SGS Berlin & Potsdam - University of Indonesia Geophysical Society Joint Field Camp 2012
The cooperation of the SEG student chapters of University of Indonesia Geophysical Society (UIGS) and Student Geoscientific Society Berlin & Potsdam (SGS) originated in the participation of the two project leads in the SEG Annual Meeting 2011 in San Antonio. The outcome of this event was a successful application for a grant of the SEG Foundation Field Camp program to conduct the SGS Berlin & Potsdam and UIGS Joint Field Camp 2012 on Java, Indonesia. This field camp involved a group of 14 Indonesian and 5 German students with various geoscientific backgrounds and levels of expertise. Additional partnerships with the Indonesian National Research and Development Center of Archeology, a local geophysics instrument company, the University of Indonesia and Freie Universitaet Berlin provided equipment, profound knowledge, training and financial support to help realizing this Indonesian-German Joint Field Camp 2012.
The objective of the Field Camp was to support the reappraisal of an important part of Indonesian history by mapping an archaeogeophysical target in Banten on Java. The targets of the survey were the buried palace foundations and fortress walls of the former Sultanate of Banten, which have been built between 1550 and 1596. The significance of the province of Banten can be traced through folklore, ancient manuscripts as well as religious and cultural material. At the same time, its archaeological targets are indicators of social and political patterns during time. By conducting geomagnetics, geoelectrics and ground-penetrating radar measurements the Field Camp participants wanted to help finding these subsurface structures, which would make archaeologists able to better understand the architectural design of the past. The geophysical assistance is of great benefit for archaeology, as proper excavation places can be precisely pinpointed, saving time and efforts in the later excavation activities. Besides, knowing where to search for subsurface artifacts helps to prevent damage during excavations. So far, the local Indonesian archaeologists had already explored and uncovered about 30 % of the Surosowan Palace, most of it build with bricks. Thus, it was the participants’ task to map other parts and to enable archaeologists to further uncover the subsurface structures according to the survey results. In addition to the advantages for the archaeologists and the population on Java, the project was a great opportunity for the participating students to gain valuable field work experience.
The archaeological site of Banten is located in westernmost Java, Indonesia. Morphologically, Banten is situated at the coast near the sea of Java at its north bordering alluvial landforms. The regional geology as well as the one of Java is characterized as recent, since it comprises the current geologic era Cenozoic, which contains the latest periods of Neogene and Quarternary. It consists of alluvial deposits. Therefore, the main components of the survey site subsoil are clay and sand. In 1550 Sultan Hasanuddin established the Sultanate of Banten and built the Surosowan Palace. In these times the region became an important trading center. Between 1570 and 1596 the Sultanate of Banten has been enlarged to the back country and a zig-zag asymmetric fortress wall surrounding the territory was built. The measures of the outer wall was 2 – 5 m height and about 2 m width. According to ancient maps it can be assumed that the fortress wall existed at least 100 years. In 1680 Dutch conquerors built a watch tower, the Speelwijk, which is still located right at the northwestern edge of the city. The annihilation and destruction of the Surosowan Palace began about 1815 resulting in burning down the palace by the conquerors. For the geophysical survey and the three applications eight grids have been defined, which were split into the two main survey areas of the Field Camp: The Surosowan Palace in almost the center of Banten and the Speelwijk, about 800 m away. The area of the Surosowan Palace presented many exposed architectural structures, while other parts were characterized by empty areas covered with soil and grass. Spots like elevations or long alignments of striking grass color were sought, since they foreshadowed where architectural structures might be expected beneath the earth. The measurements around Speelwijk were conducted to locate the former city wall.
Geological map of Java, Indonesia and the location of the Field Camp 
The applied measurements methods are typical for archaeological prospections. In order to be well versed the students who were not used to the relevant techniques were trained in advance with the necessary theory and practiced during a training field camp.
Geomagnetics - The target of the geomagnetics group was to measure the magnetic properties of different archaeological locations to find geomagnetic anomalies suspecting buried structures beneath the surface. In contrast to geoelectrics and georadar the geomagnetics survey should give a first impression of the subsurface. In order it was supposed to provide information for more detailed surveys of the other applications. The idea was to use a mobile proton precession magnetometer (PPM) in conjunction with a base station to measure the minute differences in the total magnetic earth field which can be caused by the variation of iron concentration in the soil, the difference in the magnetic susceptibility of disturbed soil and, even more important concerning this archaeological survey, the thermo-remnant magnetism of fired clay. The geomagnetics group consisted of six people taking care of the acquisition and processing of the data. The mobile PPM device was a quantum magnetometer data logger, whereas the base station was a geometrics g-856 magnetometer. In total data were acquired in seven different areas, which were characterized by different sizes and resolutions. The entire area covered by the geomagnetics survey was about 2200 sqm.
Geoelectrics - Geoelectrics (or also electrical resistivity tomography) is one of the key methods used for mapping archaeological sites. For the measurements direct current is induced into the underground by electrodes and an electrical field is created, depending on the allocation of specific electrical resistivity in the subsurface. By detecting differences in the electrical resistivity of underground structures the composition of the subsurface can be identified. Those resistivity anomalies are caused by different structures and material properties, e.g. walls foundations, basements or air-filled spaces. Using a suitable small electrode spacing, vertical as well as horizontal resolution are acceptable and even small structures can be detected. Due to the shallow depth which was most interesting in this archaeo-geophysical research, the applied electrode spacing was either 0.5 m or 1 m. The problem of very low resistivities, caused of a river directly next to some profiles could be solved when processing the datasets afterwards. For processing 2D- and 3D-models the program Res2DInv and DC3DInvRes (open source) has been used. The geoelectrics measurements were carried out on seven different grids and the geoelectrics group were of six people.
Ground-penetrating radar - As geoelectrics and geomagnetics ground-penetrating radar (GPR) has the advantage that underground structures can be investigated without being exposed, since the method provides a high resolution of the near-surface. The principle is to send by an antenna electromagnetic waves into the underground. The wave frequency might range from 10 – 10000 MHz. Depending on buried material or layer transitions the propagating waves are reflected and send back to the GPR device, where they are recorded by a receiver. After calculating the arrival time of the reflected waves and creating a velocity model, size and depth of the underground reflectors could be determined. GPR measurements have been implemented with a 200 MHz antenna on three grids and the grid spacing was 0.5 m. Unfortunately, data which were acquired in the Speelwijk area turned out as useless, since the soil was too wet. In general, GPR shouldn’t be applied in areas with a resistivity < 100 Ohm m. The GPR team was of six persons.
Summarized, it can be stated that in seven different areas architectural structures were detected. Moreover, it can be assumed that these structures correspond with high probability to the searched targets, i.e. the former city wall around Speelwijk area and housing structures in the Surosowan Palace. The sketch sums up all the data acquired and interpretation made in case of the former city fortress around Speelwijk Watch Tower. It illustrates the possible orientation of the wall, including a zigzag behavior, which of course needed to be treated with caution. Further measurements would be necessary to be able to map the whole wall in a greater area. Due to the shallow depth of the detected structures, excavations should be a good way to figure out whether these structures are real or not and for the first case whether they correspond to the former city wall or not. The data acquired in Surosowan Palace were quite promising too. Some structures could be resolved in good resolution with the ability to deliver an insight into former architectural walls. These results provided useful information for following excavations in this area. The survey groups had to cope with several challenging circumstances: Incomplete equipment made it often necessary to improvise, which devoured crucial survey time and also other complications, such as anthropogenic noise, dense vegetation or the topographical environment represented obstacles. But thanks to the efforts and creativity of engaged students these problems could be overcome. The entire project can be regarded as a success which brought young people from different cultures together and made them cooperate on a high scientific level. Moreover, project participant Robert Roskoden presented the survey results on the 4th International Geosciences Student Conference 2013 in Berlin, Germany.
- Böhnke, C., Fussek, F., Guerreros, J. G., Roskoden, R., Steckenreuther, P. (2012): SGS Berlin & Potsdam and UIGS Joint Field Camp 2012. An Indonesian-German archaeogeophysical project in Banten Lama on Java, Indonesia.
- University of Bucharest SEG Student Chapter - SGS Berlin & Potsdam Joint Field Camp 2008
- SGS Berlin & Potsdam - University of Bucharest SEG Student Chapter Joint Field Camp 2009
- SGS Berlin & Potsdam High School Field Camp 2011
- Institute of Applied Physics Nizhny Novgorod - SGS Berlin & Potsdam Joint Field Camp 2014
Personal experience written by a Field Camp participant