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12 the limitations of not being able to work directly under the 2. To investigate the capabilities of the Interphase scan- bridge in most cases and trying to resolve the accuracy- ning sonar and its potential application to bridge scour versus-cost issue. The easiest way to achieve sub-meter and work; even centimeter accuracy is to use a survey grade GPS 3. To research and develop an articulated arm device ade- receiver; however, with an investment of at least $20,000 for quate for smaller bridges.; each receiver, this approach is limited by cost and the poten- 4. To research the use of low-cost GPS for positioning in tial risk of losing the device when working in the difficult con- scour monitoring applications; and ditions presented by flood-flow monitoring. Low-priced GPS 5. To research and develop data collection software suit- receivers (< $7,500) can provide meter to sub-meter accuracy able for laptop computer application that facilitates data with differential positioning, which would be adequate for collection, analysis, and reporting. horizontal position in many cases, but certainly not for verti- cal. However, the scour measurement can be referenced to the It was recommended that off-the-shelf products be used, water surface elevation or a reference elevation on the bridge where possible, for each component of the above systems. This deck, with the GPS data used only for horizontal position. would facilitate the purchase, construction, and repair of the Therefore, if a local DPGS signal is available (e.g., from the resulting portable scour monitoring equipment and keep the NDGPS network or some other source) a lower priced GPS total cost reasonable. The following paragraphs summarize unit on the deployment platform could be used, minimizing the Phase II objectives for each alternative. the cost risk while providing relatively accurate data. For bridge deck-based deployment using cranes or booms, horizontal position can be well controlled and referenced to Alternative 1--Minnesota Boom Setup the abutment. Methods of locating horizontal position across The objective of this task was to document the winch con- the bridge that are adaptable to automated data collection cept developed by Minnesota DOT and evaluate potential include distance measuring wheels and low-cost lasers. improvements to the design and/or how it is used in scour mon- itoring. This could include evaluating the various components Data Storage Devices used to fabricate the winch system, the mounting concepts for the winch, and the use of the winch on different types of cranes. Data storage devices include data loggers, laptop com- Of interest was the application of this concept to a pickup truck, puters, and, more recently, PDAs. Data loggers are generally rather than a large flatbed truck. not very user-friendly; laptop computers are susceptible to damage in a field-based application; and PDAs may be too limited in capability. If local telemetry were used to transmit Alternative 2--Interphase Scanning Sonar data from the deployment platform, the best approach might This objective of this work was to evaluate the use of rela- be a laptop computer, with the operator at the side of the tively low-cost Interphase scanning sonar for scour monitoring, bridge, preferably in a vehicle. In this way, the computer can based on limited testing under laboratory or field conditions. be used for both data collection and data reduction, perhaps in a real-time mode, while being protected from the environment. The use of PCs is much more common than it was even 5 years Alternative 3--Articulated Arm Devices ago, and most people have a comfort level and a working knowledge of their operation. In contrast, PDAs are still Based on work completed by the FHWA on an articulated evolving and changing rapidly, making it more difficult to arm device, the objective of this work was to develop an alter- develop a system for a specialized application, such as bridge native design that is smaller, less complicated, and more cost- scour data collection, without it becoming quickly outdated by effective. Different types of commercially available articulated the next generation of devices. arms will be investigated and methods for tracking the angular position of the arm evaluated. A prototype device will be built and tested in detail. PHASE II WORK PLAN Based on the literature review and Phase I findings, a Alternative 4--Low-Cost GPS detailed work plan was developed for Phase II. The alterna- Positioning System tive technologies selected for further research, development, and testing under the Phase II work plan were as follows: The objective of this testing was to evaluate the application of a lower cost GPS receiver for bridge scour monitoring. 1. To document the custom-fabricated boom and winch Field testing around a bridge will be used to establish guide- setup developed by Minnesota DOT and any variations lines for when and where this type of positioning will work on that design; and when it should not be considered.