Electromagnetic Measurements of Multi-Year Sea Ice Using Impulse Radar

• Main Authors: Kovacs,A., Morey,R. M.
• Other Authors: COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
• Format: Text
• Language: English
• Published: 1985
• Subjects: Snow; Ice and Permafrost; Active & Passive Radar Detection & Equipment; Electricity and Magnetism; *ELECTROMAGNETIC PROPERTIES; *RADAR; *DIELECTRIC PROPERTIES; *SEA ICE; MEASUREMENT; THICKNESS; VOLUME; HIGH RATE; STRUCTURAL PROPERTIES; FORMULATIONS; DIELECTRICS; COLD REGIONS; TARGETS; BULK MATERIALS; GASES; ICE; PULSES; ELECTROMAGNETIC RADIATION; CONSTANTS; MIXING; LOSSES; BOTTOM; SUBSURFACE; TWO PHASE FLOW; ROCKETS; BRINES; MARINE GEOPHYSICS; Ice; permafrost; Sea ice
• Online Access: http://www.dtic.mil/docs/citations/ADA160737; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA160737

Sounding of multi-year sea ice, using impulse radar operating in the 80- to 500-MHz frequency band, has revealed that the bottom of this ice cannot always be detected. This paper discusses a field program aimed at finding out why this is so, and at determining the electromagnetic (EM) properties of multi-year sea ice. It was found that the bottom of the ice could not be detected when the ice structure had a high brine content. Because of brine's high conductivity, brine volume dominates the loss mechanism in first-year sea ice, and the same was found true for multi-year ice. A two-phase dielectric mixing formula, used by the authors to describe the EM properties of first-year sea ice, was modified to include the effects of the gas rockets found in the multi-year sea ice. This three-phase mixture model was found to estimate the EM properties of the multi-year ice studied over the frequency band of interest. The latter values were determined by: (1) verified sounding to a subsurface target of known depth, where the two-way travel time of the EM wavelet in the ice is measured; (2) cross-borehole transmission, where the transit time of the EM wavelet is measured through a known thickness of sea ice; and (3) a wide-angle or common-depth-point reflection method. Preliminary findings also indicate that a representative value for the apparent bulk dielectric constant of multiyear sea ice over 2 1/2 m thick is 3.5. Keywords includ: Cold regions, Electromagnetic properties, Marine geophysics, and Sea ice.