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Change Over Time

An InternAtIonAl JournAl of conservAtIon And

the buIlt envIronment

spring 2012

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EDITOR IN CHIEF

Copyright © 2012 University of Pennsylvania Press.

Frank Matero

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Change Over Time AN

INTERNATIONAL OF

AND

THE

BUILT

JOURNAL

CONSERVATION ENVIRONMENT

SPRING

2012

2.1


2

Editorial F R A N K M AT E R O

ESSAYS

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CONTENTS

The Use of Ground-Penetrating Radar in the Documentation and Evaluation of Iglesia San Jose´, San Juan, Puerto Rico AGAMEMNO N GUS PANTEL

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Twenty-Five Years of Archaeological Site Inventories in the Middle East: Challenges and Perspectives GA ETAN O PALU MB O


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The Middle Eastern Geodatabase for Antiquities (MEGA): An Open Source GISBased Heritage Site Inventory and Management System D AV I D M Y E R S A N D A L I S O N D A L G I T Y

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Heritage Recording and Information Management as a Tool for Preventive Conservation, Maintenance, and Monitoring: The Approach of Monumentenwacht in the Flemish Region (Belgium) A N O U K S T U L E N S , V E E R L E M E U L , A N D N E Zˇ A Cˇ E B R O N L I P O V E C

32

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Change Over Time


EDITORIAL FRANK MATERO University of Pennsylvania

Figure 1. Painted Tower, Cliff Palace, Mesa Verde, 1934. Beginning in the 1930s, a team of American archaeologists, photographers, and architects developed a highly effective hybrid method of site documentation before and after intervention by combining the precision of large format photography with the conventions of architectural drawings. This annotated composite record anticipates the later requirements of heritage documentation, which was first realized through transparent photo-mechanical overlays and today through digital media such as geographic information systems. (Photo by Markley, courtesy National Park Service, Mesa Verde National Park)

2


Innovation has always played an important role in heritage conservation. The interdisciplinary requirements of the field have required professionals to think creatively and to employ a wide variety of techniques and methodologies. While disciplinary collaboration is well established, the technological revolution in the capture, analysis, and dissemination of information is evolving at a rapid pace, requiring constant reevaluation of the goals and objectives of heritage documentation. Mainstream technology is now available that allows professionals not only to gather and process data precisely and efficiently, but also all on compatible platforms. This is a critical requirement as an increasing number of diverse specialists with their own language and data requirements contribute to the conservation project and a more informed public demands access to that information. Previous and current efforts to address these needs include the activities of the RecorDIM (Recording, Documentation, and Information Management) Initiative, a project that developed out of four years of workshops organized by the Committee for Documentation of Cultural Heritage (CIPA Heritage Documentation) jointly sponsored by ICOMOS (International Council on Monuments and Sites) and ISPRS (International Society for Photogrammetry and Remote Sensing) from 1995 until 1999. The result of these years of work was the RecorDIM Initiative, founded in 2002 by ICOMOS, CIPA Heritage Documentation, and the Getty Conservation Institute (GCI). From the beginning the partners recognized the ‘‘critical gaps between those who provide recording, documentation, and information management tools and professionals in cultural heritage management who use the tools,’’ a reality uncovered over the course of the initial workshops in the 1990s.1 As a result, the following goals were identified: 1. To improve perception and communication in recording, documentation, and information management; 2. To integrate communication in recording, documentation, and information management activities into the conservation process; 3. To increase resources for documentation; 4. To define, develop, and promote documentation tools; 5. To disseminate information; and 6. To make available training/learning programs.2 Most cultural heritage professionals agree that the need for a more sophisticated understanding of technology is a critical one; however, ‘‘bridging the gap’’ between the MATERO

EDITORIAL

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user and provider must be addressed through education on both sides that seeks instead to narrow that gap. While heritage conservation’s unique research and management needs argue for specific requirements in documentation and recording, it is worth asking whether activities such as software development are the most appropriate place for cultural heritage organizations to invest their time and energy. Similarly, it would be foolish to embrace uncritically technologies developed for situations and applications removed from the immediate and especially long-term obligations of heritage stewardship. The promise of ultimate data capture of a resource now for future use is a seductive opportunity that should be considered in light of other requirements and often more immediate needs such as its versatility and ability to be used in simultaneous applications by a variety of specialists as well as site managers. Data that is difficult to manipulate, transfer, and migrate, no matter how exact, does not satisfy the requirements of most cultural heritage projects. Ultimately all conservation projects, especially those that require documentation and information management, must include discussions about digital tools. As long as we continue to treat digital technology as outside the conservation process or as an afterthought, we will fail to inform, manage, and educate effectively. Despite its widespread presence, the use of digital technology in the field of conservation/preservation is only recently being considered as a topic to be studied in and of itself. Many important initiatives have occurred within individual organizations; however, the time has come to begin formalizing this new and necessary component of cultural management. The expansion of courses in the application of digital media for cultural resources is now greatly needed as the next step in shaping the future of the field and its practitioners. This collection of papers, the second group to be published from SMARTdoc: Heritage Recording, Documentation, and Information Management in the Digital Age, held in Philadelphia on November 19–20, 2010, focuses on the manipulation and application of collected data for the analysis and management of cultural resources. Together with the papers of the previous issue of Change Over Time (Volume 1.2, Fall 2011), which focused on digital recording and image capture, we offer a snapshot of current thinking and applications in the recording, documentation, and information management of built heritage. While the technology will undoubtedly change, even by the time this issue is released, we believe the questions raised will continue to inform future research in the years to come.

References 1. ‘‘Recording, Documentation, and Information Management (RecorDIM) Initiative,’’ Getty Conservation Institute, http://extranet.getty.edu/gci/recordim/ (accessed March 17, 2012). 2. Ibid.

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THE USE OF GROUND-PENETRATING RADAR IN THE DOCUMENTATION AND EVALUATION OF IGLESIA SAN JOSE´ , SAN JUAN, PUERTO RICO AGAMEMNON GUS PANTEL, PH.D. Pantel, Del Cueto & Associates

Figure 1. Front facade of Iglesia San Jose´ as seen from the west. (Pantel, del Cueto & Associates)

6


The sixteenth-century church, Iglesia San Jose´, in San Juan, Puerto Rico, was placed on the World Monuments Watch List in 2004. Originally known as the Iglesia de Santo Toma´s de Aquino, it is considered by many scholars to be one of the finest and oldest examples of Gothic-influenced religious architecture built by the Spanish in the New World. Water infiltration and structural issues were at the core of the closing of the structure in 2002 after which emergency conservation measures were developed together with a long-term restoration plan. Both the development of the restoration plan and the conservation measures were enhanced by the use of groundpenetrating radar with both midrange and high-frequency antennas. Subsurface water infiltration and subsequent voids were effectively mapped to help determine patterns of rainwater travel through the stone and rubble masonry walls. Ground-penetrating radar results also provided evidence of multiple construction phases and modifications and corroborated or enhanced architectural evidence used to understand the construction sequences.

As an integral part of the long-term assessment of Iglesia San Jose´, several surveys using ground-penetrating radar (GPR) were conducted inside and outside the church to help determine conditions, the existence of physical evidence of building campaigns, and modifications to the church through time. Ground-penetrating radar is a reflection technique that works by transmitting low-powered microwave energy into a substance like the ground. The use of GPR in this project was instrumental in changing the way historic structures have been commonly studied in the Caribbean, where historic fabric investigations by architects and engineers usually involve destructive testing. The use of GPR in Iglesia San Jose´ allowed the compilation of subsurface features and conditions of the historic building fabric, not only in a nondestructive manner, but equally important, allowed the examination of larger areas than otherwise possible with harmful and irreversible techniques. GPR was selected as a way to image evidence of moisture and its distribution and to identify the building’s original foundations, crypts, and construction elements in selected portions of the church. Both the development of the restoration plan and the conservation measures were enhanced by the use of ground-penetrating radar with both midrange and high-frequency antennas.1 Four antennas were used for the GPR surveys in Iglesia San Jose´: 400 MHz, 900 MHz, 1000 MHz, and 1500 MHz.

Background The early-sixteenth-century church, Iglesia San Jose´ (San Jose´ Church), in San Juan, Puerto Rico, is the second (and possibly) oldest extant European structure in the Western HemiPANTEL

THE USE OF GROUND-PENETRATING RADAR

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sphere. The church was originally known as the Iglesia de Santo Toma´s de Aquino, and it is considered by many scholars to be one of the first and finest examples of Gothic-influenced religious architecture built by the Spanish in the New World. Water infiltration and structural issues were at the core of the building’s closing in 2002, after which emergency conservation measures were developed together with a long-term restoration plan. In 2004 it was placed on the World Monuments Fund’s World Monuments Watch List. Iglesia San Jose´ was constructed from 1532 to 1735 by the Dominican Order as the church to their adjacent monastery in Old San Juan. Throughout its 478 years, the climatic ravages of a subtropical setting and the lack of timely preventive maintenance have contributed to the cumulative toll on the building. Its closure to the public, approximately ten years ago, resulted from a safety concern by the Archdiocese of San Juan. The closing of the church served to accelerate general deterioration due in a large part to water infiltration from unchecked rainwater drainage, trapped humidity, and the encroachment of large vegetation on its roofs. In 2002 Pantel, del Cueto & Associates was contacted by the Archdiocese to assess and develop measures for the building to allow it to return to its functioning state as a parochial church and an active historic landmark. Given this charge, the church was systematically surveyed from 2003 to 2006 to determine the actual condition of its fabric, utilizing different evaluation strategies. This included systematic visual inspection of surface conditions, historic documentary comparisons, laser surveys, thermal scans, groundpenetrating radar, and materials sampling and analysis. The conservation issues of Iglesia San Jose´ presented unique problems, resulting from a complex set of construction episodes that utilized Old World templates but modified them to local materials, workmanship, and climatic conditions. Lacking any clear historical records of the various changes to the church, let alone any writings or drawings of the original construction, the condition assessment of Iglesia San Jose´ included the use of historic urban graphics that prominently showed the church to determine changes in plan as well as a structural analysis that utilized nondestructive testing and traditional documentation techniques. The assessment resulted in the establishment of a set of hypothetical building phases from the sixteenth through the eighteenth centuries, based initially on cartographic data and later on construction methodologies. Some of the first steps taken in the intervention into this historic landmark were emergency measures to reopen the natural ventilation of the church, abate the entrance of pigeons, rechannel rainwater drainage from the roofs, and most significantly, provide shoring for the church’s sections of Gothic vaulting. Consolidation of plasters containing significant early murals was also performed. The bulk of the Iglesia San Jose´ GPR surveys was conducted using a Geophysical Survey Systems (GSSI) GPR unit consisting of a digital console, a cable, and an antenna. Four antennas were alternatively used: a 400-MHz antenna, which allowed data collection to approximately three meters deep, and higher frequency 900-MHz, 1000-MHz, and 1500-MHz antennas to determine shallower subsurface architectural and/or constructive 8

CHANGE OVER TIME


Figure 2. Graphic illustration of the hypothetical building phases of Iglesia San Jose´ based on cartography and structural investigations. (Pantel, del Cueto & Associates)

sequence elements located less than a meter in depth within walls and floors.2 The data were initially examined as raw radargrams and selective survey data sets were postprocessed using GPR-SLICE software. Four distinct survey issues will be illustrated. The first is a general survey carried out to determine the viability of ground-penetrating radar for Iglesia San Jose´ and a general overview of the subsurface conditions of its interior. A second example examines the use of GPR with a high-frequency antenna to assess the construction sequence of the expansion of a lateral chapel along the southern face of the church. A third example demonstrates the application of GPR to determine the locations and extent of subsurface foundations for the structural engineers of the project. The fourth example illustrates the application of GPR as both a documentation and administrative tool in providing information for the reopening of one of the principal connections between the original sixteenthcentury convent and San Jose´ as its conventual church. A final example shows how the software and interpretation of GPR data can make a significant difference in the proper assessment and documentation of a historic structure.

The First GPR Survey—Exploratory Sounding Prior to the installation of the structural shoring of the church’s Gothic section, an initial ground-penetrating radar survey was done in January 2004 of the entire central nave to determine the viability of using ground-penetrating radar at the site, and to provide an initial evaluation of the subsurface condition of the church floors as well as the potential for crypts or structural remains. PANTEL

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Figure 3. GPR-Slice detail indicating the extent of subsurface moisture (medium gray, concentrated at right) along the southern sections of Iglesia San Jose´. (Pantel, del Cueto & Associates)

Several very important anomalies were seen in the GPR data, with the most obvious being subsurface moisture distribution as well as three crypts or tombs. Radar anomalies surrounding the easternmost set of columns along the north aisle indicated earlier footings of the interface between the early Gothic construction and the subsequent additions. The GPR-SLICE data indicated a faintly visible wall, partition, or even previous structures within the central portion of the nave to the immediate north of the main western entrance. Radar readings also showed rectilinear lines within the floor of the central nave, which suggested possible underground utilities, most likely abandoned. At the eastern end of the church where the raised altar platform begins, there were indications of foundations associated with the principal Gothic columns of the altar and that of the main vault area. What the results of this initial survey clearly showed in red (herein indicated as light gray in the black and white image) were areas of subsurface water infiltration, which is 10

CHANGE OVER TIME


identified by its horizontal distribution across the floors of the church as well as by the degree of depth of water penetration. This information was significant for the architect of the project in that these maps provided insights into the intensity of water infiltration through the rubble masonry walls, the exact location of penetration, and, given the knowledge of the subsurface soils, the potential for floor collapses in specific parts of the church. Additional information provided by the first GPR survey indicated deep remnants of potential scaffolding post molds under the barrel-arched central nave of the church. These scaffolds would have most likely been used in the central nave’s conversion from a pitched gable roof to the present barrel-vaulted nave. The apparent depths of these elements are also significant in determining the integrity of possible early Christian burials, which would have been located in what was previously the western campo santo of the conventual church.

The Second GPR Survey—Capilla de Bele´n Chapel Walls Having determined that using ground-penetrating radar data within the church was potentially productive, a second GPR survey was conducted in June 2006 to search for evidence of multiple construction phases or modifications and to corroborate or enhance architectural evidence used to understand the construction sequences. Specifically, it was not known whether the modification of the Capilla de Bele´n (Bele´n chapel) to the south of the Gothic section was completed as an extension of a previous construction or a completely ‘‘new’’ construction. The west-facing wall of the Capilla de Bele´n was surveyed using a 1000-MHz antenna systematically pulled along transects 25 centimeters apart, and the data were postprocessed in GPR-SLICE to create an animated map of anomalies3 that may be associated with construction events. Based on the radargram data, there was no evidence of multiple construction episodes for this wall, even though the previous architectural analysis indicated an expansion of the chapel in this direction. Hence, based on the GPR data, a possible scenario for the lack of sequential construction expansions for this wall may have been a consequence of the complete removal of a previous wall and the subsequent construction of a new wall for the expansion.

The Third GPR Survey—Structural Foundations In February 2007 a third GPR survey was carried out both inside and outside the church along the principal walls to determine the locations and nature of structural foundations so as to assist the structural engineers4 in their development of dynamic models. Single profiles were done with a 400-MHz antenna immediately along the inside and outside walls of the church. Using the raw radargrams, areas indicating evidence of subsurface anomalies were identified as potential loci for building foundations. Based on these readings, a set of test excavations were proposed for ground-truthing of the data. The use of point-specific excavations was important, not just from a cost/time factor, but more importantly, it allowed the Archdiocese’s request for the government permit for archaeoPANTEL

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Figure 4. GPR-Slice data set showing subsurface anomalies indicative of early walls in the central nave area (top) and anomalies which appear to be traces of scaffolding footings installed during the construction of the central nave barrel vault (bottom). (Pantel, del Cueto & Associates)

logical testing to be significantly expedited. This was a critical factor given the known potential for encountering early Christian burials within and around the church itself. The results of the GPR survey and the test results were provided to the structural engineers and project architect and facilitated the development of the restoration plans for both the Gothic areas as well as the remainder of the church.

The Fourth GPR Survey—Convento de los Dominicos Bounding Wall When the secularization of many religious buildings was imposed by the Spanish Crown in the middle of the nineteenth century in Puerto Rico, the primary connections between the Convento de los Dominicos (Dominican Convent) and Iglesia San Jose´ were sealed. Although the original doors and archway of the connection was left intact, bricks and 12

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Figure 5. Using a 1000-MHz antenna, Dr. Dean Goodman ran GPR transects along the western wall of the Capilla de Bele´n (top); and a GPR-Slice image of the high-frequency antenna data superimposed on the west wall of Capilla de Bele´n showing the absence of multiple construction episodes (bottom). (Pantel, del Cueto & Associates)

rubble masonry were used to infill the doorway, sealing the wall of San Jose´ and the southern gallery of the convent, which was subsequently converted into a military barracks. Hence, church and state became physically separated. Later-twentieth-century interventions added significant coverings of cement plasters to the convent walls as the structure was converted into the headquarters of the Institute of Puerto Rican Culture in the 1950s. A final recent conversion of this building was undertaken to adapt the convent into the National Gallery of Art of Puerto Rico. Through all these modifications, the end result has been the loss of the physical and conceptual relationship between Iglesia San Jose´ and the original Convento de los Dominicos. Rediscovered within San Jose´ in the late 1970s, the doorway remained as a vestigial opening without function, while the convent’s southern gallery continued to be a single PANTEL

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Figure 6. Examples of the documentation of controlled minimal subsurface excavations carried out to corroborate GPR survey data for structural foundations. (Pantel, del Cueto & Associates)

blank wall, devoid of any relationship to its sister building. In an effort to both reestablish the conceptual ties of the two structures for the twenty-first century and, equally important, to provide a significant point of natural ventilation, the decision was made to reopen the doorway that had been sealed for more than 150 years. What then appeared to be a relatively simple operation of breaking open the doorway soon became an administrative issue between the church and the Institute of Puerto Rican Culture who owned the new National Gallery. Although the general location of the opening on the convent side could have been determined by lineal measurement from the front fac¸ades and/or by simple drilling from the church side, the government officials were wary of how the opening would affect the visual aspect of the new gallery walls. In an effort to assuage these concerns, the GPR data were able to provide the scientific documentation of exactly where the limits of the opening would be on the convent side. A fixed gate for the reopened doorway was agreed upon beforehand as protection for both institutions. 14

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Figure 7. Documentation showing the location and condition of the principal access door between the north wall of Iglesia San Jose´ and its adjoining convent, which was sealed in the nineteenth century. (Pantel, del Cueto & Associates)

A single profile GPR survey was done on the full length of the southern corridor wall of the National Gallery. The results of the GPR survey provided clear evidence of the location and dimensions of the original convent-church doorway along the National Gallery wall and allowed the architect to submit a set of drawings with the GPR readings and the exact location of where the wall would be reopened. Based on this information, obtained through a nondestructive and precise method without having to break any wall surfaces initially, the permit was given by the Institute to allow the doorway to be reopened. As a final result, the connection between the convent and its church are now clearly seen by visitors to both the National Gallery and the church, as well as providing needed ventilation for the stability of San Jose´.

A Final Example—Capilla de Bele´n Floor To determine the subsurface condition of the Capilla de Bele´n, a GPR survey of the floor of this space was recommended. Although the initial purpose of this survey area was to determine subsurface moisture and the potential for Gothic-period stepped foundations in the southeastern corner of the chapel itself, the most significant event recorded by the GPR survey within the Capilla de Bele´n were early walls adjacent to the northern entrance to the chapel. As can be seen in the GPR-SLICE data, a small rectangular feature appears near the entrance to the chapel at approximately one meter below the present surface of PANTEL

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Figure 8. GPR-Slice data at one meter below surface of the floor of the Capilla de Bele´n showing the location of a right-angle subsurface anomaly. This feature is shown superimposed over the present ground floor plan. The alignment of this subsurface anomaly appears to indicate an original southern extension of the early sixteenth-century Gothic fac¸ade of Iglesia San Jose´. (Pantel, del Cueto & Associates)

the floor. When these data were overlaid onto the present floor plan by the architects, the location and configuration of this anomaly indicated the presence of a clear extension of the original sixteenth-century Gothic fac¸ade extending to the south into what is now the Capilla de Bele´n. This final example is a classic demonstration of how the selection and use of specific software can make a significant difference in the interpretation of the data collected by a GPR hardware unit.

Final Comments and Summary The sequence of ground-penetrating radar surveys carried out in San Jose´ has shown that evidence of construction campaigns and modifications are still visible in the subsurface archaeological record. Anomalies and subsurface features are evident in both the raw radargrams as well as in the data processed using GPR-SLICE software. The use of GPR as a nondestructive tool in condition surveys allows researchers to cover significantly larger areas than destructive and irreversible methods. The use of the newer technologies in the Caribbean has been extremely limited in large part due to the common belief that the techniques require expensive equipment and sophisticated technical know-how. Often, this is further exacerbated by the haphazard approach to interventions of historic buildings. Government agencies involved in the regulation of historic properties usually favor familiar methods to study or resolve a specific issue over that of 16

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newer methods aimed at identifying causality prior to any intervention. The ‘‘quick-fix’’ resolves only the immediate problem in a specific area, but does not provide a solution to the overall condition nor does it identify the problem’s source. The practice of these inappropriate interventions into the historic fabric, without understanding the causes of the problems through systematic survey and analysis, most often results in the accelerated and/or expanded deterioration of the property. Nondestructive testing, such as GPR, provides insights into problems occurring below the surface without having to destroy historic fabric and can be cost-effective in maintaining the integrity of singular historic evidence such as that of Iglesia San Jose´. As in all scientific work, negative data are just as valuable as positive data; therefore, the application of ground-penetrating radar, while not a panacea, can greatly help in determining not only areas that are problematic, such as subsurface water infiltration, but can also show those areas that are devoid of any conservation issues. In this sense, the information provided by systematic and/or problem-specific GPR surveys in historic sites and structures can be just as much an administrative as a documentation tool.

Acknowledgments I would like to thank the following: Architect Beatriz del Cueto, FAIA, for all the background information and her unparalleled collaboration in all phases of the work. Dr. Kent Schneider and Dr. Dean Goodman gave their time and knowledge to successfully carry out the ground-penetrating radar projects and did the processing and analysis of the Iglesia San Jose´ data sets. Dr. Dean Goodman is also to be thanked for his development and generous support in using his GPR-SLICE software. Dr. Paola A. Schiappacasse who assisted in all phases of the archaeology programs and in the GPR surveys. The Archdiocese of San Juan for their support and interest in protecting and restoring this unique New World structure. The architecture students from the Polytechnic University of Puerto Rico who helped in the GPR surveys carried out in the Plaza San Jose´ adjacent to the southern entrance to Iglesia San Jose´. Prof. Frank Matero and Dr. Mario Santana for organizing SMARTdoc at a time when technology and documentation need to take stock of the past and future.

Further Reading Conyers, Larry B., and Dean Goodman. Ground Penetrating Radar: An Introduction for Archaeologists. (Walnut Creek, Calif.: Altamira Press, 1997). Del Cueto, Beatriz and Yaritza Herna´ndez. Proyecto de Conservacio´n Iglesia San Jose´ Data Histo´rica: Cronologı´a, Gra´ficas y Bibliografia. Unpublished technical report, 2004. Del Cueto, Beatriz, Agamemnon G. Pantel, et al. Iglesia San Jose´ Conservation Project, Condition Assessment Report. Unpublished technical report, 2006. Goodman, Dean, Kent Schneider, Yasushi Nishimura, Salvatore Piro, and Agamemnon G. Pantel. ‘‘Ground Penetrating Radar Advances in Subsurface Imaging for Archaeology.’’ In Remote Sensing in Archaeology, ed. James Wiseman and Forouk El-Baz. (New York: Springer Press, 2006), 375. GPR-SLICE, http://www.gpr-survey.com/gprslice.html. Pantel, Agamemnon G. Iglesia San Jose´ Ground Penetrating Radar Survey and Interpretation, Viejo San Juan, Puerto Rico. Unpublished technical report, 2008.

PANTEL

THE USE OF GROUND-PENETRATING RADAR

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Pantel, Agamemnon G. ‘‘Los Edificios Mas Antiguos del Nuevo Mundo. El Caso de la Iglesia de San Jose´ en San Juan de Puerto Rico: Estudios Previos y Proyecto de Conservacio´n.’’ In Actas del Seminario: El Edificio en la Ciudad Histo´rica: Casos y Criterios de Intervencio´n, Universidad Polite´cnica de Valencia, Programa de Ma´ster en Conservacio´n del Patrimonio Arquitecto´nico, Valencia, Espan˜a. Unpublished proceedings, 2008. Pantel, Agamemnon G. and Paola A. Schiappacasse. Prospeccio´n Remota con Radar y Pruebas Arqueolo´gicas Estructurales, Iglesia San Jose´, Viejo San Juan, Puerto Rico. Unpublished technical report, 2009. Robert Silman Associates. ‘‘Iglesia de San Jose´ San Juan, Puerto Rico: Preliminary Summary of Recommendations and Observations regarding the Structural Conditions of the Iglesia San Jose´.’’ Unpublished technical report, 2003.

References 1. The survey designs, data collection, processing and analyses of the surveys were done by archaeologists Dr. Kent Schneider and the author, in collaboration with geophysicist and GPR-SLICE software developer Dr. Dean Goodman. 2. The higher the antenna frequency, the shorter the wavelength and penetration depth. A very good discussion of time-depth analysis can be found in Conyers and Goodman (1997), 107–135. Depth estimates for targets identified with each antenna were achieved using the hyperbola-fitting method provided in GPR-SLICE software. For the Iglesia San Jose´ surveys, depth to targets was estimated using a dielectric constant (velocity) for the time-to-depth conversion. True depth may vary from the apparent depth due to lateral and vertical variations in the dielectric constant and the depth of the targets sought. Resolution of targets with the 1500-MHz antenna was good to 20 centimeters in depth, the 1000-MHz antenna to 40 centimeters, and the 900-MHz antenna to approximately 1.00 meter in depth. The 400-MHz antenna was used for accurate resolution to approximately 2.0 meters deep, beyond which the antenna signal was attenuated. 3. An ‘‘anomaly’’ in a GPR data set is any disturbance in the subsurface matrix. 4. The structural engineers for the project were Robert Silman Associates, New York.

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