High-resolution lidar data for infrastructure corridors, Anchorage Quadrangle, Alaska

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Frequently anticipated questions:

What does this data set describe?

Title:
High-resolution lidar data for infrastructure corridors, Anchorage Quadrangle, Alaska
Abstract:
In advance of design, permitting, and construction of a pipeline to deliver North Slope natural gas to out-of-state customers and Alaska communities, the Division of Geological & Geophysical Surveys (DGGS) has acquired lidar (Light Detection and Ranging) data along proposed pipeline routes, nearby areas of infrastructure, and regions where significant geologic hazards have been identified. Lidar data will serve multiple purposes, but have primarily been collected to (1) evaluate active faulting, slope instability, thaw settlement, erosion, and other engineering constraints along proposed pipeline routes, and (2) provide a base layer for the state-federal GIS database that will be used to evaluate permit applications and construction plans. Bare-earth digital elevation models (DEM) represent the earth's surface with all vegetation and human-made structures removed.
Supplemental_Information:
This metadata file was written to document and describe, as a whole, all the bare-earth digital elevation model files generated for this project. The original metadata files provided by Watershed Sciences, Inc are also included in the download package and may provide additional useful information that is specific to each file. The metadata files provided by Watershed Sciences, Inc. have not been reviewed for accuracy or compliance with FGDC standards. For each data delivery area, reports documenting data collection methodology, accuracy, and quality control were provided by Watershed Sciences and the Oregon Department of Geology and Mineral Industries (DOGAMI). These reports have been combined into single comprehensive reports organized by delivery region. The lidar QC report (the comprehensive report from DOGAMI) and the lidar delivery report (the comprehensive report from Watershed Sciences) can be found at <http://dx.doi.org/10.14509/22722>. Information about the quadrangles included in individual delivery regions can be found in the lidar delivery index report included with the data download. The DGGS metadata standard extends the FGDC standard to include several elements that are required to facilitate internal data management. These elements are refered to as layers. This dataset is described as a single layer titled: 
bare_earth_dem	bare-earth digital elevation model (DEM)
  1. How should this data set be cited?

    Hubbard, T.D., Braun, M.L., Westbrook, R.E., and Gallagher, P.E., 2011, High-resolution lidar data for infrastructure corridors, Anchorage Quadrangle, Alaska: Raw Data File RDF 2011-3L, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys, Fairbanks, Alaska USA.

    Online Links:

    This is part of the following larger work.

    Hubbard, T.D., Koehler, R.D., and Combellick, R.A., 2011, High-resolution lidar data for Alaska infrastructure corridors: Raw Data File RDF 2011-3, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys, Fairbanks, AK USA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -150
    East_Bounding_Coordinate: -147
    North_Bounding_Coordinate: 62
    South_Bounding_Coordinate: 61

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 2010
    Ending_Date: 2011
    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, 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: 6
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -147
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 0.000000

      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 1.000000
      Ordinates (y-coordinates) are specified to the nearest 1.000000
      Planar coordinates are specified in meters

      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 1/298.257222.

      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: North American Vertical Datum of 1988
      Altitude_Resolution: 0.0000001
      Altitude_Distance_Units: feet
      Altitude_Encoding_Method: Attribute values

  7. How does the data set describe geographic features?

    be
    Bare earth digital elevation model (DEM) (Source: this report)

    Entity_and_Attribute_Overview:
    There are no attributes other than the encoded values for easting and northing coordinates.
    Entity_and_Attribute_Detail_Citation: this report
    Overview_Description_Layer_Name: bare_earth_dem

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

    Data collection was supported by funding from the Department of Natural Resources (DNR), Division of Geological & Geophysical Surveys (DGGS), the Alaska Gas Pipeline Project Office, the Office of the Federal Coordinator, and the Alaska Gasline Development Corporation (AGDC). Lidar data were collected and processed by Watershed Sciences of Corvallis, Oregon. Survey data were collected by McClintock Land Associates of Eagle River, AK. Lidar data and derivative products were checked for quality, completeness, and accuracy by State of Oregon Department of Geology & Mineral Industries based in Portland, OR.

  3. To whom should users address questions about the data?

    Alaska Division of Geological &amp; Geophysical Surveys
    Attn: James Weakland
    GIS Analyst
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907)451-5029 (voice)

Why was the data set created?

Provide high-resolution terrain elevation data.

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: 2010 (process 1 of 6)
    Acquisition: The lidar data were collected between September and October 2010 and between May and July 2011. The survey used the Leica ALS60 system. Near-nadir scan angles were used to increase penetration of vegetation to ground surfaces. Ground-level GPS and aircraft IMU were collected during the flight.

    Date: 2010 (process 2 of 6)
    Processing lidar data: (1) Flight lines and data were reviewed to ensure complete coverage of the study area and positional accuracy of the laser points. (2) Laser point-return coordinates were computed using ALS Post Processor software, IPAS Pro GPS/INS software, and Waypoint GPS, based on independent data from the lidar system, IMU, and aircraft. (3) The raw lidar file was assembled into flight lines per return with each point having an associated x, y, and z coordinate. (4) Visual inspection of swath-to-swath laser point consistencies in the study area were used to perform manual refinements of system alignment. (5) Custom algorithms were designed to evaluate points between adjacent flight lines. Automated system alignment was computed based on randomly selected swath-to-swath accuracy measurements that consider elevation, slope, and intensities. Specifically, refinement in the combination of system pitch, roll, and yaw-offset parameters optimize internal consistency. (6) Noise (e.g., pits and birds) was filtered using ALS post processing software, based on known elevation ranges, and included the removal of any cycle slips.

    Date: 2010 (process 3 of 6)
    Hydro-flattening: A combination of automated and manual detection and adjustment techniques was used to identify lake boundaries and water levels for closed water bodies with a surface area > 150 square meters. Boundary polygons were developed using an algorithm that weights lidar - derived slopes, intensities, and return densities to detect the lake edge. Once detected, lake edges were manually reviewed and edited in a 3-D environment, and polygons were created with elevations computed from the filtered lidar returns. During the initial ground-modeling process returns from the water surface within each polygon were filtered and inspected for false low points. The elevation of each lake was computed as 5 cm above the minimum elevation of filtered-water surface cells within the lake polygon. Lake-boundary polygons were then incorporated into the final terrain model and enforced as hard breaklines. The initial ground classified-points falling within lake polygons were reclassified as water points and omitted from the final bare-earth DEM.

    Date: 2011 (process 4 of 6)
    Creation of bare-earth DEMs: (1) The TerraScan software suite was used to classify near-ground points. Geometric constraints were used to remove all points not near the earth. The resulting bare-earth ground model was then visually inspected and additional ground modeling was performed in site-specific areas to improve ground detail. (2) The corrected and filtered return points were compared to the real-time kinematic (RTK) ground survey points collected to verify the vertical and horizontal accuracies. (3) Points were output as laser points and, TINed, and GRIDed surfaces to create the bare-earth DEM.

    Date: 2011 (process 5 of 6)
    A metadata file was created to generally describe data acquisition of lidar and creation of bare-earth DEM's for the entire project.

    Date: 2011 (process 6 of 6)
    The bare earth digital elevation models (DEM) represent the earth's surface with all vegetation and human-made structures removed. The bare earth DEMs were derived from LiDAR data using TIN processing of the ground point returns. The DEM grid cell size is 1 meter. The elevation units are in meters. Some elevation values have been interpolated across areas in the ground model where there is no elevation data (e.g. over dense vegetation, water).

  3. What similar or related data should the user be aware of?

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

  1. How well have the observations been checked?

    Absolute accuracy refers to the mean vertical offset of lidar data relative to measured ground-control points (GCP) obtained throughout the lidar sampling area. Ground control points were collected by McClintock Land Associates, a licensed surveying company, to be used as control comparison with lidar elevations. Refer to the lidar delivery report and lidar QC report for more details on the accuracy of the lidar data for each delivery area, including a comparison of GCP elevations with bare-earth digital elevation model elevations.

  2. How accurate are the geographic locations?

    True horizontal accuracy is regarded as a product of the lidar ground footprint. Lidar is referenced to co-acquired GPS base station data that have accuracies far greater than the value of the lidar footprint. The ground footprint is equal to 1/3333rd of the above - ground flying height. The ground footprint for data collected for this project exceeds typical accuracy of ground control used to reference the lidar data (less than 0.01 meters). Project specifications require the lidar footprint to be between 0.15 and 0.40 meters. Refer to the lidar QC report and lidar delivery report for additional information on horizontal accuracy for individual delivery areas.

  3. How accurate are the heights or depths?

    Vertical accuracy was assessed by comparing GPS survey collected by McClintock Land Associates with lidar digital elevation models to expose offsets. Project specifications list the maximum root mean square vertical offset to be 0.20 meters. Please see the lidar QC report and lidar delivery report for statistics from vertical accuracy analysis for individual delivery areas.

  4. Where are the gaps in the data? What is missing?

    Lidar data have been checked for accuracy and completeness. Please refer to the lidar delivery report and lidar QC report for details about data accuracy completeness for individual delivery sets.

  5. How consistent are the relationships among the observations, including topology?

    Lidar data have been examined to ensure that overlapping flight lines have consistent elevation values. Project specifications require that lidar consistency, measured as vertical offsets between adjacent flight lines, must average less than 0.15 meters. Refer to the lidar QC report and the lidar delivery report for statistics from consistency analyses for individual delivery sets. Flight lines have been examined to ensure that there was at least 60% sidelap and that there are no data gaps. Shaded relief, lidar slope, and bare-earth digital elevation model (DEM) images have been visually inspected for data errors such as pits, border artifacts, gaps, and shifting. Additionally, all file naming conventions and formats have been checked for consistency.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints:
This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological &amp; Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.

  1. Who distributes the data set? (Distributor 1 of 1)

    Alaska Division of Geological & Geophysical Surveys
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov

    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (<http://www.dggs.alaska.gov>) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
  2. What's the catalog number I need to order this data set?

    RDF 2011-3L

  3. What legal disclaimers am I supposed to read?

    The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.

  4. How can I download or order the data?

  5. Is there some other way to get the data?

    DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media over the counter, by mail, phone, fax, or email from the DGGS Fairbanks office. Turnaround time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for exact shipping amount.

Who wrote the metadata?

Dates:
Last modified: 20-Aug-2013
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Metadata Manager
3354 College Road
Fairbanks, AK 99709-3707
USA

(907)451-5020 (voice)

Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.9.21 on Tue Aug 20 16:07:59 2013