The effective ground conductivity of Alaska has been determined by a
comparison of experimental and theoretical field strengths. The experimental
field strengths have been obtained by use of an airborne receiver, flown along
radial paths from a large number of CAA radio ranges and beacons. The surface
wave attenuation factor was computed for both a plane and a curved, homogeneous
earth by methods presented by Norton. The experimentally determined relative
field strengths were plotted as a function of distance and were compared with
a family of curves for assumed values of conductivity and dielectric constant.
From this comparison, that value of conductivity that best fits the experimental
data is taken as the effective conductivity over the path.
An investigation of the effect at dielectric constant on the transmitted
signal shows that, within the frequency range used, a change of dielectric
constant from 1 to 20 has but little effect on the attenuation of the transmitted
signal for values of conductivity between 1 and 5 mmho/m. The experimental
results indicate that for most sections of Alaska, the effective conductivity
falls within this range.
In some cases the earth was not homogeneous over the entire flight path
as evidenced by changes in the slope of the field strength vs distance curves.
In such cases, the data were replotted with an initial point at the discontinuity
and new theoretical curves were drawn for each section of the field strength
vs distance curves.
Investigation of the variation of effective conductivity with change of
frequency and at different seasons was made.
In addition, wave tilt methods of determining the conductivity were used.
A 'Ground Constants Measuring Set' was obtained from the Signal Corps and
measurements were made in selected areas in Alaska.
Attempts were made to use 1height-gain' and 'mutual coupling of loops'
techniques but these were not successful.
An investigation of anomolous propagation in the vicinity of Point Barrow
was made. It was determined that this anomolous propagation appears to be
the result of a layered earth. In addition to the anomolous propagation in
the vicinity of Point Barrow, there appears to be similar anomolies in the
vicinity of Kotzebue, Galena, Bethel and Port Heiden.
From the above investigations a map showing the effective conductivity of
Alaska as determined by the attenuation method is presented.Navy Department Bureau of Ships
NObsr 72528 NE 120308 Subtask No. 6ABSTRACT -- PART I
A. Purpose --
B. General Factual Data --
C. Detail Factual Data --
PART II --
A, Conclusions --
APPENDIX IYe