100, Rethimno, Crete Keywords: Monitoring, Risk Assessment, Satellite Images, Remote Sensing, Geographical Information Systems ABSTRACT In Cyprus, monitoring cultural heritage sites and visible monuments is made mostly with on-site observations. However, this procedure which includes data collection, periodical observations for all archaeological sites or areas, and multi-analysis risk assessments is practically difficult with the existing practices and methods since it is time consuming and cost insufficient. Furthermore many archaeological sites and monuments are located at inaccessible areas. Indeed, satellite remote sensing can be used as systematic tool for monitoring cultural heritage sites, in vast areas. The monitoring and identification of several natural and anthropogenic hazards in the vicinity of the cultural heritage sites in the Cyprus is one of the main priorities of the governmental or municipal officers. Anthropogenic hazards may include building development which endangers archaeological sites and monuments, land use changes in the surrounding area of archaeological sites etc. Natural hazards can be soil erosion, landslides, forest or agricultural fires etc. This study aims to integrate both satellite remote sensing techniques and GIS for monitoring anthropogenic and natural hazards using archived and up-to-dated multi-temporal remotely sensed images at areas nearby to cultural heritage sites and monuments in Cyprus. INTRODUCTION Hazard is defined as the probability that a phenomenon, of given intensity, may occur in a defined area during a given period of time. Elements at risk include population, properties, buildings, transportation, infrastructures and economic activities [1] Despite the fact that the general guidelines for the assessment of the risk of natural disasters are stated by the United Nations Disaster Relief Organisation of UNESCO generally recommends that risk assessment be expressed in monetary terms [2], Canuti et al. (2000) however point out that in the case of cultural heritage this is not possible. Canuti et al highlight that the potentially destructive phenomena are represented as the effects of the different dynamics (e.g. landslides, floods, coastal erosion) on archaeological sites, which constitute the elements exposed to risk [1]. Remote Sensing has been widely used in other studies (e.g. natural hazards such as floods, draughts etc) for applying risk assessment in growing urban areas by using both Digital Elevation 1/11

2 Models (DEMs) and GIS in a great extent [3;4;5]. Risk assessment intented for monitoring archaeological sites and monuments has also been applied successfully in different parts of the world investigating natural and anthropogenic hazards at cultural heritage sites [6; 7;8], however further research on the appropriate post-processing algorithm for retrieving hazards is still an open question. In Cyprus, monitoring cultural heritage sites and visible monuments is made mostly with on-site observations. However, this procedure which includes data collection, periodical observations for all archaeological sites or areas, and multi-analysis risk assessments is practically difficult with the existing in-situ practices and methods since are found to be time consuming and cost insufficient. Based on the fact that several land cover changes have been taken place in the last 15 years in Cyprus due to the rapid building development, the requirement for investigating their impact in the existing cultural heritage sites is of a great importance. Due to the continuous urban activity several threats to the cultural heritage sites must be quantified and assessed. Such threats or hazards include building activity, air pollution, geological features etc. Indeed, this study aims to integrate both satellite remote sensing techniques and GIS for monitoring anthropogenic and natural hazards using archived and up-to-dated multi-temporal remotely sensed images at areas in the vicinity of cultural heritage sites and monuments in Cyprus. CASE STUDIES For the aims of the study the following archaeological sites of Cyprus all located in the southern coastal part of the island were examined: Tombs of the Kings, Nea Paphos, Palaepaphos, Kourion and Amathus. Figure 1: Tombs of the Kings (left) and Nea Paphos archaeological site (right) Figure 2: Main archaeological sites of south Cyprus (from left to right: Tombs of the Kings, Nea Paphos, Palaepaphos, Kourion and Amathus ) METHODOLOGY 2/11

3 Risk assessment Process: Generally, risk assessment process consists the following steps: identify, analyze and evaluate the risk. Indeed, the overall process of this study is consisted on the following steps: Identify the risks: for the purpose of the study both anthropogenic and natural hazards have been studied. As regards natural risk, earthquake natural risk has been evaluated and for anthropogenic hazard an economic risk has been evaluated (air pollution) and two social risks have been analyzed (urban growth and urban vicinity in cultural heritage sites) Analyze the risk: for step B, different types of data have been collected. Indeed time series satellite images over Cyprus, geological and earthquakes data have been used in order to analyze the risks. Evaluate the risk: the final step involves the evaluation of all the risks regarding selected archaeological sites and monuments. Remote Sensing Procedure: In order to evaluate anthropogenic and natural hazards, archaeological sites of Cyprus (indicated in figure 2) and satellite images of different spatial and spectral resolution were used. The overall methodology applied at this study is shown below: Map all the archaeological sites using existing cadastral maps of Cyprus, scale 1: Quantify anthropogenic and natural hazards. For this purpose eight time series multispectral and panchromatic satellite images (e.g. CORONA, IKONOS, QuickBird) were used in order to examine: a) the urban expansion from the beginning of the 1960 until For this purpose a rectangle of 6 x 4 Km will be drawn around each archeological site in order to estimate the urban development in hectares for the last 50 years. Further to land use changes the minimum distance (urban vicinity) of urban development will be recorded, b) seismic hazards for the archaeological sites using peak ground acceleration values (PGA). These values will enable the authors to estimate the risk of the sites against an earthquake and c) air pollution hazard using satellite imagery and calculating aerosol optical thickness. The pre-processing and post-processing analysis of satellite data was made in ERDAS 10 Imagine and ArcGIS 9.3 software packages. Risk assessment analysis of the impact of the above mentioned natural and anthropogenic hazards. RESOURCES The satellite images applied in this study are tabulated as shown in table 1. Moreover their footprints are shown in figure 2. 3/11

4 Table 1: Satellite images No Satellite image Date Spatial resolution Wavelength 1 CORONA 1962/07/ m VIS 2 CORONA 1963/06/ m VIS 3 CORONA 1973/07/ m VIS 4 IKONOS 2000/03/14 0.8m RGB 5 QuickBird 2003/01/23 0.6m RGB 6 QuickBird 2004/07/ m NIR-R-G 7 Landsat ETM+ 2009/05/25 30 m NIR-R-G-B 8 Google Earth Recent < 30m RGB , 5 1, 2, 8 Figure 3: Footprints of the satellite images used in the study. The numbers indicated at the right of the images are taken for table 1. CORONA satellite images dated in 1962/07/21, 1963/06/27 and 1973/07/22 declassified in 2002 were used. It must be emphasized that this is the first time, where such kind of imagery is evaluated for monitoring archaeological and cultural sites in Cyprus. CORONA declassified satellite imagery have become a valuable tool to archaeologists due to its high spatial resolution and its low cost [9]. Two high resolution Quickbird and one true color IKONOS images dated in 2004/07/19, 2003/01/23 and 2000/03/14 respectively over the SW part of Cyprus were also used. Moreover, a recent multispectral Landsat ETM+ image (2009/05/25) was used. Satellite images such as Quickbird and IKONOS can provide high spatial resolution data over cultural sites. Although the high spatial resolution of these images (can be less than 1m) and therefore can be benefit the maximum to the archaeological research, the low temporal variation is a major prohibitive factor for using them [9]. 4/11

5 Geometric correction was applied for all the available images. An affine transformation was selected, since the sites are located in flat regions and therefore the distortion of the photographs due to the elevation is not significant. Post processing techniques such as Normalized Difference Vegetation Indices and supervised Classification for Landsat ETM+ image (2009/05/25) were applied in order to analyze the urban activity over the last 50 years in the archaeological sites. CHANGE DETECTION TECHNIQUES FOR EXTRACTING URBAN ACTIVITY FROM FOR ALL THE ARCHAEOLOGICAL SITES The urban activity on the south coastal areas of Cyprus, over the last 50 years was determined using the available aerial and image data (see table 1). Although the spatial resolution is different for each sensor and satellite image, an accuracy of ± 30 m can be assumed for all the images. The total area selected for extracting the urban activity was set as 6 x 4 Km, around each archaeological site. For Nea Paphos and Tombs of the Kings the data imagery goes back to Table 2: Urban activity as recorded through satellite imagery from Archaeological Site Area Urban activity Square Km *(1962 / 2010) **(2000 /2010) Vicinity of urban activity from the archaeological site Amathus * Kourion * Palaepaphos * Nea Paphos ** Tombs of the Kings ** Urban activity 0 / 4.9 Sea 1.5 other 22.5/ 17.6 Urban activity 1.0 / 2.4 Sea 0 other 23.0 /21.6 Urban activity 0.2 / 1.7 Sea 0.8 other 23.0/21.5 Urban activity 5.2/6.5 Sea 2.8 other 16.0/14.7 Urban activity 8.8/ 11.7 Sea 0.2 other 15.0/12.1 > 500 m 1963 / m 2009 / 2010 > 800 m 1962/1963/1973/2009/ m 1963/2004/2009/ m 2000/2003/2004/2009/ m 2000/2003/2004/2009/2010 5/11

6 No Archaeological Site Table 3: Urban results analysis for the period % difference of urban activity from * Vicinity of urban activity from the archaeological site in 1962 Vicinity of urban activity from the archaeological site in Amathus 490% Kourion 140% Palaepaphos 750% Nea Paphos (last 10 years) Tombs of the Kings (last 10 years) 25% % * % difference of urban activity from is calculated as: [(hectares of urban act hectares of urban act. 1962)/ hectares of urban act. 1962] * 100 As it is shown in tables 2 and 3, a significant increase of urban activity has been recorded in the south coastal areas of Cyprus. Using Landsat ETM+ image (2009/05/25) a supervised classification for Kourion and Nea Paphos archaeological sites was made. For the supervised classification, the Normalized Difference Vegetation Index (NDVI) was used, in order to assist the classification procedure. The results highlight the urban expansion as it was near these archaeological sites in 2009 (see figure 4). Previously analysis by Hadjimitsis et al. (2005) has shown the rapid activity over the area of Nea Paphos using satellite imagery from 1985 to 2000 [10]. Figure 4: Supervised Classification results (left) for Kourion (above) and Nea Paphos (down) archaeological sites and Landsat ETM+ image taken in 2009 (right) (red = urban; yellow=land; blue = water; green=irrigated/vegetated areas). Archaeological sites are indicated in a circle. 6/11

7 For Amathus archaeological site, the urban activity over the last 50 years is obvious (see figure 5). CORONA satellite images show clearly the growth of the urban activity around the site. The highway road passes only 100 m north to Amathus. For Kourion, although the minimum distance was not changed, a significant urban activity was recorded at the eastern and western part of the region. For Palaepaphos site, the case is quite different (see figure 5). All the east area of Kouklia village (Paleapaphos) is still unexploited, while at the west area the urban expansion has been increase dramatically. The minimum distance for the Nea Paphos archaeological site has remain the same for the last 10 years but a more dense urbanization is occur. The same phenomenon can be seen and at Tombs of the Kings archaeological site. Figure 5: Above: Amathus archaeological site in 1963 CORONA image (left) and 2010 Google (right). Down: Palaepaphos archaeological site 1963 CORONA image (left) and 2004 QuickBird image (right) SEISMIC HAZARD MAPS In order to evaluate the potential danger that the monuments are exposed to earthquakes, seismic hazard maps where used (data source: Cyprus Geological Survey). As it is shown in figure 6, the prone area of Cyprus is the coastal zone that extends from Paphos through Limassol and Larnaca to Famagusta (west to east coastal areas of Cyprus). All the archaeological sites mentioned in the specific work are located in these seismogenic areas of the island. The peak ground acceleration (PGA) values for Cyprus range from 0.16 s to 0.42g (1 g = 9.81 m s -2 ) (values by [11]). Values from 0.2g to 0.3g (approximate) are added when designing new buildings by civil engineers in Cyprus, 7/11

8 for safety reasons against earthquakes. Figure 6: Map showing the seismic hazard for Cyprus. PGA values for the island of Cyprus (%). Source: Cyprus Geological Survey Using GIS analysis all public sectors that are involved for protection of the archaeological sites can use seismic hazard maps in order to classify the monuments according their hazard. A most accurate analysis can be carried out fusing also other source of data such as geological formation, construction materials of the monuments, height of the monuments e.t.c. Table 4: PGA values for archaeological sites No Archaeological Site PGA values 1 Amathus Kourion Palaepaphos Nea Paphos Tombs of the Kings 0.37 AIR POLLUTION IMPACT ON ARCHAEOLOGICAL SITES In order to analyze air pollution impact to the archaeological sites of Cyprus, atmospheric path radiance (Lp) (and aerosol optical thickness, AOT) has been determined for the Landsat image acquired on 2009/05/25. Path radiance is an indicator of air pollution in the area. The determination of atmospheric path radiance (and AOT) has been done using the darkest pixel atmospheric correction method which has been found to be an effective method for the visible bands as shown by Hadjimitsis et al. (2004) [12]. Using the method described by Hadjimitsis (2009) [see 13] the image has been divided in grid cells as shown in figure 7 (10 x 10 Km) and the Lp for each grid has been calculated. Values of Lp<47 correspond to AOT=0.13 for non very hazy atmospheres, Lp =47-60 corresponds to moderate AOT = , while Lp > corresponds to AOT = These values are empirical values found from previous studies in which such method has been already applied [see 14]. 8/11

9 High : 79 Low : 59 Figure 7: Lp distribution above the archaeological sites as calculated from Landsat TM in 2009/05/25 RISK ASSESMENT ANALYSIS In order to estimate an overall risk of the archaeological sites due to the anthropogenic and natural a risk index for each factor (urban activity; minimum distance of urban activity in the vicinity of an archaeological site; seismic PGA and air pollution impact) was determined. All factor where considered to have an equal impact on the selected archaeological sites and monuments. It must be emphasized that only seismic PGA can have an instant impact at the archaeological sites. However, the impacts of urban activity, urban vicinity and air pollution parameters, on the archaeological monuments can be far less obvious, yet equally serious as the previous one. The risk index has been formulated by the authors such as for factor 0: for low risk; 1: for moderate risk and 2: for high risk. The impact of each factor has been determined according to this three part division as follows: Urban activity/ Vicinity of urban activity: The policy of Department of Antiquities and Department of Town Planning and Housing of Cyprus regarding the urban growth is limited to protect by law parcels around an archaeological site. This inevitably has caused serious problems to a holistic approach regarding urban activity near archaeological sites. For the aims of the study the following categories have been determined: Urban activity: low risk (factor =0) for less than 100% expansion over the last 50 years; moderate risk (factor =1) for 100%-300% expansion over the last 50 years and high risk (factor =2) for over than 300% expansion over the last 50 years; Vicinity of urban activity: low risk (factor =0) for over than 500m distance of urban activity near the archaeological sites over the last 50 years; moderate risk (factor =1) for a distance between m of urban activity near the archaeological sites over the last 50 years; and high risk (factor =2) for less than 200m distance of urban activity near the archaeological sites over the last 50 years Earthquake (PGA values): As it was found the peak ground acceleration (PGA) values for Cyprus range generally from 0.16 s to 0.42g (1 g = 9.81 m s -2 ) and values between 0.2g-0.3g are added when designing new infrastructures by civil engineers in Cyprus, for safety reasons against earthquakes. For the aims of the study the following categories have been determined: 9/11

10 PGA values: low risk (factor =0) for PGA values less than 0.2g; moderate risk (factor =1) for PGA values from than 0.2g 0.3g and high risk (factor =2) for PGA values over than 0.3g. Air pollution (Lp values): As it was found from the literature [14] values of Lp<47 correspond to AOT=0.13 for non very hazy atmospheres, Lp =47-60 corresponds to moderate AOT = , while Lp > corresponds to AOT = Therefore the authors have categorized the impact of the air pollution as follows: Lp values: low risk (factor =0) for Lp values less than 47; moderate risk (factor =1) for Lp values from than and high risk (factor =2) for Lp values over than 60. According to these values the risk assessment analysis as shown in table 5 was calculated: No Archaeological Site Table 5: Risk Assessment analysis Urban activity 0: <100% 1: % 2: >300% Vicinity of urban activity 0: > 500m 1: m 2: < 200 m Seismic PGA 0: : : >0.3 Air pollution impact 0: Lp < 47 1: 47<Lp<60 2: Lp >60 1 Amathus Kourion Palaepaphos Nea Paphos Tombs of the Kings Table 5, shows a quantified form the risk assessment analysis for five of the main archaeological sites of Cyprus against anthropogenic and natural hazards. Amathus and Palaepaphos case studies as can been seen, are the most affected archaeological site. CONCLUSIONS This paper aims to highlight the benefits of using remote sensing techniques and GIS analysis tools for monitoring archaeological sites of Cyprus. An integrated use of both satellite remote sensing techniques and GIS for monitoring anthropogenic and natural hazards using archived and up-to-dated multi-temporal remotely sensed images at areas nearby to cultural heritage sites and monuments in Cyprus has been found to be an ideal tool for monitoring purposes. Although the data used in this paper are limited for an accurate multivariable risk assessment analysis, the results explore the potential of using both GIS and remote sensing for applying risk assessment studies for archaeological sites in Cyprus. Urban activity has been found to play a basic role in this, since it has been dramatically increased in the surrounding area of the archaeological site for the last 50 years. One of the future tasks of this study is to explore more 'risk factors' in the analysis for further validation and assessment. 10/11

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