GPS STRUCTURAL MONITORING

Physical changes to USS Arizona’s hull are being monitored using a series of high-resolution GPS points established on the vessel during June 2001. SRC archeologists partnered with the US Army’s 29th Engineer Battalion Survey Platoon, who provided state-of-the-art dual-frequency GPS receivers, to set a series of monitoring points across Arizona’s deck. Archeologists set stainless steel studs in selected locations, and then leveled a large, underwater tripod, designed by SRC, over each point. Extension poles set on top of the tripod extending above the water’s surface allowed the GPS antenna to be placed precisely over the desired point. Using advanced survey techniques, the Army surveyors were able to collect points with sub-centimeter accuracy in three dimensions. The plan was to resurvey these points periodically to determine if, and how, the ship is moving, shifting and settling.

The first reoccupation of the GPS monitoring points was scheduled for November 2003. In the intervening two-year period, the NPS acquired the necessary instruments to complete the survey in-house. Mr. Tim Smith from the NPS-GPS Program and Mr. Mark Duffy from Assateague Island National Seashore provided instruments and expertise to complete the operation. The first problem encountered was that most of the stainless steel studs, which were encased in epoxy, had corroded away. The epoxy did not prevent electrolytic corrosion of the stainless steel imbedded in the mild steel of the deck plates. Each point was reoccupied as best as possible, but we made the decision that new points not subject to corrosion must be established (Figure 13 and Table 1). PVC was used, and each new point was established adjacent to the original point. Each of these new points was then surveyed and will become the permanent monitoring points (Figure 14).

Figure 13. GPS tripod set on a 2001 monitoring point.

Table 1.

Figure 14. NPS archeologist installing new GPS monitoring point (right) adjacent to the old point (left).

Although the accuracy of each point was mathematically calculated to about 0.5 cm, it became clear that a more conservative threshold of change should be applied to future monitoring relocations. Because of environmental conditions and differences in equipment and stadia variations, we determined a more realistic threshold was 10 cm. Errors of up to 10 cm could be caused by instrument error, set-up error, or most likely, nearly imperceptible antenna movement caused by water movement. Consequently, any observed change that is less than 10 cm cannot be reliably attributed to actual movement of the ship; however, corroborative evidence would be sought for any level of change.

GEOLOGICAL ANALYSIS

A key component to the overall USS Arizona and Utah research strategy is an investigation of the geological substrate surrounding and beneath the hull. To be accurate, future predictions regarding structural stability, such as those produced from the FEM analysis, and interpretation of GPS monitoring-point movement must control for geological support variables. Hull stability is directly affected by the stability of sediments supporting Arizona, so seismic survey data will be combined with detailed core analysis to provide a comprehensive picture of the geologic substrate surrounding and beneath Arizona’s hull. An NPS/USGS team conducted subbottom profiler survey in August 2002. Based on that data, four locations around USS Arizona were chosen for geological coring.

Geological Core Collection

In November 2003, NPS-SRC collaborated with Dr. Rob Kayen and Mr. Brad Carkin from the USGS’s Western Region Coastal and Marine Geology Program. The joint NPS/USGS team worked with an environmental contractor from Honolulu, Ernest K. Hirata & Associates, Inc. to collect geological cores from around Arizona (Figure 15). Because of field exigencies, primarily encountering very hard substrate in the first boring, only three of the four planned cores were collected. The three borings were drilled to depths ranging from 15.2 to 21.3 m below the harbor bottom. The borings were drilled using portable drilling equipment mounted on a temporary barge. Continuous sampling was performed from the harbor bottom down to the maximum depths drilled in all borings (Hirata 2003).

Figure 15. Geologial coring operations, November 2003.

The recovered cores will be split longitudinally and their stratigraphy described. Sub-samples of the cores will be taken and analyzed for grain size according to American Society for Testing and Materials (ASTM) protocol ASTM D-422-63 (Standard Test Method for Particle-Size Analysis of Soils). In addition, the core sediments will be analyzed for structural characteristics according to either ASTM D2166-00 (Standard Test Method for Unconfined Compressive Strength of Cohesive Soil) or ASTM D2850-95 (Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils). Lead-210 (210Pb) and/or Cesium-137 (137Cs) radiometric sediment dating will also be completed to determine net sedimentation rate and variation. In addition to directly measurable data on the stability of geological strata surrounding USS Arizona, these cores will also provide stratigraphic correlation for precise subbottom profile record interpretation.

GEOGRAPHIC INFORMATION SYSTEM DEVELOPMENT

Geographic Information Systems (GIS) allow researchers to incorporate different types of data such as maps, plans, graphs, video and photographs into a single, cumulative, spatially referenced database for rapid display and manipulation. Primary electronic data are being consolidated into a single GIS database, including existing plans and technical drawings, photographs and results from archeological fieldwork.

During summer and fall 2003, NPS-SRC contracted with Northrop-Grumman Mission Systems (NGMS) of Lakewood, Colorado, to begin development of a GIS project that could incorporate the approximately 8,000 individual ships’ plans we have collected and scanned. The first step was to digitize base maps of each of Arizona’s deck levels. Simultaneously, NGMS created a geodatabase of USS Arizona that includes all information for each cabin and space available on the plans—each object, space or cabin is a digitally separate entity with all attributes linked to it through the geodatabase. Using these base maps and geodatabase, scanned ship’s plans can be "linked" to their appropriate object or location on the ship. Next, the NGMS team "developed an ArcIMS website to serve annotated vector polygon layers of the USS Arizona that logically track associations to a database of digital reference imagery. The web map is currently a prototype as it was developed with limited hours and remaining budget from the USS Arizona geodatabase creation" from FY03 Legacy funding. This spatial web portal prototype is a useful proof-of-concept that demonstrates imagery linked to features on the decks of the USS Arizona as well as image search and display functionality (Figure 16) (Brown 2003).

Figure 16. USS Arizona web portal system architecture schematic.

The NGMS report goes on to describe in more detail the prototype created:

Map Display

The web site currently provides functionality to view all 8 layers of the USS Arizona, query for specific features in each layer, identify features in each layer (name and description fields are most useful), turn layers on and provides for standard interactive map tools such as pan and zoom. Each layer is rendered with a 30% transparency so that deck features below the current deck may be seen "through" the top most deck that is displayed. The decks are accurately ordered in the table of contents from top to bottom. All standard web map functions are included in this HTML map service.

Document Management

The prototype website has two custom functions that allow scanned engineering drawings to be viewed through the web interface. These tools are located on the left frame under the title "Access Images" and are names: by Feature and by Query. The first tool enables the user to select a feature on a deck of the ship and query the SQL Server 2000 Database for images associated to that feature. The system architecture schematic details this process.

If multiple images are related to that one feature (room or gun turret for example) then a list of images is returned with their description. The user selects one of the images and it opens a new browser window to view the image. The prototype utilizes Lizard Tech’s loss-less image compression format for image storage and viewing. A Lizard Tech browser plug-in is required for viewing the images in a standard web browser. A link to the download site is provided on the interface.

The second custom tool (Access Images by Query) queries the database directly to produce a unique list of image themes. The user chooses a theme and is returned a subsequent list of all the images and their descriptions that fall under that theme. As the user selects an image, a new browser window is spawned to display the image.

A good deal of time was spent creating metadata for each image in the database. This metadata is what enables the document management process to work. Each image was described and given a subject or "theme" as well as linked to specific features in the 8 levels of the geodatabase by a unique feature-id (key field). Two tables were created to enable this process (Brown 2003).

The next step in the process is to refine the project and database, eventually incorporating all scanned plans from Arizona, and porting the project to an NPS network, which would allow mobile and remote access to the plans by various researchers and the public.

CONCLUSIONS

The present USS Arizona project builds upon earlier research conducted on the site by the NPS-SRC. The current project was initiated in 1998, when SRC began developing a multdisciplinary research design intended to be a comprehensive analysis of Arizona’s corrosion and deterioration, providing information for its long-term preservation and to minimize risk to the environment from oil release. The current NPS/Department of Defense partnership has allowed the research to move forward in a substantial way through the Legacy Resources Management Fund. This continuing project will ultimately allow managers to make informed decisions about Arizona’s future based on solid scientific evidence. Fieldwork and data analysis described in the 2002–2003 Legacy Project Proposal is progressing as planned. Work on additional products, such as an interim report, video report, professional seminar and analysis of remote monitoring technology is on-going and will be completed should funding levels allow continuation of the planned research program.

Brown, M.
2003 USS Arizona Memorial Web GIS Prototype Report and Recommendations. Northrup Grumman Mission Systems, October 27, 2003.

Graham, A.
2003 The USS Arizona and Bunker C Fuel Oil: An Environmental Study, M.S. Thesis, Molecular and Cellular Biology and Pathobiology Program, Marine Biomedicine and Environmental Sciences, Medical University of South Carolina, Charleston.

Hirata, E. K.
2003 Drilling Services for National Park Service USS Arizona Project. Ernest K. Hirata & Associates, Inc. W.O. 03-3832, December 17, 2003.

Johnson, D. L., J. D. Makinson, R. de Angelis, B. Wilson and W. N. Weins
2003 Metallurgical and Corrosion Study of Battleship USS Arizona - USS Arizona Memorial - Pearl Harbor. University of Nebraska, Lincoln.