Magnetic fields of AM band radio broadcast signals at theRichmond Fiel d Station
Non-invasive sensing of the shallow subsurface is necessary for detection and delineation of buried hazardous wastes, monitoring of the condition of clay containment caps, and a variety of other purposes. Electromagnetic methods have proven to be effective in environmental site characterization where there is a need for increased resolution in subsurface characterization. Two considerations strongly suggest the use of frequencies between 100 kHz and 100 MHz for such applications: 1) the induction response of many targets is small due to small size, and 2) a need to determine both the electrical conductivity and dielectric permittivity which are related to chemistry and hydrology. Modeling and physical parameter studies confirm that measurements at frequencies between 1 and 100 MHz can resolve variations in subsurface conductivity and permittivity. To provide the necessary technology for shallow subsurface investigations, we propose to exploit the concept of electromagnetic impedance, the ratio of orthogonal horizontal electric and magnetic fields. Prior to assembling the equipment for measuring surface impedance using controlled, local source it was felt prudent to measure the surface impedance of geological materials at the University of California at Berkeley's Richmond Field (RFS) using ambient energy in the broadcast band. As a first step toward this intermediate goal, we have examined and characterized local AM band radio signals in terms of both signal strength and polarization of the magnetic component as received at RFS. In addition, we have established the viability of a commercial radio-frequency magnetic sensor.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Environmental Management
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 7363
- Report Number(s):
- LBNL-42654; ON: DE00007363
- Country of Publication:
- United States
- Language:
- English
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