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GPR at Sant Adriano church

Thesis
by

Slobodan Miljatovic

on 4 January 2013

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Transcript of GPR at Sant Adriano church

History Ground penetrating radar (GPR) Work Objectives Results and discussion Conclusions and recommendations Acquisition Data processing The road The hill The cemetery Romans arrived in Brenna - Olgelasca in 196 ac. Brenna territory has soon been divided in centurie. Today there are not so many evidences of Roman presence. Division of the area in centurie. Cadastral map from 1722. Roman remains accidentaly found during excavation in 1960. Ancient Roman altar. Cadastral map from 1877. RADAR - radio detecting and ranging
Term is applied for all geophysical techniques employing radio waves 1 - 1000 MHz
The response we detect is due to the contrast of subsurface materials
Greater the amplitude, the greater is the contrast
As EM waves passes through the material it suffers attenuation Cone of transmission Precondition for object detection is that it re-emits portion of energy falling on it
Energy received creates an image of subsurface features
It is possible to determine depth, location and material of the anomaly
Some buried targets have well-known unique reflections GPR has gained enormous popularity in archeology
Non invasive method
Two most important parameters are resolution and depth, inversely related
We should be aware of soil type prior to investigation Identify the precise location of known archeological feature (road)
To explore the existance of the features not known and identify their precise locations (oratorio, cemetery and other) Thesis objectives
Detailed field survey and data collection
Data post processing using 2D and 3D modules of REFLEX
Examination and interpretation of the results Objectives to be reached by: The investigation was performed using Detector Duo GPR (Industria dei Sistemi)
Equipped with two antennas, frequencies 700MHz and 250Mhz
Allows simultaneous use of both antennas Instrumentation Preliminary survey Initially, random survey was necessary to define points of interest
Three areas have been chosen for detailed investigation The road The hill Cemetery Dimensions 10 x 7.5 m, line direction W-E
Line separation 0.5 m
Road suspected to be in close proximity to the church Dimensions 11.5 x 2 m, line direction N-S
Line separation 0.5 m
Strong anomalies detected at the entrance to the forest Dimensions 8 x 5 m, line direction N-S
Line separation 0.25 m
Various unknown anomalies detected Typical processing flow Data editing In this phase data were mainly corrected for starting and finishing point
Necessary for 3D interpretation
Can include other operations such as data file re-organization, data file merging, inclusion of elevation information Basic processing Basic processing should leave the data reasonably intact
It included mainly dewow, gaining the data, spatial and temporal filtering
In some cases gain function has been specified and applied to the data set and in the others energy decay has been used
Mainly bandpass filter has been applied
Both basic and advanced processing has been performed using REFLEX 2D module
After defining good processing steps, sequence processing has been applied to the whole data set Advanced processing Advanced processing requires certain experience and it is more subjective
As a result, processed data are different from raw data
It included mainly 2D filtering (background subtraction), velocity analysis using hyperbola fitting, migration and attribute analysis Data interpretation Data interpretation were performed using REFLEX 3D module
Data were displayed as a 3D cube, created from previously processed parallel lines
Time slices, x-slices and y-slices have been carefully examined
To processed data sets envelope has been applied for improving the visualization 2D processing Profiles were not similar as it was initially believed
In the left corner it is highlighted the part suspected to represent the road
From 2D interpretation no other useful information has been obtained 3D interpretation Time slices of the 3D interpretation of the dataset taken in consecutive order, from left to right, at: 9 ns (32.5 cm), 15 ns (52.5 cm), 18 ns (56 cm) and 20 ns (70 cm) From 3D interpretation it is hard to distinguish the exact position of the road
Possible location: between 0.3 m and 0.5 m depth, around 8th m in x-direction
A number of anomalies is also present between 1st and 5th meter 2D processing Profiles were similar, mainly roots were detected in the top 1 m
Between 1st and 2nd meter no anomalies have been detected
In the first meter in x-direction a strong unknown anomaly has been detected (marked red), on the depth of 2 meters
It belongs to metal object and it is wide at least 0.5 m 3D interpretation Y-slices of the 3D interpretation of the data set taken showing the anomaly 3D interpretation Time-slices of the 3D interpretation of the dataset taken in consecutive order, from left to right, at: 7 ns (0.35 m), 15 ns (0.60 m), 23 ns (0.92 m) and 62 ns (2.48 m) 2D processing 3D interpretation Time-slices of the 3D interpretation of the dataset, taken in consecutive order, from left to right, at: 16 ns (0.28 m), 16 ns (0.64 m) and 19 ns (0.76 m) 2D processing The processing flow of the cemetery dataset, showing in the consecutive order: original profile, dewowed profile, filtered profile, gain applied, background subtraction, filtered, start time moved, migrated profile and profile with envelope applied. 2D processing 2D processing showed great difference among individual profiles, showing different anomalies
Key aspect in detecting graves is a pattern
In 2D analysis is hard to detect it
In this case the pattern was not detected and 3D analysis was performed in order to provide more information In the image, with U is labeled unknown anomaly, which was probably due to a large stone
With P is marked the encountered pipe In general GPR investigation could be regarded as successful
In the case where there was lack of historical data it was hard to interpret the results
In many cases, responses similar to archeological features can be also produced by stones
Processing very subjective
No reliable way but excavation to verify the results Conclusions Being honest in giving explanations, using relative terms - especially in case of lack of historical data
Having good experience
Combining with other geophysical methods - especially in case where we have lack of historical data Recommendations Many thanks to....... Thank you for your attention!
Questions&remarks? GPR INVESTIGATION AT SAINT ADRIANO CHURCH, BRENNA (CO) POLITECNICO DI MILANO Student:
Slobodan Miljatovic Supervisor: prof. Giancarlo Bernasconi
Co-supervisor: prof. Valentina Socco Short outline Macrolocation Microlocation Roman invasion Centurie Evidences of Roman presence Evidences of Roman presence Evidences of Roman presence Evidences of Roman presence The church today GPR fundamentals GPR fundamentals GPR fundamentals GPR fundamentals History of Brenna
GPR fundamentals
Objectives
Practical work
Results and discussion
Conclusions and recommendations Prof. Giancarlo Bernasconi
Prof. Valentina Socco
Dino Ballabio and his family Oratorio
Tombs
Road
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