Modeling of Archaeomagnetic Anomaly Maps

112 Pages·2022·7.281 MB·English

by  Hazel Deniz Toktay

SpringerBriefs in Applied Sciences and Technology
Mathematical Methods
Hazel Deniz Toktay
Modeling of
Archaeomagnetic
Anomaly Maps
SpringerBriefs in Applied Sciences and Technology
Mathematical Methods
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Anna Marciniak-Czochra, Institute of Applied Mathematics, IWR, University of
Heidelberg, Heidelberg, Germany
Thomas Reichelt, Emmy-Noether Research Group, Universität Heidelberg,
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Hazel Deniz Toktay
Modeling
of Archaeomagnetic
Anomaly Maps
Hazel Deniz Toktay
Department of Geophysical Engineering
Istanbul University-Cerrahpasa
Istanbul, Turkey
ISSN 2191-530X ISSN 2191-5318 (electronic)
SpringerBriefs in Applied Sciences and Technology
ISSN 2365-0826 ISSN 2365-0834 (electronic)
SpringerBriefs in Mathematical Methods
ISBN 978-981-19-4218-1 ISBN 978-981-19-4219-8 (eBook)
https://doi.org/10.1007/978-981-19-4219-8
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Introduction
Archaeological excavations are highly expensive works that require a lot of time
and labour. Before the excavation, knowing the subsurface structures in the area
to be excavated is of great importance. Therefore, it is necessary to make scans in
these areas with auxiliary application techniques, which cannot be done with clas-
sical archaeological methods [16]. Investigation of archaeological sites that do not
damage potential structures (non-destructive) is often called archaeological prospec-
tion. Geophysical methods are one of the most preferred applications in archaeolog-
ical prospection. Applications of these methods in archaeological research are called
“Archaeological Geophysics” [22] or “archaeogeophysics” [4]. By using geophys-
ical methods, the image of subsurface objects can be found non-destructively without
excavation. These are the magnetic, electromagnetic, electrical resistivity, gravity
and ground-penetrating radar methods. When determining which method to use,
the subsurface structure and the applied method should be correctly associated.
The geophysical method chosen varies depending on the physical properties of the
structure in question.
Geophysical applications have been used throughout the world in archaeology
since the 1940s [16], providing great savings of time and money, especially in
mapping large areas. Archaeogeophysics deals with structures from a few centime-
tres to several metres in depth and size. These structures are generally “prehistoric”
foundations consisting of storage pits, house foundations, walls, stoves, furnaces and
other burnt objects, or “historical” foundations such as those of castle walls, theatres,
stadiums, temples and other large buildings, streets and house remains [28]. At the
beginning of the archaeological studies, the archaeogeophysical studies applied at the
site selection and excavation plan can determine the geometry and depth of the struc-
tures buried beneath the surface. In this way, time loss in excavations is prevented,
and excavation costs are significantly reduced.
Since the magnetic method can be completed quickly and is non-destructive,
it has been one of the most preferred archaeological surveys [66]. It is generally
used in detailed geophysical surveys or in excavation studies to locate target areas.
The method can be applied to a wide range of targets located in regions with various
vii
viii Introduction
geological characteristics. The results obtained from minor variations in the magnetic
field can determine signs of the past periods [3, 10, 30, 34,44].
In the magnetic method, properties of subsurface structures with different
magnetic susceptibilities are utilized. In an environment with low magnetic suscep-
tibility, units with high magnetic susceptibility can be detected. Magnetization in
archaeological sites may result from several reasons: the thermal remanent magneti-
zation of bricks, tile heaps and ancient fire pits, building foundations with magnetic
rock components, storage areas and natural environments with iron oxides including
ferrous metals [28].
Numerical approximations of the depth and physical properties of buried struc-
tures can be made with the help of magnetic data collected using modern and sensitive
instruments. The magnetic method is a natural field method. Therefore, the measured
magnetic field values are due to the magnetic contrasts of the subsurface source distri-
butions and are obtained superposed. Magnetic data sets are converted into 2D maps.
The anomalies on the maps are indicative of the subsurface source distributions. An
attempt to interpret the physical and geometric features of the archaeological struc-
tures is made by associating these anomalies with the subsurface geological sources.
Although this method is easy to apply, some remanent magnetization and noise
factors should be considered during the interpretation phase. These factors should
be taken into account when producing 3D models, and data sets should be analysed
using several techniques.
In this book, we consider highlighting the potential subsurface structure, which
can make significant contributions to the planning of the archaeological excavation
process. By studying non-destructive geophysical methods, we aim to discover the
hidden cultural heritage of Oluz Mound.
This book consists of five chapters. In Chap. 1, for the convenience of the readers,
we will recall some basic facts. In Sect. 1.1, the concepts that are frequently used
in magnetic prospecting applications are briefly explained. Section 1.2 describes the
vectorial properties of the geomagnetic field. Finally, Sect. 1.3 is a brief informa-
tive description of the horizontal and vertical components of the frequently used
geological models, which are helpful in the definition and interpretation of random
geological sources.
Chapter 2 is of an introductory character and consists of four sections. Section 2.1
contains location information and geological features of the survey area from which
the map created with the archaeomagnetic data is obtained. Section 2.2 describes
previous archaeological studies on the survey area. In Sect. 2.3, we will present the
historical background of the edge detection and depth calculation methods applied
to the magnetic data sets. In Sect. 2.4, a synthetic model is created with initial param-
eters similar to archaeological building units found on shallow surfaces. Theoretical
anomalies of the created model have been calculated and are shown in Sect. 2.4.1.
Chapter 3 considers the determination of inclination and declination angles from
the total magnetic anomaly maps on archaeological sites. It is necessary to know the
magnetic inclination and declination angles of the study area to accurately locate
the buried structures on the total magnetic anomaly maps. Section 3.1 deals with
the calculation of inclination and declination angles using the Dannemiller and Li
Introduction ix
method. Section 3.2 is devoted to analysing the inclination and declination angles
of the model created in Sect. 2.4. Moreover, we made a numerical simulation that
confirms obtained theoretical results. In Sect. 3.3, we determine the inclination and
declination angles belonging to the real archaeomagnetic field data.
In Chap. 4, we deal with modeling to eliminate the problem of uncertainty
regarding the location of buried archaeological structures. This chapter consists of
five sections. In Sect. 4.1, data enhancement techniques are examined. Sections 4.1.1
and 4.1.2 include brief explanations of the upward continuation and reduction to pole
methods. In Sect. 4.2, the tilt angle and automatic gain control methods are explained
from the viewpoint of edge detection. In Sect. 4.3, we apply methods on the synthetic
model and verify that the obtained results confirm the initial values. In Sect. 4.4,we
determine that the horizontal boundaries belong to the actual archaeomagnetic field
data.
Chapter 5 studies the depth values of potential buried structures that cause anoma-
lies from the total magnetic anomaly maps of an archaeological excavation area. To
this end, in Sects. 5.1.1–5.1.3, derivative-based methods such as tilt angle depth,
source parameter imaging and improved source parameter imaging are examined.
Section 5.2 is devoted to depth calculations using the synthetic model. By applying
these three methods, the depth values of the model blocks are calculated, and the
values obtained according to each method are compared and analysed. In Sect. 5.3,
the depth values of potential archaeologic remanents from the real archaeomagnetic
field data have been calculated.
Chapters 3–5 are based on the results obtained in my Ph.D., which was done at
the Istanbul University under the supervision of Davut Aydog˘an and Fethi Ahmet
Yüksel. I am immensely thankful to them for inspiring discussion in leading this
Ph.D., their patience and support and sharing their knowledge. I would like to express
my eternal gratitude to Messoud Efendiev for encouraging me to write this book
and his unique guidance. I am extremely grateful to Springer for the opportunity
to publish this book. I would like to thank Masayuki Nakamura, Bhagyalakkshme
Sreenivasan, Revathy Manikandan and the Springer team for helping me throughout
the production process. I also would like to express my gratitude to the reviewers for
their time and constructive comments that increased the quality of this book.
Last but not least, I would like to thank my parents and my husband for their
patience, trust and support during the preparation of this book.
Hazel Deniz Toktay
Contents
1 Auxiliary Materials ............................................. 1
1.1 Basic Concepts in Magnetics ................................. 1
1.2 Components of the Geomagnetic Field ........................ 3
1.3 Magnetic Anomalies of Model Sources ........................ 5
2 Historical Background .......................................... 9
2.1 Survey Area ............................................... 9
2.1.1 Geological Structure of the Study Area .................. 11
2.1.2 Stratigraphic Structure of the Study Area ................ 13
2.1.3 Active Fault Lines of the Region ....................... 15
2.2 Previous Archaeological Studies on the Amasya Oluz Mound
Site ....................................................... 15
2.3 Magnetic Data Sets ......................................... 18
2.4 Synthetic Model ............................................ 21
2.4.1 Theoretical Anomalies ................................ 22
3 Detection of Inclination and Declination Angles from Total
Magnetic Anomaly Maps on Archaeological Sites ................. 25
3.1 Dannemiller and Li Method .................................. 26
3.2 Synthetic Model Applications ................................ 28
3.3 Field Applications .......................................... 29
3.4 Conclusions ............................................... 30
4 Quantitative Analysis of Total Magnetic Anomaly Maps
on Archaeological Sites—Edge Detection ......................... 33
4.1 Data Enhancements ......................................... 34
4.1.1 Upward Continuation Method ......................... 34
4.1.2 Reduction to Pole Method ............................. 37
4.2 Detection of Horizontal Boundaries ........................... 39
4.2.1 Tilt Angle Method ................................... 39
4.2.2 Automatic Gain Control (AGC) Method ................. 40
4.3 Synthetic Model Applications ................................ 41
xi