Details: The
Cassiar map features an airborne aeromagnetic survey, conducted in 1995 and
1996. The files are also available for download
in georeferenced PNG format.
View
Cassiar Geophysics Map
Survey Background
CASSIAR GEOPHYSICAL SURVEY
Open File GSC 3198
1997 Aeromagnetic Total Field Map, British Columbia
(Parts of NTS 104P/NW)
The aeromagnetic survey was carried out by Geoterrex
using a Titan 404 aircraft. A 0.005 nT sensitivity
split-beam cesium vapour magnetometer was mounted in the tail boom of
the survey aircraft.
The survey operations were carried out
from August, 1995 to March, 1996. Sensor height was a smooth drape, to
within 300 metres of the highest peaks; it was controlled by a computer
assisted, real-time corrected Global Positioning System, which provided
vertical, as well as horizontal guidance. This vertical guidance ensured
correlation of elevation of traverse and control line intersections. The
average traverse line spacing was 800 meters with control lines at 5
kilometre spacing.
Flight path was recovered using a post flight differential Global
Positioning System, combined with a vertically mounted video camera.
After editing the survey data, the
intersections of control and traverse lines were established and the
differences in the magnetic values were computer analyzed and manually
checked to obtain the level network. Because short-period diurnal
micropulsations will pass through standard control line levelling, a
micro-levelling operation (Minty, B.R.S., 1991: Exploration Geophysics, 22,
591-592) was applied to the total field grid. Intensive manual intervention
with the micro-levelling corrections prevented any significant alteration of
real magnetic signal. Turbulence-induced altitude variations were examined
by computer for correlative wavelengths in the magnetic data. Corrections of
up to 0.022 nT/m were applied at correlative sites. The levelled total field
values were then interpolated to a 100 m grid. The International Geomagnetic
Reference Field has not been removed. The data were processed by Geoterrex.
Copies of this map may be obtained from
the Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8.
It is also available online at the
MIRAGE and at the
Geoscience Data Repository. The geophysical data used to compile this map are available in digital form
from the Geophysical Data Centre. Geological Survey of Canada, 1 Observatory
Crescent, Ottawa. Ontario, K1A 0Y3.
Analogue and digital products
include data for magnetic parameters in two projections:
