The Porous Media group at NCPA, currently led by Dr. Craig Hickey, studies the propagation of sound in heterogeneous media such as soil and sand and the interaction between atmospheric born sound and the ground. Porous media propagation is an important factor in a wide range of problems. This group has studied the use of acoustic waves to detect buried objects and structures such unexploded ordinances, IEDs, and tunnels. These methods often use laser based detection schemes for measuring the vibration of the ground. These laser techniques have been expanded to study explosive residue detection from a safe distance and the use of multiple laser beams to acquire vibration data over an array of points on the surface.
The Porous Media group has also studied the use of acoustics to non-destructively determine the structural health of earthen levees and dams, measure the sediment payload carried by rivers and streams, accurately count fish stock in real time, and characterize Rayleigh (surface) wave propagation in a variety of soil types.
- NCPA is developing methods for characterizing and mapping of the spatial distribution and thickness of layers of surface soil or dam/levee materials using a laser Doppler vibrometer (LDV)-based acoustic technique and a multi-channel analysis of surface waves (MASW) method. The MASW uses surface acoustic waves (Rayleigh waves) to explore the soil surface and soil profile in terms of shear wave velocity. This method provides higher spatial resolution, faster scanning speed, and a mobile capability for soil profile exploration.
- NCPA completed a long-term field soil survey showing significant correlation between acoustic parameters and soil properties undergoing changes due to climate and seasonal influences. The MASW method discussed above is being adapted to measure the temporal variation in soil properties due to moisture.
- NCPA is developing acoustic technologies for the integrity assessment of small earthen dams. Integrity assessment requires information about the impounded sediment and the structural stability of the dam. Acoustic sub-bottom field surveys were conducted on a Mississippi oxbow lake to determine the spatial distribution of accumulated sediment. Compressional and shear wave surveys were conducted on a previously studied small earthen dam. Compared with previous results on this dam, the additional loading on the dam associated with higher water levels appears to enhance the detection of internal anomalous zones using the seismic tomograms. This is also consistent with the results obtained from previous time-lapse surveys carried out during an internal erosion experiment at the USDA Hydraulic Engineering Unit. NCPA was awarded a contract under the Department of Homeland Security/Department of Energy Southeast Regional Research Initiative (SERRI) for research in geophysical methods to assess and monitor earthen dams and levees. This effort encompasses modeling, laboratory work, and field testing at the USDA Hydraulic Engineering Research Unit.
- The highly successful NCPA program in Human Signatures for Personnel Detection has been transitioned from US Army Research Office to the US Army Armament Research, Development, and Engineering Center (ARDEC) for continued research to further define and expand capabilities. Highlights of this year include an extensive data collection exercise that included UM-developed sensors that was held jointly with the US Army Research Laboratory and ARDEC. Other significant accomplishments include modeling and experiments on the contribution of specific human body parts on the Sonar signal for walking humans. This shows promise for a number of applications including human detection for security purposes and biometrics for medical purposes.
- NCPA completed a research program in active tunnel detection using seismic refraction techniques. This was an international program conducted in collaboration with the University of Alberta (Canada). In this year, data were conducted at tunnel sites having different construction architecture, and different depths, sizes and shapes. DHS has indicated an interest both in surveys of additional border sites and of expanding the research program in future years.
- NCPA is conducting research for standoff acoustic detection of mines buried in littoral zones (inland, on beaches, and in sediment in shallow waters) using standoff laser based methods such as laser Doppler vibrometry and digital speckle pattern shearing interferometry (DSPSI). NCPA was awarded a Defense University Research Instrumentation Program grant to purchase a custom-built digital speckle pattern shearing interferometer from Oakland University to further this research.
- A new five-year proposal has been approved to continue research on the use of acoustics to improve production in aquaculture settings. The new work will mainly focus on injecting acoustic signals in ponds to move the fish away from seine nets to improve harvesting efficiency. Other aspects of the research will look into the use of ultrasound to control algal blooms and other pathogens in ponds and passively monitor small fish or shrimp to identify mass mortality early enough to allow time to restock. The ultrasound work might also prove useful for improved vaccine delivery.
- Work in collaboration with the University of Arkansas at Pine Bluff also continued on an individual fish-sizer which can provide the size distribution of a sample of captured fish. After a small sub-sample of fish has been captured, they are acoustically scanned as they return to the pond through a restrictive pipe. Measurements were taken in the fall of 2008 and 2009 and the summer of 2010. Continued data analysis is underway.
- DSP based units to monitor sand sized sediments (100-1000 microns) have been delivered to the USDA Agricultural Research Service and another has been delivered to the Bureau of Reclamation. The use of higher frequency (20 MHz) acoustic signals to investigate fines (particles less than 100 microns) continues to produce exceptional results. A fielded system may be available in the near term.
- In allied work on aquaculture, a prototype portable passive monitoring system was assembled and delivered to a commercial shrimp farmer for evaluation of shrimp noise. This passive system has sensitivities comparable to more delicate laboratory grade systems and may be useful for field measurements of gravel motion as these sounds may be louder than sand. Fabrication of potential broad band transducers to support multi-frequency sediment monitoring is also underway with testing slated for the summer and fall of 2010.
- NCPA completed a study for Toyota Central Research and Development Laboratories on acoustic methods to detect oncoming obscured pedestrians and vehicles at intersections
- NCPA scientists and staff have worked with Fibre Craft in Tupelo MS to investigate the potential noise control applications of their recycled fibrous material. A new possible use of their material as a large hemispherical wind screen for the infrasound group is being investigated. A proposal was submitted to the EPA SBIR program for continued research.
- NCPA scientists and staff have continued to investigate the use of accelerometers and lasers to non-destructively determine termite infestations to reduce the need for unnecessary pesticide application. The group has undergone significant personnel changes and a new Post Doc has been hired to help with the research.