Nikos Papadopoulos

Geophysical investigations at the Istron archaeological site, eastern Crete, Greece using seismic refraction and electrical resistivity tomography

The subsurface characteristics of the archaeological site of Priniatikos Pyrgos at Istron, Eastern Crete were studied through the combined use of seismic and electrical tomography techniques. Twenty-nine seismic refraction profiles were applied to determine soil thickness and bedrock geometrical characteristics. First arrivals were picked and a 3D algorithm of seismic tomography was used to invert the travel times. To confirm the reliability of the final results a checkboard test was used. Part of the seismic area was overlapped with six electrical resistivity tomography sections. The ERT data were used to validate the resulted tomographic images. The integrated application of these tomographic methods enhanced the knowledge regarding the geological conditions and contributed in the archaeo-environmental reconstruction of Istron area by providing indications regarding the ancient harbour of the nearby settlement.

Geo-Characterization at selected accelerometric stations in Crete (Greece) and comparison of earthquake data recordings with EC8 elastic spectra

To estimate the seismic response according to Eurocode (EC8) and almost all other national codes, site conditions have to be properly characterized so that soil amplification and the corresponding peak ground motion can be calculated.In this work, different geophysical and geotechnical methods are combined in order to define the detailed ground conditions in selected sites of the Hellenic Accelerometric Network (HAN) in Crete. For this purpose, the geological information of the sites and shear wave velocity, calculated from surface wave measurements, is used. Additionally, ground acceleration data recorded through HAN have been utilized from intermediate depth earthquakes in the broader area of South Aegean Sea.Using the recorded ground motion data and the procedure defined in EC8, the corresponding elastic response spectrum is calculated for the selected sites. The resulting information is compared to the values defined in the corresponding EC8 spectrum for the seismic zone that includes the island of Crete.The comparison shows that accurate definition of ground type through geological, geotechnical and geophysical investigations is important. However, our current comparison focuses on the distribution of values rather than the absolute values of EC8-prescribed spectra, and the results should be considered in this context.

Integrated use of satellite remote sensing, GIS, and ground spectroscopy techniques for monitoring olive oil mill waste disposal areas on the island of Crete, Greece

ABSTRACT Olive oil mill wastes (OOMW) constitute a major pollution factor in olive-growing regions and an important problem to be solved for the agricultural industry. Olive oil mill wastes are normally deposited in tanks, or directly into the soil or even on adjacent torrents, rivers, and lakes, posing a high risk of environmental pollution in regard to public health. This study aims to develop integrated satellite remote sensing, geographical information systems (GIS), and ground spectroscopy methodologies to detect and monitor OOMW disposal areas on the island of Crete, Greece in the Southeastern Mediterranean. More than 1000 disposal tanks were mapped through an extended global positioning system (GPS) survey that took place throughout the island. Satellite images of both high (IKONOS) and medium (Landsat 8 OLI (Operational Land Imager)) resolution were preprocessed and analysed by applying geometric, radiometric, and atmospheric corrections. A library with a spectral signature of OOMW including both different time periods and satellite sensors was developed. At the same time, ground spectroscopy campaigns were carried out and a complementary spectral signature library was developed. The narrow band reflectance of ground measurements was recalculated using the relative response filters of the corresponding satellite sensors. Both libraries were compared for their accuracy through statistical approaches and the optimum spectral range for detecting OOMW areas was estimated. Subsequently, further auxiliary image-processing techniques such as image fusion, linear spectral unmixing (LSU), false-colour composites (FCCs), image classification, and principal component analysis (PCA) were applied to satellite images to enhance OOMW patterns, and an innovative OOMW detection index for Landsat 8 was developed. In addition, several vegetation indices were applied and compared in regard to their efficiency in detecting waste ponds. Finally an integrated, semi-automatic methodology was developed in the GIS environment employing classification algorithms for the detection of waste ponds. This study highlights the potential of satellite remote sensing, GIS, and ground spectroscopy in the semi–automatic detection of OOMW disposal areas in the context of the Mediterranean landscape.

Extraction of Archaeological Information Using High Resolution FormoSAT-2 Data

This paper investigates the potential use of the high resolution FormoSAT-2 sensor for supporting archaeological research. Although satellite remote sensing data have been widely used in the context of archaeological research, the high-resolution FormoSAT-2 dataset has attracted little attention. For a better understanding of the Neolithic habitation of the Thessalian plain in central Greece, the authors have used a variety of remote sensing techniques, including satellite and in situ data. In situ spectroradiometric measurements have been recalculated based on the Relative Response Filters of the FormoSAT-2 sensor and compared with other medium- and high-resolution sensors. The FormoSAT-2 spectral characteristics tend to give similar results with the Landsat 5 TM and 7 ETM+ sensors during the whole phenological cycle of the crops, which make this ideal for pan-sharpening fusion techniques. As we found, FormoSAT-2 data can be sufficiently used for the documentation of tells (locally called magoules) in th...

Geodiametris: an integrated geoinformatic approach for monitoring land pollution from the disposal of olive oil mill wastes

The olive-oil industry is one of the most important sectors of agricultural production in Greece, which is the third in olive-oil production country worldwide. Olive oil mill wastes (OOMW) constitute a major factor in pollution in olivegrowing regions and an important problem to be solved for the agricultural industry. The olive-oil mill wastes are normally deposited at tanks, or directly in the soil or even on adjacent torrents, rivers and lakes posing a high risk to the environmental pollution and the community health. GEODIAMETRIS project aspires to develop integrated geoinformatic methodologies for performing monitoring of land pollution from the disposal of OOMW in the island of Crete -Greece. These methodologies integrate GPS surveys, satellite remote sensing and risk assessment analysis in GIS environment, application of in situ and laboratory geophysical methodologies as well as soil and water physicochemical analysis. Concerning project’s preliminary results, all the operating OOMW areas located in Crete have been already registered through extensive GPS field campaigns. Their spatial and attribute information has been stored in an integrated GIS database and an overall OOMW spectral signature database has been constructed through the analysis of multi-temporal Landsat-8 OLI satellite images. In addition, a specific OOMW area located in Alikianos village (Chania–Crete) has been selected as one of the main case study areas. Various geophysical methodologies, such as Electrical Resistivity Tomography, Induced Polarization, multifrequency electromagnetic, Self Potential measurements and Ground Penetrating Radar have been already implemented. Soil as well as liquid samples have been collected for performing physico-chemical analysis. The preliminary results have already contributed to the gradual development of an integrated environmental monitoring tool for studying and understanding environmental degradation from the disposal of OOMW.

Different Processing and Inversion Methods for Resolving Vs Profiles in Engineering Geophysics Using Surface Wave Data

Recent advances in Seismic Codes increased the necessity in Engineering Geophysics to use surface wave analysis as a tool. The shear wave velocity profile had to be resolved to calculate the site amplification in case of an earthquake event, necessary also for seismic hazard studies. In our approach we present the results from Surface Wave data acquired in different site in Crete Island (Greece) at strong motion sites. Passive and Active data at linear and circular geometries have been analyzed and the corresponding processing and inversion results are compared. Although one would comment that there are discrepancies on Dispersion Curve results the resulted ground profiles up to a shallow depth show considerable agreement. However, this is site dependent and in order to increase the accuracy and reliability of results one should be careful with the assignment of different modes in surface wave analysis and also combine the results provided.

3D Mapping of the Submerged Crowie Barge Using Electrical Resistivity Tomography

This study explores the applicability and effectiveness of electrical resistivity tomography (ERT) as a tool for the high-resolution mapping of submerged and buried shipwrecks in 3D. This approach was trialled through modelling and field studies of Crowie, a paddle steamer barge which sunk at anchor in the Murray River at Morgan, South Australia, in the late 1950s. The mainly metallic structure of the ship is easily recognisable in the ERT data and was mapped in 3D both subaqueously and beneath the sediment-water interface. The innovative and successful use of ERT in this case study demonstrates that 3D ERT can be used for the detailed mapping of submerged cultural material. It will be particularly useful where other geophysical and diver based mapping techniques may be inappropriate due to shallow water depths, poor visibility, or other constraints.

A Regional Approach to Ancient Urban Studies in Greece Through Multi-Settlement Geophysical Survey

ABSTRACT The systematic exploration of large archaeological sites in the Mediterranean has evolved considerably since the “big dig” excavations. Pedestrian field surveying and remote sensing applications, including satellite and airborne image analysis, are now practical and relatively cost-efficient methods of characterizing large and diachronically diverse landscapes on regional scales. However, the use of geophysical techniques as a means for exploring manifold archaeological contexts is still in its infancy. In this paper, we highlight the advantages of archaeological geophysics to conduct regional surveys in the Mediterranean. Through a multi-site geophysical fieldwork campaign to investigate the patterns and dynamics of ancient cities in Greece, we show how geophysics offer new opportunities for characterizing the spatial attributes and regional dynamics of urban landscapes, and, in doing so, we make an argument for its wider adoption on regional survey projects.

Revealing the urban features of the ancient greek city of Mantineia through the employment of ground penetrating radar

An extensive geophysical survey at the ancient Greek settlement of Mantineia in Peloponnese identified near surface features of archaeological interest that provide valuable information about the internal organization of the city. A multi-method approach was adopted for the application of various geophysical methods, spanning from magnetics to electromagnetics, soil resistance and GPR techniques, coupled with aerial and satellite remote sensing. The resolution of the GPR approach was crucial in identifying the details of the urban space and its development over time. The supremacy of the GPR in revealing the lateral expansion of the architectural residues and their vertical extent was obvious with respect to the rest of the methods applied.

Cross validation of geotechnical and geophysical site characterization methods: near surface data from selected accelerometric stations in Crete (Greece)

The specification of the near surface ground conditions is highly important for the design of civil constructions. These conditions determine primarily the ability of the foundation formations to bear loads, the stress – strain relations and the corresponding settlements, as well as the soil amplification and corresponding peak ground motion in case of dynamic loading. The static and dynamic geotechnical parameters as well as the ground-type/soil-category can be determined by combining geotechnical and geophysical methods, such as engineering geological surface mapping, geotechnical drilling, in situ and laboratory testing and geophysical investigations. The above mentioned methods were combined, through the Thalis ″Geo-Characterization″ project, for the site characterization in selected sites of the Hellenic Accelerometric Network (HAN) in the area of Crete Island. The combination of the geotechnical and geophysical methods in thirteen (13) sites provided sufficient information about their limitations, setting up the minimum tests requirements in relation to the type of the geological formations. The reduced accuracy of the surface mapping in urban sites, the uncertainties introduced by the geophysical survey in sites with complex geology and the 1D data provided by the geotechnical drills are some of the causes affecting the right order and the quantity of the necessary investigation methods. Through this study the gradual improvement on the accuracy of site characterization data is going to be presented by providing characteristic examples from a total number of thirteen sites. Selected examples present sufficiently the ability, the limitations and the right order of the investigation methods.