Metadata: Identification_Information: Citation: Citation_Information: Originator: Philip J. Brown II Publication_Date: 2006 Title: Aeromagnetic Survey of Dillingham Area in Southwest Alaska, A Website for the Preliminary Distribution of Data Geospatial_Data_Presentation_Form: remote-sensing image, ASCII text Series_Information: Series_Name: U.S. Geological Survey Data Series Issue_Identification: 2006-1136 Publication_Information: Publication_Place: Denver, CO Publisher: U.S. Geological Survey Online_Linkage: http://pubs.er.usgs.gov/usgspubs/ofr/ofr061136 Description: Abstract: Aeromagnetic data from the Dillingham, Nushagak Bay and Naknek Quadrangle areas in South West Alaska. Purpose: Presentation of aeromagnetic data values for use in geological and geophysical studies. Supplemental_Information: This file defines the data being released and data used to create the map plate (72 dpi) of the gridded data presented in PDF format on the website. These data are position located in Latitude and Longitude using the North American Datum 1927 (NAD27) datum and in X and Y using the NAD27 datum and Universal Transverse Mercator (UTM) 4 North projection. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 2005 Ending_Date: 2005 Currentness_Reference: ground condition Status: Progress: Complete Maintenance_and_Update_Frequency: None planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -159:15 East_Bounding_Coordinate: -155:45 North_Bounding_Coordinate: 60:06 South_Bounding_Coordinate: 58:30 Keywords: Theme: Theme_Keyword_Thesaurus: None Theme_Keyword: Geophysical data Theme_Keyword: Aeromagnetic data Place: Place_Keyword_Thesaurus: None Place_Keyword: Alaska Place_Keyword: Dillingham Quadrangle Place_Keyword: Nushagak Quadrangle Place_Keyword: Naknek Quadrangle Access_Constraints: None Use_Constraints: None Point_of_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Philip J. Brown II Contact_Organization: U.S. Geological Survey Contact_Address: Address_Type: mailing address Address: USGS, Box 25046, Mail Stop 964 Denver Federal Center City: Denver State_or_Province: CO Postal_Code: 80225-0046 Country: USA Contact_Voice_Telephone: (303) 236-1310 Contact_Electronic_Mail_Address: pbrown@usgs.gov Browse_Graphic: Browse_Graphic_File_Name: http://pubs.er.usgs.gov/usgspubs/ofr/ofr061136/images/DillinghamMagMapPlate.pdf Browse_Graphic_File_Description: Image of the entire survey grid grid, 2592x2088 pixels, 2,087 Kbytes. Browse_Graphic_File_Type: PDF Data_Set_Credit: Data were collected in 2004 by a private contractor under contract to the U.S. Geological Survey. Native_Data_Set_Environment: At the USGS, these data are stored in binary and ASCII data format on CD ROM. Data and maps have been distributed in ASCII and PDF format, respectively. Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: Map values represent the total intensity of the Earth's magnetic field after removal of the International Geomagnetic Reference Field (IGRF). Measurements were made by a variety of magnetometer systems with typical accuracy of 1 to 10 nanotesla (nT). In addition to corrections for the IGRF, the data typically contain corrections for the diurnal variations of the Earth's magnetic field that occurred during the flight (as recorded by a base station magnetometer) and leveling adjustments made at flightline intersections. The absolute accuracy of the gridded data are probably better than 5 nanotesla, with accuracy increasing with increasing wavelength. Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: Horizontal position of the aircraft were determined by a differential Global Positioning System (GPS)to a precision of approximately 1.5 m. Quantitative_Horizontal_Positional_Accuracy_Assessment: Horizontal_Positional_Accuracy_Value: 1.5 Horizontal_Positional_Accuracy_Explanation: meters Vertical_Positional_Accuracy: Vertical_Positional_Accuracy_Report: Vertical position of the aircraft were determined by a differential Global Positioning System (GPS)to a precision of approximately 1.5 m. Quantitative_Vertical_Positional_Accuracy_Assessment: Vertical_Positional_Accuracy_Value: 1.5 Vertical_Positional_Accuracy_Explanation: meters Lineage: Process_Step: Process_Description: Processing of aeromagnetic data. Daily quality control, initial processing and archiving of the data were done on-site at the base of operations in Dillingham, Alaska. The final data processing, map generation and report writing were undertaken at the offices of McPhar Geosurveys Ltd. in Newmarket, Ontario, Canada. The flight path was derived from differentially corrected GPS positions using the airborne and static GPS data. Differential GPS data editing and processing was accomplished using the GrafNav GPS processing system as developed by WayPoint Navigation, Inc. A position was calculated each 1.0 second (approximately each 60 meters along the flight path) to an accuracy of better than ñ1.5 meter. These position data were merged into magnetic and ancillary data in the Geosoft GDB database. The magnetometer data were edited, plotted and merged into the GDB database on a daily basis. In order to obtain values of the measured Horizontal Gradient in nanotesla/meter, values recorded by the two wing tip magnetometers were subtracted (after applying all necessary corrections), always in the same direction, and the result was divided by the distance between the sensors (12.9 m). The processing of the Naknek, Nushagak, and Dillingham data involved post- flight compensation for the movement and orientation of the aircraft in the Earth's magnetic field. This corrected dataset was used to generate the initial grids and served as a base for all further processing and analysis. After reviewing the base mag corrected profiles and grids, a decision was made to apply the base station correction to the tie lines only, and further deal with the removal of diurnal variations from the traverse line data by applying the tie line leveling procedure. After applying the above-mentioned initial corrections to the profile data there were still some line-direction-related noise present on the calculated grids. To remove this noise, microleveling was applied. Its main purpose is to remove from the data remaining line direction-related noise. The microleveling technique consists of applying directional and high-pass filters to the resulting grid, which leaves signal with noise-only in the line direction. In order to differentiate between the two of them, the grid is extracted to the profile database, and an amplitude limit and a filter length are determined, so that the final error channel reflects only noise present on the grid without removing or changing geological signal. This error channel is then subtracted from the initial data channel in order to get the final microleveled channel. The resulting grid is then free of line-direction-related noise. This method was applied to the Total Magnetic Field and Digital Elevation Model Channels. These channels were then subjected to further gridding and spatial filtering. Process_Date: 2006 Process_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Patricia L. Hill Contact_Organization: U.S. Geological Survey Contact_Address: Address: USGS Mail Stop 964 City: Denver State_or_Province: CO Postal_Code: 80225-0046 Country: USA Address_Type: mailing address Contact_Electronic_Mail_Address: pathill@usgs.gov Contact_Voice_Telephone: (303) 236-1343 Logical_Consistency_Report: The flight data collected to generate the final product is dependent on the contractor. All corresponding corrections were then made by the contractor and a final data set was presented for gridding. Compositing of the individual surveys was done in an analog process before digitizing. The process of reprojecting the grid does not affect the accuracy of the product. Completeness_Report: All data and information supplied by the contractor were included in the preperation of this USGS data series report. Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: Raster Raster_Object_Information: Raster_Object_Type: PDF file Row_Count: 2592 Column_Count: 2088 Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Grid_Coordinate_System: Grid_Coordinate_System_Name: Universal Transverse Mercator Universal_Transverse_Mercator: UTM_Zone_Number: 4 Transverse_Mercator: Scale_Factor_at_Central_Meridian: 0.999600 Longitude_of_Central_Meridian: -159.000000 Latitude_of_Projection_Origin: 0.000000 False_Easting: 500000.000000 False_Northing: 0.000000 Planar_Coordinate_Information: Planar_Coordinate_Encoding_Method: coordinate pair Coordinate_Representation: Abscissa_Resolution: 0.000004 Ordinate_Resolution: 0.000004 Planar_Distance_Units: meters Geodetic_Model: Horizontal_Datum_Name: NAD27 Ellipsoid_Name: Clarke 1866 Semi-major_Axis: 6378206.4 Denominator_of_Flattening_Ratio: 294.98 Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Label: Grid cell Entity_Type_Definition: Area of the earth's surface represented by an observation Attribute: Attribute_Label: Residual total intensity of Earth's magnetic field Attribute_Definition: Value, in nanotesla, of total intensity of Earth's magnetic field after removal of the theoretical International Geomagnetic Reference Field value. Attribute_Definition_Source: Paterson, N.R., and Reeves, C.V., 1985, Applications of gravity and magnetic surveys: The state-of-the-art in 1985: Geophysics, v. 50, p. 2558-2594. Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -10,000 Range_Domain_Maximum: 10,000 Attribute_Units_of_Measure: nanotesla Attribute_Measurement_Resolution: 1-10 nanotesla Attribute_Domain_Values: Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: Areas outside the irregular survey boundary Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 5.0 Attribute_Value_Accuracy_Explanation: nanotesla Distribution_Information: Distributor: Contact_Information: Contact_Person_Primary: Contact_Person: Philip J. Brown II Contact_Organization: U.S. Geological Survey Contact_Electronic_Mail_Address: pbrown@usgs.gov Contact_Address: Address_Type: mailing address Address: Box 25046, MS 964 Denver Federal Center City: Denver State_or_Province: CO Postal_Code: 80225 Country: USA Contact_Voice_Telephone: (303) 236-1310 Resource_Description: USGS Data Series Report 2006-1136 Distribution_Liability: The USGS has made every effort to verify the veracity of this information, but is not liable for any inaccuracies. Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: Geosoft Oasis montaj XYZ export Format_Version_Number: 6.x Format_Information_Content: Data are presented in ASCII text format. Header information for the ASCII white space delimited columns are as follows: Column Header Column Description ============= ================== Line Line number GHead_deg Flight Line direction in degree from North Lon_NAD27 Longitude, NAD-27 Lat_NAD27 Latitude, NAD-27 x_NAD27 UTM 4N X (meters), NAD-27 y_NAD27 UTM 4N Y (meters), NAD-27 RECS_ Fiducial date Year and Julian date time Time of date (UTC) Galt_m GPS Height (meters) Raltmf Height above ground (radar altimeter) (meters) Baro_m Barometric altitude (meters) var_dil Diurnal collected on base station in Dillingham-offset 53909.08 nT var_kol Diurnal collected on base station in Koliganak-offset 54090.17 nT mag Raw compensated TMI (nT) magvd TMI corrected for diurnal (Dillingham) (nT) mgvdl12 TMI corrected for diurnal (Dillingham) and lag (1.2s) (nT) maglev TMI -after conventional leveling applied (nT) IGRF IGRF - model 2000 (nT) Maglev_IGRF TMI leveled - IGRF removed (nT) TMI_IGRF Micro leveled TMI File_Decompression_Technique: zip Transfer_Size: 106,359 KB Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: http://pubs.er.usgs.gov/usgspubs/ofr/ofr061136/data/DillinghamAreaMag.zip Network_Resource_Name: http://pubs.er.usgs.gov/usgspubs/ofr/ofr061136/data/DillinghamMag.XYZ Network_Resource_Name: http://pubs.er.usgs.gov/usgspubs/ofr/ofr061136/data/DillinhamMagDatabaseHeaderDescription.txt Network_Resource_Name: http://pubs.er.usgs.gov/usgspubs/ofr/ofr061136/data/USGS_DillinghamAreaMagFinalReport.pdf Fees: none Metadata_Reference_Information: Metadata_Date: 20060320 Metadata_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Philip J. Brown II Contact_Organization: U.S. Geological Survey Contact_Electronic_Mail_Address: pbrown@usgs.gov Contact_Address: Address_Type: mailing address Address: Box 25046, MS 964 Denver Federal Center City: Denver State_or_Province: Co Postal_Code: 80225 Country: USA Contact_Voice_Telephone: (303) 236-1310 Metadata_Standard_Name: Content Standard for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998