Marine magnetic data from Point Sur to Piedras Blancas, central California, 2011
This dataset includes marine magnetic data collected by the U.S. Geological Survey (USGS) in 2011 during field activity B-05-11-CC between Point Sur and Piedras Blancas, central California.
Additional information about the field activity from which these data were derived is available online at:
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Watt, Janet T., Hartwell, Stephen R., and Johnson, Samuel Y., 2018, Marine magnetic data from Point Sur to Piedras Blancas, central California, 2011: data release DOI:10.5066/F7FB51F7, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA.
What coordinate system is used to represent geographic features?
Horizontal positions are specified in geographic coordinates, that is, latitude and longitude.
Latitudes are given to the nearest 0.00001.
Longitudes are given to the nearest 0.00001.
Latitude and longitude values are specified in Decimal degrees.
The horizontal datum used is North American Datum of 1983.
The ellipsoid used is Geodetic Reference System 80.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.257.
Magnetic data were postprocessed following the methodology:
1)Initial Processing in MagMap2000
-Download base files from INTERMAGNET observatory (http://www.intermagnet.org/apps/dl_data_prel_e.php)
-Despike base files and visually inspect for dropouts
-Apply bias to DIURNAL (base) readings for GMT to local PDT + longitude diff. from base to survey = 7hrs + 0.22hrs =-24,408sec **NOTE: 0.0666667hr/deg longitude correction
-Import .survey files, despike
2)Import to Oasis
-Remove periodic sparker spike from raw G882 and G882_diurnal channel using a non-linear filter GX = nlfilt
(ex. filter width = 3 data points, filter tolerance = 0.3 nt)
3)Calculated IGRF for G882 data
4)Back calculated Base Magnetometer measurements
G882filt-DIURNAL_filt = Fresno_base
5)Calculated IGRF value at base station FRN = 48909.6nT
6)Calculated Total Field (Residual) Anomaly using the following equation:
A(x) = [F(x,t) - I(x)] - [FB(t) - IB]
A(x)is total field anomaly at position x
F(x,t) is the G882 reading at time t and position x
I(x) is IGRF/DGRF at the G882
FB(t) is the base station reading at time t
IB is the IGRF/DGRF at the base station
7)Performed tie line leveling
8) Manually edited a subset of lines (+6 nT)
9) Applied a decorrugation filter "L" lines only (500m line spacing, line azimuth=30 degrees)
Following methodology at Geosoft - http://www.geosoft.com/media/uploads/resources/technical-notes/microleveling%20tech%20note.pdf
FILTER PARAMETERS for "L" lines
cutoff wavelength = 2000 (4 x line spacing)
filter order = 8 (suggested)
Directional Cosine filter:
centre direction = 30 (shiptrack azimuth)
degree of cosine function = 0.5 (suggested)
Date: 19-Oct-2020 (process 2 of 2)
Edited metadata to add keywords section with USGS persistent identifier as theme keyword. No data were changed.
Person who carried out this activity:
USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data.
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What's the catalog number I need to order this data set?Downloadable magnetic field data These data are available in shapefile format (PointSurToPiedrasBlancas_magnetics.shp and associated files) contained in a single zip file (PointSurToPiedrasBlancas_magnetics.zip), which also include CSDGM FGDC-compliant metadata.
Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty.