Accession Number : AD0718438

Title :   Evaluation of Airborne Electromagnetic Surveying for Mapping Variations in Rock Strength.

Descriptive Note : Final rept. 1 Mar 69-1 Jul 70,

Corporate Author : COLORADO SCHOOL OF MINES GOLDEN DEPT OF GEOPHYSICS

Personal Author(s) : Keller,George V. ; Lebel,Andre B. ; Ausman,Evan L. , Jr

Report Date : 01 DEC 1970

Pagination or Media Count : 70

Abstract : The objective of the report is to determine the feasibility of estimating variations in ground strength on the basis of electrical conductivities measured from the air. A review of the literature indicates that for a wide variety of crystalline igneous rocks, a reasonably unique relationship should exist between resistivity and strength. Three airborne electromagnetic surveying techniques hold promise for measuring ground conductivity in the desired range. These are, in order of the ease with which surveys might be made with existing or modified systems, the wave-tilt method, the long-grounded-wire method and the INPUT method. The wave-tilt method makes use of waves radiated by VLF broadcast stations in the frequency range from 15 to 30 KHz, and is useful with no modification of commercially available equipment, as field tests described in this report indicate. The long-grounded-wire method makes use of fields from a current-carrying cable installed specifically for a survey. The INPUT method makes use of a transmitter carried on the aircraft with the receiver. However, in order to measure conductivities in the range of interest with the existing commercial INPUT system, major modifications would be required. (Author)

Descriptors :   (*ELECTRICAL CONDUCTIVITY, MAPPING), (*AERIAL RECONNAISSANCE, ELECTROMAGNETIC FIELDS), (*ROCK, STRUCTURAL PROPERTIES), (*UNDERGROUND STRUCTURES, CONSTRUCTION), FEASIBILITY STUDIES, ELECTRICAL RESISTANCE, AIRBORNE, MAGNETOMETERS

Subject Categories : Geology, Geochemistry and Mineralogy

Distribution Statement : APPROVED FOR PUBLIC RELEASE