Electromagnetic Measurements of Multi-Year Sea Ice Using Impulse Radar

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...

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Bibliographic Details
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
Description
Summary: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.

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