Alexandre Novo

3D GPR in forensics: Finding a clandestine grave in a mountainous environment

In the present work we show a forensic case study carried out in a mountainous environment. Main objective was to locate a clandestine grave which is around 10-20 years old and contains human remains of one individual and a metallic tool, probably a pick. Survey design started with an experimental burial of a pick at the expected depth (1m) as well as the calculation of synthetic radargrams in order to know if the 250MHz antenna was suitable for its detection and to have a record of the reflection of the pick. Conclusions extracted from the experiments together with rough terrain conditions suggested the use of the 250MHz antenna which allowed a good compromise between target detection and dense grid acquisition of an extensive survey area.

Combining GeoEye-1 Satellite Remote Sensing, UAV Aerial Imaging, and Geophysical Surveys in Anomaly Detection Applied to Archaeology

This paper describes a method of combined ultra-high resolution satellite imaging, unmanned aerial vehicle (UAV) photography, and sub-surface geophysical investigation for anomaly detection, which was employed in a non-invasive survey of three archaeological sites in Northern Mongolia. The surveyed sites were a Bronze Age burial mound, a Turkish period tomb, and a steppe city fortification of unknown origin. For the satellite survey, 50 cm resolution pan-sharpened imagery was generated through a combination of multispectral and panchromatic data, collected from the GeoEye-1 earth-sensing satellite. The imagery was then used to identify the location of the aforementioned sites in an approximate area of 3000 km2 . Aerial photographs of the sites were obtained with two customized electric-powered UAVs: a fixed flying wing rear-propulsion plane and a multi-propeller “oktokopter” helicopter system. Finally, geophysical investigation was conducted with a GSM-19 Overhouser gradiometer, an EM38 electromagnetometer, and an IDS Detector Duo ground penetrating radar. The satellite imagery and aerial photographs were combined with the geophysical survey results and on-site surface observations to provide insight and contextual information about anomalies in multiple layers of data. The results highlight the effectiveness and robustness of the employed method for archaeological investigation in large, rugged and scarcely populated areas.

ADVANCES IN GPR IMAGING WITH MULTI-CHANNEL RADAR SYSTEMS FROM ENGINEERING TO ARCHAEOLOGY

Advances in ground penetrating radar imaging with multi-channel systems have greatly improved the speed and areal coverage of the ground. Along with improved imaging software, datasets recorded with multi-channel systems can be processed at similar speeds to coarsely spaced single channel data that would normally require additional time for interpolation processes to fill in the gaps between lines. With the cross-line spacing approaching a 1/4 wavelength of the transmitted microwaves into the ground, multi-channel systems have the advantage of complete coverage of a site with no need for interpolation in most cases except to fill in the gaps between adjacent tracks if so desired. Multi-channel systems do require additional RSP (radagram signal processes) in order to balance the channels and to condition the data prior to imaging. Spectral whitening and several other RSP methods are shown with their application to imaging of sites from bridge decks for deterioration to the discovery of subsurface archaeological remains. Data processed from several different multi-channel GPR systems are shown.

Masonry arch bridges evaluation by means of GPR

Some masonry arch bridges in Galicia (NW Spain) were surveyed with GPR using 250 and 500 MHz antennas. The main goal of this work was to perform an analysis of historical bridges, obtaining information about filling material homogeneity, detecting inclusions of different materials, defining structural faults -such as internal voids or cracks- and detecting ancient features -as hidden arches or previous profiles of the bridge-. Geometric 3D models of the surveyed bridges obtained with Laser Scanning methods, were used as inputs to create synthetic radargrams through FDTD simulations in order to help GPR data interpretation.

Checking the Signal Stability in GPR Systems and Antennas

The different components of GPR equipment have particular characteristics that, when taken together as a whole, give the system the stability required for correct usage. Besides the information provided by manufacturers about parameters affecting the stability of GPR equipments, their evolution with use and ageing suggest that each GPR system employed in detailed qualitative studies should be subject to routine analysis. This type of analysis is especially important in novel systems and antennas to understand their real capabilities and limitations. In this work, several tests are carried out in order to evaluate the stability of a GPR system working with three different antennas with nominal frequencies of 500, 800, and 1000 MHz. Some tests published by other authors, together with other tests proposed here, are adapted to be the starting point to develop a methodology for calibrating GPR devices and to verify proper operation.

Vertical and Horizontal Resolution of GPR bow-tie antennas

Since the characteristics of the detected reflections depend on the issued signal properties, a key factor for carrying out a successful GPR survey is to know as much as possible about the transmission features of the antennas. This information is essential when deciding the antenna and which is the most appropriate parameter configuration setting for a specific study. These characteristics vary for the different available GPR equipments. Numerous experimental tests have been developed in this way. In this paper we present the first results of set of experiments about the resolution capabilities of two commercially bow-tie antennas (1GHz and 800 MHz). The propagation media was air in this first study and the experimental results are compared with the theoretical estimations. The obtained conclusions are the first step in order to establish the real bounds for the detection capability of these antennas.

A GPR ARRAY SYSTEM FOR FAST ARCHAEOLOGICAL MAPPING: STREAM X AT AQUINUM ROMAN SITE (CASTROCIELO, ITALY)

To enhance the knowledge on the location of the unknown buried structures below levels currently studied through excavation at Ancient Aquinum (Castrocielo-Frosinone, Central Italy), an integrated archaeological and ground remote sensing study was initiated in 2008-2009 between University of Lecce and Institute for Technologies Applied to Cultural Heritage (ITABC, CNR) and it is still in progress today. To verify the preliminary interpretations and to enhance the subsurface knowledge in the centre of the urban area of Aquinum, an extensive geophysical survey, employing Ground Penetrating Radar (GPR) with both single-channel equipment and multi-channel GPR systems, was expedited in June 2011. The remote sensing results indicate good correlation between the interpretation of aerial photographs and GPR images at different depths, in addition to the discovery new unexpected buried buildings. The survey were made with single-channel (GSSI SIR3000 with 500 MHz antenna) and multichannel equipment using the new IDS STREAM X System for large-scale acquisition. The area of interest borders the first excavated portion of ancient public bath (thermae). In the present work a comparison between the data sets collected with the two different systems on the same area are analyzed and discussed. The archaeological excavations made (by Prof. Giuseppe Ceraudo – University of Salento, Lecce) during the summer 2011, have confirmed the structures detected with the geophysical methods.

From Pseudo-3D to full-resolution GPR imaging in archaeology: A complex Roman site in Lugo, Spain

This case study demonstrates how extra effort on data acquisition can beneficiate advanced interpretation of 3D GPR data over a complex Roman site situated in a semi-urban area. Two 250 MHz surveys during May 2007 and July 2008 were accomplished after Roman wall remains had been found by chance during soil remove works at Agro da Ponte (Lugo, NW Spain). First campaign covered the whole area by using a pseudo-3D strategy which was only enough for defining the areas of interest and some archaeological features. According to those results, next campaign was focused on a smaller area and based on an ultra-dense grid strategy which eventually revealed full-resolution images of walls, apses and chambers of a Roman villa.