l275np.m77t - MGD77 data file for Geophysical data from feld activity L-2-75-NP in Gulf of Alaska from 08/25/1975 to 09/04/1975

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Frequently anticipated questions:


What does this data set describe?

Title:
l275np.m77t - MGD77 data file for Geophysical data from feld activity L-2-75-NP in Gulf of Alaska from 08/25/1975 to 09/04/1975
Abstract:
Single-beam bathymetry and magnetics data along with DGPS navigation data was collected as part of field activity L-2-75-NP in Gulf of Alaska from 08/25/1975 to 09/04/1975, http://walrus.wr.usgs.gov/infobank/l/l275np/html/l-2-75-np.meta.html These data are reformatted from space-delimited ASCII text files located in the Coastal and Marine Geology Program (CMGP) InfoBank field activity catalog at http://walrus.wr.usgs.gov/infobank/l/l275np/html/l-2-75-np.bath.html and http://walrus.wr.usgs.gov/infobank/l/l275np/html/l-2-75-np.mag.html into MGD77T format provided by the NOAA's National Geophysical Data Center(NGDC). The MGD77T format includes a header (documentation) file (.h77t) and a data file (.m77t). More information regarding this format can be found in the publication listed in the Cross_reference section of this metadata file.
Supplemental_Information:
The navigation data are digitally collected using a Satellite Integrated Navigation (SINS) system. The system is a space-based satellite navigation maintained by the United States government and is accessible using a satellite receiver. This system provides navigational accuracy of approximately 200 m.The Data Acquistion, Processing, and Storage (DAPS) group performs a number of processing steps to the navigation data once it is collected which can vary by cruise. These steps are outlined within the header information in each individual digital navigation (.05x) space-delimited ASCII data file. The header information rows are indicated by lines beginning with the character "!". There is no information on how the single-beam bathymetry, gravity, and magnetic data were collected. For each data gathering cruise leg, the available data in the following categories are forwarded to NGDC: navigation, gravity, magnetics, bathymetry, and seismic shot points. The available data for each cruise leg are re-formatted and combined into the Marine Geophysical Data Exchange Format (MGD77) and into the internal NGDC SEIS-NAV format by USGS using several USGS developed FORTRAN programs.The FORTRAN programs sample the navigation to every integer minute of the cruise. When necessary, the latitudes and longitudes are linearly interpolated. If the time between the actual navigation fixes exceeds five minutes, no data are included in the MGD77 file.To build the MGD77 file, gravity, magnetics, and bathymetry are added to this sampled navigation. When necessary, gravity, magnetics, and bathymetry data are linearly interpolated if the time between the actual data samples does not exceed five minutes. If a time gap exceeds this, the data are not reported.The navigation data are merged with the seismic shot point data in a SEIS- NAV format file. For this file, navigation data are interpolated for each shot point. Both types of files are written to magnetic tape and sent to NGDC.
  1. How might this data set be cited?
    U.S. Geological Survey, and Coastal and Marine Geology Program, 2013, l275np.m77t - MGD77 data file for Geophysical data from feld activity L-2-75-NP in Gulf of Alaska from 08/25/1975 to 09/04/1975: U.S. Geological Survey, Menlo Park, CA.

    Online Links:

    This is part of the following larger work.

    Steele, Wm. Clinton, Degnan, Carolyn H., Deeter, Gary B., and Riordan, Jean A., 1980, DESCRIPTION OF MARINE GEOPHYSICAL DATA COLLECTED BY THE U.S. GEOLOGICAL SURVEY AND HOW TO OBTAIN IT: U.S. Geological Survey Open File Report 167, U.S. Geological Survey, Menlo Park, CA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -166.49365
    East_Bounding_Coordinate: -122.66299
    North_Bounding_Coordinate: 54.63333
    South_Bounding_Coordinate: 37.77899
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 25-Aug-1975
    Ending_Date: 04-Sep-1975
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: tab-delimited ASCII text files
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      Indirect_Spatial_Reference: Gulf of Alaska
      This is a Point data set. It contains the following vector data types (SDTS terminology):
      • Point
    2. 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 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.25722210100002.
  7. How does the data set describe geographic features?
    l275np.m77t
    MGD77T single-beam bathymetry data file for L275NP (Source: NOAA's National Geophysical Data Center, See Hittelman and others (2010) Cross_Reference section above for details about the MGD77T format and citation information.)
    SURVEY_ID
    Survey identifier supplied by the contributing organization (Source: NGDC) This identifier varies in format and is supplied by the contributing organization
    TIMEZONE
    Time-zone correction (Source: NGDC) In our datasets, no correction was applied. All values equal 0.
    DATE
    YYYYMMDD (Source: NGDC)
    Range of values
    Minimum:19750825
    Maximum:19750904
    Units:Year, month, day
    TIME
    Time (Source: NGDC)
    Range of values
    Minimum:0
    Maximum:2350
    Units:hours and decimal minutes
    LAT
    Latitude (Source: World Geodetic System 1984 Geographic Coordinate System)
    Range of values
    Minimum:37.77899
    Maximum:54.63333
    Units:decimal degrees
    LON
    Longitude (Source: World Geodetic System 1984 Geographic Coordinate System)
    Range of values
    Minimum:-166.49365
    Maximum:-122.66299
    Units:decimal degrees
    POS_TYPE
    Indicates how lat/lon was obtained (Source: NGDC)
    Range of values
    Minimum:1
    Maximum:3
    Units:1 = observed fix, 3 = interpolated fix, nil = unspecified
    MAG_TOT
    Magnetics total field - 1st sensor (Source: NGDC)
    Range of values
    Minimum:52279.1
    Maximum:59880.1
    Units:gammas
    MAG_RES
    Magnetics residual field field (Source: NGDC)
    Range of values
    Minimum:-182.9
    Maximum:8445.3
    Units:gammas
    Entity_and_Attribute_Overview:
    Bathymetry, magnetics, and navigation data for U.S. Geological Survey bathymetry survey L275NP in MGD77T format.
    Entity_and_Attribute_Detail_Citation:
    Attributes are obtained from MGD77T data files created from the navigation, magnetics, and bathymetry best files. MGD77T is the standard, defined data format used for geophysical data in the National Geophysical Data Center. See Cross_Reference section above for citation details.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Geological Survey
    • Coastal and Marine Geology Program
  2. Who also contributed to the data set?
    Dave Scholl (Chief Scientist)
  3. To whom should users address questions about the data?
    Gregory K. Miller
    U.S. Geological Survey
    Physical Scientist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 803-8747, ext. 3020 (voice)
    gmiller@usgs.gov

Why was the data set created?

These data and information are intended for science researchers,students, policy makers, and general public. These data are not to be used for navigation purposes. The data are reformatted into MGD77T standard format for inclusion into NOAA's NGDC geophysical database. From there the data will be made available to GeoMapApp ( http://www.geomapapp.org/ ) and Virtual Ocean ( http://www.virtualocean.org/ ) Earth-browsing software. Access to the data is also provided via the USGS Coastal and Marine Geoscience Data System ( http://cmgds.marine.usgs.gov/ ).

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 19-Jan-1996 (process 1 of 5)
    Navigation Data >Converted to time format with year at start. > >02/11/86 KAYE DUA0:[DATA.L275NP.N]L275NP.051; >DRB0:[DRS.REFMT]REFORMAT.EXE;5 > Person who carried out this activity:
    U.S. Geological Survey (USGS) , Coastal and Marine Geology (CMG)
    Attn: Carolyn H. Degnan
    Geophysicist
    USGS Pacific Coastal & Marine Science Center, 400 Natural Bridges Drive
    Santa Cruz, CA
    USA

    (831) 460-7452 (voice)
    (831) 427-4748 (FAX)
    infobank@octopus.wr.usgs.gov
    Date: 20-Jun-2012 (process 2 of 5)
    Magnetics Data >06/20/2012 carolyn l-2-75-np.220_051 > >Reprocessed using subroutines from Susan Macmillan's >IGRF SYNTHESIS PROGRAM http://www.ngdc.noaa.gov/IAGA/vmod/igrf11.f >with IGRF-11 coeffiecients integrated into the source code. >/infobank/programs/mag/magred11/magred11.for >Using geodetic coordinate system (Earth shape approximated by spheriod) >with altitude 0.0 km (for sea level). > >Input was... >10/31/1998 /tiger/l/l275np/mag/l-2-75-np.200_051 >/bear/programs/edit/automerge/automerge > >Converted to time format with year at start. > >02/14/86 CAROLYN DRS$DATA:[L275NP.M]L275NP.200; >DRB0:[DRS.REFMT]REFORMAT.EXE;5 >was L275NP._.MAGSX1 on TAM157 >was L275NP201.DAT on VAM157 > >Converted to time format with year at start. > >02/11/86 KAYE DUA0:[DATA.L275NP.N]L275NP.051; >DRB0:[DRS.REFMT]REFORMAT.EXE;5 > >time, lat, long, time(sec) to nearest nav fix, data values Person who carried out this activity:
    U.S. Geological Survey (USGS) , Coastal and Marine Geology (CMG)
    Attn: Carolyn H. Degnan
    Geophysicist
    USGS Pacific Coastal & Marine Science Center, 400 Natural Bridges Drive
    Santa Cruz, CA
    USA

    (831) 460-7452 (voice)
    (831) 427-4748 (FAX)
    infobank@octopus.wr.usgs.gov
    Date: 31-Oct-1998 (process 3 of 5)
    Bathymetry Data >10/31/1998 /tiger/l/l275np/bath/l-2-75-np.335_051 >/bear/programs/edit/automerge/automerge > >Input was... >Converted to time format with year at start. > >02/14/86 BECKIE DISK$USERDISK:[CLINT.BECKIE]L275NP.335; >DRB0:[DRS.BAT]BATRED.EXE;1 >This file was hand-digetized in 2-way traveltime(secs). >It was reduced with no Matthews correction and the >velocity of sound assumed was 1500m/sec. > >02/14/86 BECKIE DISK$USERDISK:[CLINT.BECKIE]L275NP.310; >DRB0:[DRS.REFMT]REFORMAT.EXE;5 > >Input was... >Converted to time format with year at start. > >02/11/86 KAYE DUA0:[DATA.L275NP.N]L275NP.051; >DRB0:[DRS.REFMT]REFORMAT.EXE;5 > >time, lat, long, time(sec) to nearest nav fix, data values Person who carried out this activity:
    U.S. Geological Survey (USGS) , Coastal and Marine Geology (CMG)
    Attn: Carolyn H. Degnan
    Geophysicist
    USGS Pacific Coastal & Marine Science Center, 400 Natural Bridges Drive
    Santa Cruz, CA
    USA

    (831) 460-7452 (voice)
    (831) 427-4748 (FAX)
    infobank@octopus.wr.usgs.gov
    Date: 20-Jun-2012 (process 4 of 5)
    MGD77 file creation - The available data for each cruise leg are re-formatted and combined into the Marine Geophysical Data Exchange Format (MGD77) and into the internal NGDC SEIS-NAV format by USGS using several USGS developed FORTRAN programs.The FORTRAN programs sample the navigation to every integer minute of the cruise. When necessary, the latitudes and longitudes are linearly interpolated. If the time between the actual navigation fixes exceeds five minutes, no data are included in the MGD77 file.To build the MGD77 file, gravity, magnetics, and bathymetry are added to this sampled navigation. When necessary, gravity, magnetics, and bathymetry data are linearly interpolated if the time between the actual data samples does not exceed five minutes. If a time gap exceeds this, the data are not reported.The navigation data are merged with the seismic shot point data in a SEIS- NAV format file. For this file, navigation data are interpolated for each shot point. Both types of files are written to magnetic tape and sent to NGDC. Person who carried out this activity:
    U.S. Geological Survey (USGS), Coastal and Marine Geology (CMG)
    Attn: Carolyn H. Degnan
    Geophysicist
    USGS Pacific Coastal & Marine Science Center, 400 Natural Bridges Drive
    Santa Cruz, CA
    USA

    (831) 460-7452 (voice)
    (831) 427-4748 (FAX)
    infobank@octopus.wr.usgs.gov
    Date: 01-Feb-2017 (process 5 of 5)
    Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Alan O. Allwardt
    Contractor -- Information Specialist
    2885 Mission Street
    Santa Cruz, CA

    831-460-7551 (voice)
    831-427-4748 (FAX)
    aallwardt@usgs.gov
  3. What similar or related data should the user be aware of?
    Hittelman, Allen M., Groman, Robert C., Haworth, Richard T., Holcombe, Troy L., McHendrie, Graig, Smith, Stuart M., and Metzger, Dan R., 2010, The marine geophysical data exchange format - MGD77 / MGD77T: National Geophysical Data Center, National Oceanic and Atmospheric Administration, Boulder, CO.

    Online Links:

    Other_Citation_Details: 25 p.

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

  1. How well have the observations been checked?
    The validity or accuracy of bathymetry and navigation data is highly qualitative and depends on equipment and operating condition variables. Data quality is unknown, MGD77T files were formatted from InfoBank files identified as best available version.
  2. How accurate are the geographic locations?
    Unspecified
  3. How accurate are the heights or depths?
    Unspecified
  4. Where are the gaps in the data? What is missing?
    Start and end date/times of data >Navigation Data (l-2-75-np.051 [SINS]) >YYYYMMDDHHMMSST YYYYMMDDHHMMSST >197508252252000 197508301518000 >197508301606000 197508301708000 >197508301754000 197508301918000 >197508302002000 197508310031000 >197508310134000 197508310500000 >197508310546000 197508310546000 >197508310730000 197508310730000 >197508310814000 197508310918000 >197508311108000 197508311601000 >197508311720000 197508311812000 >197508311938000 197508312318000 >197509010001000 197509010001000 >197509010102000 197509010102000 >197509010301000 197509010424000 >197509010532000 197509010738000 >197509010828000 197509011028000 >197509011112000 197509011535000 >197509011618000 197509011702000 >197509011744000 197509011814000 >197509011856000 197509011918000 >197509012008000 197509012048000 >197509012130000 197509012300000 >197509020003000 197509020526000 >197509020612000 197509020632000 >197509020716000 197509020716000 >197509020808000 197509020828000 >197509020910000 197509020936000 >197509021020000 197509021631000 >197509021716000 197509021816000 >197509021900000 197509022000000 >197509022112000 197509022132000 >197509022214000 197509022214000 >197509022300000 197509022300000 >197509022342000 197509030030000 >197509030129000 197509030400000 >197509030446000 197509030502000 >197509030556000 197509030804000 >197509030852000 197509031016000 >197509031100000 197509031206000 >197509031252000 197509031500000 >197509031607000 197509031607000 >197509031700000 197509040200000 >197509040302000 197509040401000 >197509040500000 197509040531000 >197509040618000 197509040746000 >197509040832000 197509040938000 >197509041020000 197509041334000 >197509041431000 197509041500000 >197509041600000 197509041600000 >197509041702000 197509041958000 >197509042050000 197509042150000 >YYYYMMDDHHMMSST YYYYMMDDHHMMSST >Magnetics Data (l-2-75-np.220_051) >YYYYMMDDHHMMSST YYYYMMDDHHMMSST >197508252255320 197508270253040 >197508270258530 197508271629350 >197508271635350 197508280200350 >197508280234410 197508280626470 >197508280632140 197508291855480 >YYYYMMDDHHMMSST YYYYMMDDHHMMSST >Bathymetry Data (l-2-75-np.335_051) >YYYYMMDDHHMMSST YYYYMMDDHHMMSST >197509022301060 197509022301060 >197509022327360 197509022327360 >197509022353000 197509022353000 >197509030018300 197509030018300 >197509030053240 197509030053240 >197509030121480 197509030121480 >197509030152420 197509030152420 >197509030221240 197509030221240 >197509030247300 197509030247300 >197509030316180 197509030316180 >197509030344060 197509030344060 >197509030412300 197509030412300 >197509030439420 197509030439420 >197509030508420 197509030508420 >197509030541480 197509030541480 >197509030608420 197509030608420 >197509030639300 197509030639300 >197509030707000 197509030707000 >197509030738240 197509030738240 >197509030804480 197509030804480 >197509030837360 197509030837360 >197509030905480 197509030905480 >197509030934300 197509030934300 >197509031017000 197509031017000 >197509031059120 197509031059120 >197509031131300 197509031131300 >197509031203180 197509031203180 >197509031233120 197509031233120 >197509031302060 197509031302060 >197509031327540 197509031327540 >197509031405480 197509031405480 >197509031431540 197509031431540 >197509031457540 197509031457540 >197509031525480 197509031525480 >197509031555060 197509031555060 >197509031622120 197509031622120 >197509031648180 197509031648180 >197509031724060 197509031724060 >197509031750120 197509031750120 >197509031824300 197509031824300 >197509031857240 197509031857240 >197509031924240 197509031924240 >197509032018480 197509032018480 >197509032055240 197509032055240 >197509032125000 197509032125000 >197509032150360 197509032150360 >197509032221000 197509032221000 >197509032247060 197509032247060 >197509032312240 197509032312240 >197509032337420 197509032337420 >197509040002420 197509040002420 >197509040030000 197509040030000 >197509040056540 197509040056540 >197509040123540 197509040123540 >197509040149540 197509040149540 >197509040628540 197509040628540 >197509040656180 197509040656180 >197509040723060 197509040723060 >197509040751420 197509040751420 >197509040823060 197509040823060 >197509040852060 197509040852060 >197509040918300 197509040918300 >197509041000060 197509041000060 >197509041026360 197509041026360 >197509041053420 197509041053420 >197509041119120 197509041119120 >197509041211180 197509041211180 >197509041236240 197509041236240 >197509041303240 197509041303240 >197509041332480 197509041332480 >197509041400060 197509041400060 >197509041427420 197509041427420 >197509041455300 197509041455300 >197509041548540 197509041548540 >197509041625180 197509041625180 >197509041705060 197509041705060 >197509041745000 197509041745000 >197509041810000 197509041810000 >197509041837240 197509041837240 >197509041903180 197509041903180 >197509041928300 197509041928300 >197509041953360 197509041953360 >197509042020120 197509042020120 >YYYYMMDDHHMMSST YYYYMMDDHHMMSST
  5. How consistent are the relationships among the observations, including topology?
    This data set is from one field activity with unknown instrument calibrations. Processed bathymetric depths were spot checked based on latitude and longitude against the Global Multi-Resolution Topography (GMRT) grid within GeoMapApp to ensure reasonable values.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None. These data are held in the public domain.
Use_Constraints:
This information is not intended for navigational purposes. Read and fully comprehend the metadata prior to data use. Uses of these data should not violate the spatial resolution of the data. Where these data are used in combination with other data of different resolution, the resolution of the combined output will be limited by the lowest resolution of all the data. Acknowledge the U.S. Geological Survey in products derived from these data. Share data products developed using these data with the U.S. Geological Survey.This database has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use.Although this Federal Geographic Data Committee-compliant metadata file is intended to document these data in nonproprietary form, as well as in ArcInfo format, this metadata file may include some ArcInfo-specific terminology.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey
    345 Middlefield Road MS 999
    Menlo Park, CA
    USA

    (650) 329-5078 (voice)
    (650) 329-5190 (FAX)
  2. What's the catalog number I need to order this data set? Downloadable Data
  3. What legal disclaimers am I supposed to read?
    Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 01-Feb-2017
Metadata author:
Gregory K. Miller
U.S. Geological Survey
Physical Scientist
U.S. Geological Survey, 600 Fourth Street South
St. Petersburg, FL
USA

(727) 803-8747, ext. 3020 (voice)
gmiller@usgs.gov
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/pcmsc/837.faq.html>
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