Long Valley Ground Magnetic Data
Processing
DATA PROCESSING STEPS
- Original binary data from the G-858 for each
profile were converted to ASCII data using MagMap 2000 software.
These data contain longitude, latitude, top sensor reading, bottom
sensor reading, vertical gradient, time, and date. The data were
filtered in MagMap 2000 by removing all dropout values, which could
have been the result of the instrument being in a dead zone or near a
large iron or steel object.
- Original binary data from the G-856 for
each
day
were converted to ASCII data using MagMap 2000 software. These
data contain date, time, and sensor reading. The base
magnetometer
data were filtered by removing dropouts, despiking fluctuations, and
smoothing the resultant values to a curve using a third degree spline
filter.
- A diurnal correction was performed using
the
MagMap 2000 software, and the resultant data was exported using the
ASCII Geosoft
.xyz format into file "long_valley.XYZ".
- The data files were merged into one
database
("long_valley.gdb") using Geosoft’s OASIS montaj.
- Profiles of top sensor, bottom sensor,
vertical
gradient, and the two diurnally corrected channels were plotted, and
the
remaining data spikes were then deleted. Subsequently, a linear
interpolation was performed on the top sensor, bottom sensor, and the
two diurnally corrected channels to fill in the deleted values.
The vertical gradient channel was then recalculated.
- The
final data set contains fifteen channels:
- long – Longitude in WGS84
- lat – Latitude in WGS84
- X_UTM – UTM zone 11N, NAD83
- Y_UTM – UTM zone 11N, NAD83
- elevation – Elevation in meters
- TOP_RDG_RAW – Raw magnetic value of top sensor
(nT)
- TOP_RDG – Despiked magnetic value of top sensor
(nT)
- TOP_DNL – Diurnal correction for top sensor
using processed base station values (nT)
- BOTTOM_RDG_RAW – Raw magnetic value of bottom
sensor (nT)
- BOTTOM_RDG – Despiked magnetic value of bottom
sensor (nT)
- BOTTOM_DNL – Diurnal correction for bottom
sensor using processed base station values (nT)
- VRT_GRAD – TOP_RDG minus BOTTOM_RDG (nT)
- base_mag – Base station magnetic value after
removing dropouts, despiking, and applying third degree spline filter
(nT)
- TIME – GPS time the reading was taken
- DATE – Date the reading was taken
REFERENCES
Roberts, C. W. and Jachens, R. C., 1999, Preliminary
aeromagnetic anomaly map of California: U.S. Geological Survey
Open-File Report 99-440, scale 1:250,000.
Sorey, M. L., McConnell, V. S., and Roeloffs, E., 2003,
Summary of recent research in Long Valley Caldera, California: Journal
of Volcanology and Geothermal Research, v. 127 pp. 165 – 173.
Stroujkova, A. F and Malin, P. E., 2000, A magma
mass beneath Casa Diable? Further evidence from reflected seismic
waves: Bulletin of the Seismological Society of America, v. 90, no. 2
pp. 500 – 511.
Willams, D. L., Berkman, F., and Mankinen, E. A.,
1977, Implications of a magnetic model of the Long Valley Caldera,
California: Journal of Geophysical Research, v. 82, no. 20, pp. 3030 – 3038.
Download data
Top
|| CICT
|| Minerals
