Browsing by Subject "Snow sensing"

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    Detection of Water and Ice on Bridge Structures by AC Impedance and Dielectric Relaxation Spectroscopy Phase I
    (University of Minnesota Center for Transportation Studies, 2009-04) Evans, John F.
    We have carried out a preliminary evaluation of two approaches to low-cost sensing systems for monitoring ice and water on bridge deck surfaces. These sensing systems are based on the measurement of impedance of the sensor in contact with or close proximity to ice, water or aqueous solutions of deicing chemicals. Impedance analysis at lower frequencies allows for the determination of the presence of solutions of deicing electrolyte (a sort of “conductivity measurement"), while high frequency dielectric relaxation using time domain reflectometry (TDR) probes the physical state of precipitation and deicing chemicals on the deck or road surface (via dielectric relaxation). While we originally expected that both measurements would be required to reliably determine the condition of a bridge deck surface with regard to the presence of frozen water or deicing solutions, we have found that the TDR approach is adequate for this task. This suggests that a significant reduction in both the cost of development of practicable sensors and supporting software/electronics can be realized, as well as the ultimate cost of deploying a system based on TDR alone can be realized. As such, TDR becomes the focus for the next phase of development of these sensors.
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    Detection of Water and Ice on Bridge Structures by AC Impedance and Dielectric Relaxation Spectroscopy Phase II
    (Intelligent Transportation Systems Institute, Center for Transportation Studies, 2013-08) Evans, John F.
    During Phase I of this project, we have carried out preliminary evaluation of a novel approach to low-cost sensing systems for monitoring ice, water and deicing solutions on road bridge deck surfaces. Our initial approaches included the techniques of alternating current impedance and dielectric relaxation spectroscopy of responses from simple passive metal sensors. These preliminary results indicated that the second approach of dielectric relaxation spectroscopy was far more promising. Furthermore, likely implementations would be significantly more economical using lower-cost electronics modules connected to passive sensors. Our choice for implementation of dielectric relaxation spectroscopy is based on the measurement of high-frequency components of pulse waveforms reflected from the sensor and using time domain reflectometry (TDR). The information content of these waveforms is strongly influenced by the dielectric properties of the media of interest (ice, water or aqueous solutions of deicing chemicals) in contact with or in close proximity (microns) with passive metal conductors, which comprise the sensor. These high-frequency dielectric relaxation measurements using TDR probe the physical state of precipitation and deicing chemicals on the deck or road surface by the detailed examination of the frequency response waveforms returned after the application of a fast rise-time excitation pulse. Signal processing of the acquired waveforms involves taking the derivative of the response followed by digital filtering and subsequent wavelet analysis to emphasize and distinguished low vs high frequency components of the waveforms reflected from the sensors. Determination of the state and nature of the precipitation, solutions or air in contact with a given sensor is made on a statistical basis via correlation of responses to calibration waveforms collected under known conditions for a given sensor. The software to carry out these signal processing tasks in implemented using LabVIEW.
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    Detection of Water and Ice on Bridge Structures by AC Impedance and Dielectric Relaxation Spectroscopy, Phases III and IV: Continued Field Testing and Refinement of Novel Water and Ice Sensor Systems on Bridge Decks
    (Intelligent Transportation Systems Institute, Center for Transportation Studies, 2013-08) Evans, John F.
    During Phases III and IV of this project it was determined that the physical attributes of the prototypes developed during the earlier work was inappropriate for bridge deck installations. Mn/DOT engineers required that they be planar and not require drainage through the deck. As RWIS platforms had been widely deployed on decks throughout the state, we decided to adhere to the RWIS geometric format. This necessitated a significant re-engineering of the sensor hardware before installation and testing at remote bridge sites could proceed. To that end extensive development of a robust sensor meeting these requirements was developed and tested without compromise to the earlier performance results. In large part the maintenance of performance was achieved through a significant modification of the software to include Wavelet analysis of the raw data in the determination of surface state of the sensor platform (ice vs air vs water vs electrolyte present on the sensing electrode structure). The combined regression results for raw TDR responses treated by three analysis procedures are shown to give rise to very reliable results. Unfortunately, remote field testing of sensors installed on bridge decks was not accomplished.