Digital elevation models of Skagway and Haines, Alaska: Procedures, data sources, and quality assessment

Metadata also available as - [Parseable text] - [XML]

Frequently anticipated questions:

What does this data set describe?

Title:
Digital elevation models of Skagway and Haines, Alaska: Procedures, data sources, and quality assessment
Abstract:
In May 2014 the Geophysical Institute at the University of Alaska Fairbanks (UAF) developed integrated bathymetric‐topographic digital elevation models (DEMs) of Skagway and Haines, Alaska, for the National Tsunami Hazard Mitigation Program (NTHMP). The DEMs are designed to fit within a nested hierarchy of similar DEMs of larger spatial extent but coarser resolution. The gridded DEMs will be used to support modeling of tsunami generation, propagation, and inundation. This report describes the various source datasets, data processing tasks and techniques, the surface interpolation, and quality assessment of the seamless 8/15-arc‐second (~15 m) bathymetric-topographic DEMs. The data files are provided as ASCII raster grids with an open end-user license.
Supplemental_Information:
The DGGS metadata standard extends the FGDC standard to include elements that are required to facilitate our internal data management. These elements, referred to as "layers" group and describe files that have intrinsic logical or topological relationships and correspond to subdirectories within the data distribution package. The metadata layer provides an FGDC metadata file and may include other documentation files. Attribute information for each data layer is described in this metadata file under the "Entity_and_Attribute_Information" section. Data layer contents: 
border:    A polygon shapefile that provides a generalized outline of the geographic area described by this report.
haines-dem:    bathymetric and topographic data in ASCII raster format
skagway-dem:    bathymetric and topographic data in ASCII raster format
  1. How should this data set be cited?

    Macpherson, A.E., Nicolsky, D.J., and Suleimani, E.N., 2014, Digital elevation models of Skagway and Haines, Alaska: Procedures, data sources, and quality assessment: Miscellaneous Publication MP 155, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 15 p.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -135.540082
    East_Bounding_Coordinate: -135.283877
    North_Bounding_Coordinate: 59.495481
    South_Bounding_Coordinate: 59.188017

  3. What does it look like?

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

    Calendar_Date: 2014
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: report and 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.

    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 0.000411. Longitudes are given to the nearest 0.000411. Latitude and longitude values are specified in decimal degrees.

      The horizontal datum used is World Geodetic System of 1984.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563.

      Vertical_Coordinate_System_Definition:
      Depth_System_Definition:
      Depth_Datum_Name: Mean Higher High Water
      Depth_Resolution: 1.0
      Depth_Distance_Units: meters
      Depth_Encoding_Method: Explicit depth coordinate included with horizontal coordinates

  7. How does the data set describe geographic features?

    mp155-border
    A polygon shapefile that provides a generalized outline of the geographic area described by this report. (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))

    mp155-haines-dem
    Bathymetric and topographic data in ASCII raster format (Source: Alaska Earthquake Center, University of Alaska Fairbanks)

    mp155-skagway-dem
    Bathymetric and topographic data in ASCII raster format (Source: Alaska Earthquake Center, University of Alaska Fairbanks)

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?

    The authors thank Kelly Carignan (Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder) for sharing her time and knowledge; and George Plumley (State of Alaska, Division of Community and Regional Affairs, DCRA) for providing data used in developing the Skagway DEM. This project was supported by the National Oceanic and Atmospheric Administration under Reimbursable Services Agreement ADN 0931000 with the State of Alaska's Division of Homeland Security and Emergency Management (a division of the Department of Military and Veterans Affairs). Data acquisition for this publication is sponsored by the Cooperative Institute for Alaska Research with funds from NOAA under cooperative agreement NA08OAR4320751 with the University of Alaska Fairbanks. We thank Ken Macpherson (Alaska Earthquake Center) for his help with the RTK GPS survey in Haines and Skagway, and Nicole Kinsman (Alaska Division of Geological & Geophysical Surveys) for her valuable comments and suggestions to improve the manuscript.

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

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

    (907)451-5020 (voice)
    dggsgis@alaska.gov

    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays

Why was the data set created?

In May 2014 the Geophysical Institute at the University of Alaska Fairbanks (UAF) developed integrated bathymetric‐topographic digital elevation models (DEMs) of Skagway and Haines, Alaska, for the National Tsunami Hazard Mitigation Program (NTHMP). The DEMs are designed to fit within a nested hierarchy of similar DEMs of larger spatial extent but coarser resolution. The gridded DEMs will be used to support modeling of tsunami generation, propagation, and inundation.

How was the data set created?

  1. From what previous works were the data drawn?

    Caldwell, R.J. and others, 2011 (source 1 of 1)
    Caldwell, R.J., Eakins, B.W., and Lim, E., 2011, Digital elevation models of Prince William Sound, Alaska-Procedures, data sources and analysis: NOAA Technical Memorandum NESDIS NGDC-40, National Geophysical Data Center, Marine Geology and Geophysics Division, United States.

    Type_of_Source_Media: paper
    Source_Contribution: DEM Development

  2. How were the data generated, processed, and modified?

    Date: 2014 (process 1 of 6)
    Coastline - Digital MHW coastline positions were extracted from National Oceanic and Atmospheric Administration's (NOAA's) Office of Coast Survey (OCS) ENC (Electronic Navigational Chart) Direct-to-GIS online extraction service1. A cartographic coastline dataset created by the Alaska Department of Natural Resources, Information Resource Management Section, at a scale of 1:63,3602, was downloaded from the Alaska State Geo‐Spatial Data Clearinghouse (ASGDC). The coastlines were compared and edited to match high-resolution imagery and topographic data provided by the Alaska Mapped3 program and the Geographic Information Network of Alaska's (UAF-GINA's) Best Data Layer Web Mapping Service to create a final coastline product. The ENC coastline conformed most closely to the imagery but did contain some gaps that required manual, heads‐up digitizing from the imagery at a scale of roughly 1:3,000. A complete list of references can be found in the accompanying report.

    Date: 2014 (process 2 of 6)
    Bathymetry - We assembled various bathymetric data. Bathymetric data were transformed to WGS84 and MHHW datums as needed. Where recent, higher-resolution data exist, older data were ignored. Vertical datum transformations were conducted with a sole-station offset based on the NOAA tide station (tidal station # 9452400) in Skagway. Because Haines is in close proximity to Skagway, connected by deep water, and has no independent tide station, we infer the local MHHW datum for Skagway as a best-available approximation for the local MHHW datum in Haines. A complete list of references can be found in the accompanying report.

    Date: 2014 (process 3 of 6)
    Topography - We evaluated several sources of topographic data for use in this project. Alaska's Division of Community and Regional Affairs (DCRA) provided topographic data for Skagway. No comparable DCRA dataset exists for Haines and further research did not reveal any other suitable topographic data. ArcGIS was used to transform the CAD files (DCRA dataset) to shapefiles. The National Elevation Dataset (NED) DEM provided full topographic coverage at 1/3-arc second. Vertical datum transformations were based on the NOAA tide station in Skagway. Topographic data used in developing the Skagway and Haines DEMs is listed in table 4 of the accompanying report.

    Date: 2014 (process 4 of 6)
    RTK GPS Data Collection - The available topographic datasets are augmented with a real-time kinematic (RTK) GPS survey in the harbor areas and along nearshore areas in Skagway and Haines. The survey in Skagway was conducted October 18-20, 2013, and the survey in Haines October 22-24, 2013. The collected GPS measurements had 0.03-0.05 m (1.2-2 in) horizontal and vertical accuracy with respect to the base station (Leica Geosystems AG, 2002). To achieve sub-meter accuracy for all GPS measurements relative to the MHHW datum, the base station must be linked to the MHHW datum with sub-meter accuracy. This level of accuracy can be achieved if the base station is set up at an established tidal benchmark with a known geodetic elevation. No conveniently located tidal benchmark was available in Skagway for this survey, and there are no listed tidal benchmarks in Haines8. Therefore, we converted the collected GPS measurements to the MHHW datum using a technique described in the the accompanying report.

    Date: 2014 (process 5 of 6)
    DEM Development - After horizontal and vertical transformations were applied in ArcGIS, the resulting ESRI shapefiles were reviewed in ArcMap and QT Modeler for consistency among datasets. Problems and errors were identified and resolved before proceeding with subsequent gridding steps. Some fixes and preliminary steps included: Where there were inconsistent, overlapping bathymetry and topography datasets, older data were clipped to newer data and only used in those areas where gaps in newer data coverage existed. The NED topographic data were clipped to the adjusted ENC coastline. A careful visual inspection of the bathymetric/topographic interface was conducted to ensure there were no artificial cliffs in the DEM. This area displays a rugged coastline with some steep cliffs along the shore and the DEM was inspected to confirm these also appeared correctly in the final dataset. Bathymetric data were lacking in the delta region of McClellan mudflats, so MHW elevations were pulled from existing NOAA DEM at 8/3-arc‐second resolution, transformed, and edited to more smoothly transition to the boundary with NOS survey data and topographic data. The central flat area was adjusted to zero elevation and then interpolated toward the coast and deeper waters where survey data existed. Elevations at Haines Airport runway were adjusted minimally (less than 1 m) to match documented survey elevations. We used the shapefiles discussed in the preceding sections of this report as input into the Tensioned Spline function of ArcGIS' Spatial Analyst extension to construct the seamless bathymetric-topographic DEM. The Tensioned Spline tool performs a spline interpolation of input data‐point values to create a raster dataset in which the surface passes exactly through the input x-y-z data and interpolates values for cells with no data. A weight parameter of 1 was used in order to create a surface that closely fits the input control points. The use of this interpolation method conforms to techniques used for the creation of other NGDC DEM products.

    Data sources used in this process:

    • Caldwell, R.J. and others, 2011

    Date: 2014 (process 6 of 6)
    DEM Analysis - The completed Skagway and Haines DEMs were visually compared to nautical charts, topographic maps, and high-resolution imagery. A color classification was applied to the seamless DEM to separate positive and negative values. The coastline was meticulously scrutinized with respect to both the final coastline vector data and high-resolution imagery in GINA's Best Data Layer Web Mapping Service. Final DEMs were reviewed in three-dimensional (3-D) space using Quick Terrain Modeler software and ESRI ArcScene. The DEMs were also compared closely to the UAF GPS collection using a custom MatLab program to check for inconsistencies, to adjust contouring along the shore, and to improve the depiction of breakwaters and jetties where there were sparse source data points.

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

    Hickman, P.J., Suleimani, E.N., and Nicolsky, D.J., 2012, Digital elevation model of Sitka Harbor and the city of Sitka, Alaska: Procedures, data sources, and quality assessment: Miscellaneous Publication MP 144, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 38 p

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

  1. How well have the observations been checked?

    The accuracy of this elevation grid is dependent on the accuracy of its source data. The primary limiting factors include the scale, age, and resolution of the surveys. A significant amount of quality control was performed on the grid, using initial data points and other sources for comparison.

  2. How accurate are the geographic locations?

    A comparison of the UAF-surveyed GPS points to the existing NGDC 8/3-Arc Second DEM for Southeast Alaska versus the UAF GPS points as compared to the new Skagway and Haines DEMs shows a marked improvement for elevations at these surveyed areas. Histograms and specific summary statistics of these results are provided in figures 12-18 of the accompanying report.

  3. How accurate are the heights or depths?

    A comparison of the UAF-surveyed GPS points to the existing NGDC 8/3-Arc Second DEM for Southeast Alaska versus the UAF GPS points as compared to the new Skagway and Haines DEMs shows a marked improvement for elevations at these surveyed areas. Histograms and specific summary statistics of these results are provided in figures 12–18 of the accompanying report.

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

    The completed Skagway and Haines DEMs were visually compared to nautical charts, topographic maps, and high-resolution imagery. A color classification was applied to the seamless DEM to separate positive and negative values. The coastline was meticulously scrutinized with respect to both the final coastline vector data and high-resolution imagery in GINA's Best Data Layer Web Mapping Service. Final DEMs were reviewed in three-dimensional (3-D) space using Quick Terrain Modeler software and ESRI ArcScene. The DEMs were also compared closely to the UAF GPS collection using a custom MatLab program to check for inconsistencies, to adjust contouring along the shore, and to improve the depiction of breakwaters and jetties where there were sparse source data points.

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

    We constructed two new 8/15-arc second bathymetric-topographic DEMs to support numerical tsunami wave inundation modeling and mapping in the communities of Skagway and Haines, Alaska. The spatial resolution of these grid cells satisfies NOAA minimum recommended requirements for computation of tsunami inundation. Additional requirements are detailed by the NTHMP Mapping & Modeling Subcommittee. The new DEMs were also produced in accordance with NGDC best practices, using the highest-resolution and most current hydrographic surveys, and the best topographic datasets available to us at this time. We ensured that the horizontal geographic coordinates for all data points incorporated during the construction of this DEM are correctly referenced to the WGS84 horizontal datum and that all of the depth values are referenced to the MHHW vertical datum. A detailed discussion of the methods and sources used to generate these files can be found in the accompanying report.

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 & 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?

    MP 155

  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?

Who wrote the metadata?

Dates:
Last modified: 15-Dec-2014
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 Mon Dec 15 17:24:47 2014