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The Use of Ground-Penetrating Radar in the Documentation andEvaluation of Iglesia San Jos, San Juan, Puerto Rico

Agamemnon Gus Pantel

Change Over Time, Volume 2, Number 1, Spring 2012, pp. 6-18 (Article)

Published by University of Pennsylvania Press

DOI: 10.1353/cot.2012.0006

For additional information about this article

Access Provided by UNIVERSITY OF THE ARTS, LONDON at 02/10/13 8:12PM GMT

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6

THE USE OF GROUND-PE NETR ATI NG RADAR IN THE

DOCUMENTATION AND EVALUATION OF IGLESIA SAN

JOSE, SAN JUAN, PUERTO RICO

AG AM EM NO N GU S PAN TE L, PH .D.

Pantel, Del Cueto & Associates

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

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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 theIglesia de Santo Tomas 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 ground-

penetrating 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 tech-

nique 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 investiga-

tions by architects and engineers usually involve destructive testing. The use of GPR in

Iglesia San Joseallowed the compilation of subsurface features and conditions of the his-

toric building fabric, not only in a nondestructive manner, but equally important, allowed

the examination of larger areas than otherwise possible with harmful and irreversibletechniques. GPR was selected as a way to image evidence of moisture and its distribution

and to identify the buildings 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 JoseChurch), in San Juan, Puerto

Rico, is the second (and possibly) oldest extant European structure in the Western Hemi-

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8 C H A N G E O V E R T I M E

sphere. The church was originally known as the Iglesia de Santo Tomas 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 struc-

tural issues were at the core of the buildings 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 Funds 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 con-

tributed 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 infiltra-

tion 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 assessand 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 sur-

face conditions, historic documentary comparisons, laser surveys, thermal scans, ground-

penetrating radar, and materials sampling and analysis. The conservation issues ofIglesia

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 con-

struction 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 churchs 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 collectionto approximately three meters deep, and higher frequency 900-MHz, 1000-MHz, and

1500-MHz antennas to determine shallower subsurface architectural and/or constructive

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Figure 2. Graphic illustration of the hypothetical building phases ofIglesia San Josebased 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 postpro-

cessed 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 expan-

sion of a lateral chapel along the southern face of the church. A third example demon-

strates 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 informa-

tion for the reopening of one of the principal connections between the original sixteenth-

century 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 Sur veyExplorator y Sounding

Prior to the installation of the structural shoring of the churchs 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 aninitial evaluation of the subsurface condition of the church floors as well as the potential

for crypts or structural remains.

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1 0 C H A N G E O V E R T I M E

Figure 3. GPR-Slice detail indicating the extent of s ubsurface moisture (medium gray, concentrated at

right) along the southern sections ofIglesia 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 foot-

ings 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 struc-

tures 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

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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 knowl-

edge 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 naves 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 santoof the conventual

church.

The Second GPR Sur veyCapilla de Belen 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 theCapilla de Belen(Belen chapel) to the south of

the Gothic section was completed as an extension of a previous construction or a com-

pletely new construction.

The west-facing wall of the Capilla de Belenwas surveyed using a 1000-MHz antenna

systematically pulled along transects 25 centimeters apart, and the data were postpro-

cessed 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 indi-

cated 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 Sur veyStructural 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 subsur-

face 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 useof point-specific excavations was important, not just from a cost/time factor, but more

importantly, it allowed the Archdioceses request for the government permit for archaeo-

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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 Four th GPR Sur veyConvento 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 betweenthe 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

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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 Belen (top); and a GPR-Slice image of the high-frequency antenna data superimposed on the

west wall ofCapilla de Belenshowing 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 bar-

racks. 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 under-

taken 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 rela-

tionship betweenIglesia San Jose and the originalConvento de los Dominicos.Rediscovered withinSan Jose in the late 1970s, the doorway remained as a vestigial

opening without function, while the convents southern gallery continued to be a single


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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 impor-

tant, 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 facades 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 con-

cerns, the GPR data were able to provide the scientific documentation of exactly wherethe 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.

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Figure 7. Documentation showing the location and condition of the principal access door between the

north wall ofIglesia 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 Gal-

lery 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 providingneeded ventilation for the stability ofSan Jose.

A Final ExampleCapilla de Belen Floor

To determine the subsurface condition of the Capilla de Belen, 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 Belenwere early walls adjacent to the northern entranceto 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


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Figure 8. GPR-Slice data at one meter below surface of the floor of theCapilla de Belen 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 facade ofIglesia 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 facade extending to the south into what is now the

Capilla de Belen.

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 techni-

cal know-how. Often, this is further exacerbated by the haphazard approach to interven-tions 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

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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 Conservacion. In Actas del Seminario:

El Edificio en la Ciudad Historica: Casos y Criterios de Intervencion, Universidad Politecnica de Valencia,

Programa de Master en Conservacion del Patrimonio Arquitectonico, Valencia, Espana. Unpublished pro-

ceedings, 2008.

Pantel, Agamemnon G. and Paola A. Schiappacasse. Prospeccion Remota con Radar y Pruebas Arqueologicas

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 Recom-mendations and Observations regarding the Structural Conditions of the Iglesia San Jose. Unpub-

lished 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 devel-

oper 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), 107135. Depth

estimates for targets identified with each antenna were achieved using the hyperbola-fitting methodprovided in GPR-SLICE software. For theIglesia San Josesurveys, depth to targets was estimated using

a dielectric constant (velocity) for the time-to-depth conversion. True depth may vary from the appar-

ent 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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