Detailed aeromagnetic survey grid of the Trinidad Area, California

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Frequently anticipated questions:

What does this data set describe?

Title:
Detailed aeromagnetic survey grid of the Trinidad Area, California
Abstract:
This data release provides access to gridded data from a low-altitude, aeromagnetic survey of a part of northwestern California. The survey extends west of the Klamath Mountains across the Pacific Ocean coastline over the continental shelf and covers the towns of Crescent City, Trinidad, Fortuna, Eureka, Arcata, and McKinleyville. Data were acquired during the summer and fall of 2024 by Xcalibur Multiphysics working under contract to the Yurok Tribe and under supervision of the U.S. Geological Survey. Total magnetic field values were acquired using a fixed-wing aircraft flown at a target elevation of 305 meters (m) above terrain and along flight lines and tie lines spaced 600 m and 6000 m apart, respectively. Flight lines were directed northeast-southwest; tie lines were directed northwest-southeast. A total of 13,134 line-kilometers were acquired.
Supplemental_Information:
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  1. How might this data set be cited?
    Watt, Janet T., Langenheim, Victoria E., and Staisch, Lydia M., 20250403, Detailed aeromagnetic survey grid of the Trinidad Area, California: data release DOI:10.5066/P13SZBH7, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

    This is part of the following larger work.

    Watt, Janet T., Langenheim, Victoria E., and Staisch, Lydia M., 2025, Detailed Aeromagnetic Survey of the Trinidad Area, California: data release DOI:10.5066/P13SZBH7, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

    Other_Citation_Details:
    Suggested Citation: Watt, J.T., Langenheim, V.E., and Staisch, L.M., 2025, Detailed aeromagnetic survey of the Trinidad Area, California: U.S. Geological Survey data release, https://doi.org/10.5066/P13SZBH7.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -124.5260
    East_Bounding_Coordinate: -123.7210
    North_Bounding_Coordinate: 41.9360
    South_Bounding_Coordinate: 40.5660
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 28-Aug-2024
    Ending_Date: 27-Sep-2024
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: raster digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Raster data set. It contains the following raster data types:
      • Dimensions 1266 x 576, type Grid Cell
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 10N
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.99960000
      Longitude_of_Central_Meridian: -123.00000000
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.0001
      Ordinates (y-coordinates) are specified to the nearest 0.0001
      Planar coordinates are specified in Meter
      The horizontal datum used is World Geodetic System 1984.
      The ellipsoid used is World Geodetic System 1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257222101.
      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: World Geodetic System 1984
      Altitude_Resolution: 5.0
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method:
      Explicit elevation coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?
    Trinidad_RMI_Final.tif
    Raster geospatial data file containing gridded residual magnetic intensity values (Source: Producer defined)
    Value
    Residual magnetic intensity value (gridded at 120 m interval, UTM10). Values of -3.4028234663852886e+38 indicate no data. (Source: Producer defined)
    ValueDefinition
    -3.4028234663852886e+38no data value
    Range of values
    Minimum:-410.026
    Maximum:1329.842
    Units:nanotesla
    Entity_and_Attribute_Overview:
    The data in this release are as provided to the USGS by the contractor, Xcalibur Multiphysics. The georeferenced GeoTIFF contained in Trinidad_RMI_Final.zip provides residual magnetic intensity values interpolated to a rectilinear grid. The grid is projected to Universal Transverse Mercator Zone 10N, geodetic datum WGS 84, meters. Grid spacing is 120 m in both x and y directions. Additional information is available in the accompanying document 2400075_YurokTribe_Tech_Report_508.pdf, available in the aeromagnetic survey point dataset from this same data release.
    Entity_and_Attribute_Detail_Citation:
    Airborne survey procedures, quality control, and data processing methods are described in the document 2400075_YurokTribe_Tech_Report_508.pdf, provided by the contractor. Gridded residual magnetic intensity values are presented in a georeferenced tiff (Trinidad_RMI_Final.zip).

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Janet T. Watt
    • Victoria E. Langenheim
    • Lydia M. Staisch
  2. Who also contributed to the data set?
    The Trinidad aeromagnetic survey was conducted by Xcalibur Multiphysics, working under contract with the Yurok Tribe and under supervision of the U.S. Geological Survey. David Miles was project manager and data processing was done by Fabian Linares and Tonia Bojkova. The Yurok Tribe coordinated flight and access permissions.
  3. To whom should users address questions about the data?
    PCMSC Science Data Coordinator
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    2885 Mission Street
    Santa Cruz, CA
    US

    831-427-4747 (voice)
    pcmsc_data@usgs.gov

Why was the data set created?

These data were acquired to support earthquake hazard investigations and geologic mapping of the greater Trinidad area of northwestern California. The primary focus was to map continuity and geometry of faults and folds from the town of Fortuna north to Smith River.

How was the data set created?

  1. From what previous works were the data drawn?
    aeromag (source 1 of 1)
    Watt, Janet T., Langenheim, Victoria E., and Staisch, Lydia M., 2025, Detailed aeromagnetic survey point data of the Trinidad Area, California: U.S. Geological Survey, online.

    Online Links:

    Type_of_Source_Media: online database
    Source_Contribution:
    Database of aeromagnetic point measurements along each flight line and tie line in comma-separated-value (CSV) format, available in this same data release.
  2. How were the data generated, processed, and modified?
    Date: 01-Nov-2024 (process 1 of 3)
    While in the field, the base-station magnetometers located in McKinleyville were monitored for magnetic field variations in excess of contract specifications. In the airborne magnetics, a fourth difference was calculated on the compensated total magnetic field in order to verify noise level and identify and remove discrete spikes. Data were corrected for the lag in time between the onboard GPS system and the tail-mounted magnetometer. Uncompensated and compensated total magnetic field profiles were monitored on a daily basis to assess compensation effectiveness. Readings from the two base stations were used to calculate and remove diurnal variations. Please see contractor report (2400075_YurokTribe_Tech_Report_508.pdf) in the aeromagnetic survey point dataset from this same data release for additional details. Person who carried out this activity:
    Janet T. Watt
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Research Geophysicist
    2885 Mission Street
    Santa Cruz, CA
    US

    831-460-7565 (voice)
    jwatt@usgs.gov
    Date: 01-Nov-2024 (process 2 of 3)
    Flight and tie lines were "levelled" using the statistical distribution of total field differences at each flight-line-tie-line crossing. The goal was to obtain the smoothest possible correction model for each line that minimizes the difference in magnetic field measured at each tie-line-flight-line crossing. Finally, the full International Geomagnetic Reference Field (IGRF, Alken and others, 2021), updated to the date of the survey, was subtracted from the measured, corrected total magnetic intensity, thus providing the residual magnetic intensity. The entire dataset is available in this data release in the file Trinidad_aeromag.csv.
    Date: 11-Mar-2025 (process 3 of 3)
    Residual magnetic intensity values (channel mag_rmi in database) were interpolated to a rectilinear grid using a minimum curvature algorithm (Oasis Montaj, Geosoft). The grid is a UTM Zone 10N projection with a cell spacing of 120 by 120 m. Please see the document 2400075_YurokTribe_Tech_Report_508.pdf, in the Supplemental Files section of the point dataset from this same data release for further information. The residual magnetic intensity grid can be downloaded from this data release as a GeoTIFF contained in the file Trinidad_RMI_Final.zip.
  3. What similar or related data should the user be aware of?
    Alken, P., Thébault, E., Beggan, C.D., Amit, H., Aubert, J., Baerenzung, J., Bondar, T.N., Brown, W.J., Califf, S., Chambodut, A., Chulliat, A., Cox, G.A., Finlay, C.C., Fournier, A., Gillet, N., Grayver, A., Hammer, M.D., Holschneider, M., Huder, L., Hulot, G., Jager, T., Kloss, C., Korte, M., Kuang, W., Kuvshinov, A., Langlais, B., Léger, J.-M., Lesur, V., Livermore, P.W., Lowes, F.J., Macmillan, S., Magnes, W., Mandea, M., Marsal, S., Matzka, J., Metman, M.C., Minami, T., Morschhauser, A., Mound, J.E., Nair, M., Nakano, S., Olsen, N., Pavón-Carrasco, F.J., Petrov, V.G., Ropp, G., Rother, M., Sabaka, T.J., Sanchez, S., Saturnino, D., Schnepf, N.R., Shen, X., Stolle, C., Tangborn, A., Tøffner-Clausen, L., Toh, H., Torta, J.M., Varner, J., Vervelidou, F., Vigneron, P., Wardinski, I., Wicht, J., Woods, A., Yang, Y., Zeren, Z., and Zhou, B., 2021, International Geomagnetic Reference Field: the thirteenth generation.

    Online Links:

    Other_Citation_Details:
    Alken, P., Thébault, E., Beggan, C. D., Amit, H., Aubert, J., Baerenzung, J., Bondar, T. N., Brown, W. J., Califf, S., Chambodut, A., Chulliat, A., Cox, G. A., Finlay, C. C., Fournier, A., Gillet, N., Grayver, A., Hammer, M. D., Holschneider, M., Huder, L., Hulot, G., Jager, T., Kloss, C., Korte, M., Kuang, W., Kuvshinov, A., Langlais, B., Léger, J.-M., Lesur, V., Livermore, P. W., Lowes, F. J., Macmillan, S., Magnes, W., Mandea, M., Marsal, S., Matzka, J., Metman, M. C., Minami, T., Morschhauser, A., Mound, J. E., Nair, M., Nakano, S., Olsen, N., Pavón-Carrasco, F. J., Petrov, V. G., Ropp, G., Rother, M., Sabaka, T. J., Sanchez, S., Saturnino, D., Schnepf, N. R., Shen, X., Stolle, C., Tangborn, A., Tøffner-Clausen, L., Toh, H., Torta, J. M., Varner, J., Vervelidou, F., Vigneron, P., Wardinski, I., Wicht, J., Woods, A., Yang, Y., Zeren, Z., and Zhou, B., 2021, International Geomagnetic Reference Field: the thirteenth generation: Earth, Planets and Space, v. 73, n. 49, https://doi.org/10.1186/s40623-020-01288-x

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    Magnetic field values were measured with a Scintrex CS-3 cesium-vapor magnetometer, with a resolution of 0.002 nanotesla (nT). Total magnetic field values were measured at 0.05-sec intervals. Magnetic signals caused by aircraft motion and heading were compensated using a Billingsley TMF 100 Triaxial (X,Y,Z) fluxgate magnetometer mounted in the tail stinger. Prior to the survey, the aircraft and its instrumentation were put through a series of roll, pitch, and yaw maneuvers to form a model of the aircraft's magnetic characteristics. These maneuvers were performed in a region of low magnetic gradient and high altitude to minimize influence of magnetic geologic sources and to develop a compensation correction for the survey data. Two stationary magnetometers were deployed within the survey area at McKinleyville to monitor and subsequently correct for diurnal magnetic field and magnetic storm variations. The base magnetometers were GEM Systems magnetometers sampled at 1-sec intervals. Navigation was accomplished with a GPS system mounted on the tail of the aircraft. The NovAtel Model OEMV-2 receiver has a real-time accuracy of 1.5 meters (L1), sampled at 0.5-sec intervals.
  2. How accurate are the geographic locations?
    Three-dimensional positions were determined with ta NovAtel OEMV-2 receiver with an antenna mounted on the tail of the aircraft. Realtime accuracy is estimated to be 1.5 m.
  3. How accurate are the heights or depths?
    Altitude was determined with the same GPS systems and a Bendix King KRA 10 radar altimeter. Altitude accuracy is estimated to be within 2 to 3 m.
  4. Where are the gaps in the data? What is missing?
    This data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.
  5. How consistent are the relationships among the observations, including topology?
    This dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints No access constraints. Please see 'Distribution Info' for details.
Use_Constraints 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. Users are advised to read the data set's metadata thoroughly to understand appropriate use and data limitations.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - CMGDS
    2885 Mission Street
    Santa Cruz, CA

    831-427-4747 (voice)
    pcmsc_data@usgs.gov
  2. What's the catalog number I need to order this data set?
  3. What legal disclaimers am I supposed to read?
    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.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: .zip file contains the residual magnetic intensity values in format GeoTIFF (version Oasis Montaj, Geosoft, 2024.1) Features are GeoTIFF and are projected in UTM Zone 10N. Size: 2.5
      Network links: https://doi.org/10.5066/P13SZBH7
    • Cost to order the data: None

  5. What hardware or software do I need in order to use the data set?
    These data can be viewed with image viewing or spatial analysis software.

Who wrote the metadata?

Dates:
Last modified: 03-Apr-2025
Metadata author:
PCMSC Science Data Coordinator
U.S. Geological Survey, Pacific Coastal and Marine Science Center
2885 Mission Street
Santa Cruz, CA
US

831-427-4747 (voice)
pcmsc_data@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/pcmsc/DataReleases/CMGDS_DR_tool/DR_P13SZBH7/Trinidad_RMI_Final_metadata.faq.html>
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