Tutuila Coastal Terrain Model (CTM), 5-m grid "tutctm022108"

Frequently-anticipated questions:

What does this data set describe?

Title: tutctm022108
This dataset is a compilation of a USGS 1:24000 DEM, multibeam sonar bathymetry and bathymetry derived from Ikonos satellite imagery to provide for terrestrial data, depths from 15 m to 250 m and depths from 0 m to 15 m, respectively. The resulting compilation is a coastal terrain model (CTM) of the island of Tutuila, American Samoa. The image processing required to derive bathymetry from spectral data were performed using the software package ENVI 4.3. The DEM, multibeam bathymetry and derived bathymetry datasets were compiled and regridded using the ArcGIS 9.2 software package. Cell resolution is 5 m. The CTM was created to support terrain analyses that cross the land-sea interface to study the impact of human settlement density to the health of coral reefs. This dataset was created by Kyle Hogrefe as part of his M.S. thesis entitled Derivation of Near-shore Bathymetry from Multispectral Satellite Imagery Used in a Coastal Terrain Model for the Topographic Analysis of Human Influence on Coral Reefs available from Oregon State University. Additionally a peer-reviewed journal article, Derivation and Integration of Shallow-water Bathymetry: Implications for Coastal Terrain Modeling and Subsequent Analyses, will appear in the journal Marine Geodesy in a December 2008 special issue.
  1. How should this data set be cited?

    Hogrefe, K.R., Wright, D.J., and Hochberg, E.J., Derivation and integration of shallow-water bathymetry: Implications for coastal terrain modeling and subsequent analyses, Marine Geodesy, 31(4): 299-317, 2008.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -170.928197
    East_Bounding_Coordinate: -170.484814
    North_Bounding_Coordinate: -14.195329
    South_Bounding_Coordinate: -14.384031

  3. What does it look like? See dusk.geo.orst.edu/djl/samoa/CTM_thumb.jpg

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

    Calendar_Date: Ikonos Imagery: 11/07/2001 - 2/03/2002
    Currentness_Reference: Data source aquisition/creation dates

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

    Geospatial_Data_Presentation_Form: Fgdb 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 4162 x 9559 x 1, type Pixel

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      UTM_Zone_Number: -2
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -171.000000
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 10000000.000000

      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 5.000000
      Ordinates (y-coordinates) are specified to the nearest 5.000000
      Planar coordinates are specified in meters

      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 1/298.257224.

  7. How does the data set describe geographic features?

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?

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

    Kyle Hogrefe
    Oregon State Universtiy


Why was the data set created?

This is a compilation of terrestrial and bathymetric datasets, a USGS DEM, nearshore bathymetry derived from Ikonos sattelite imagery and gridded multibeam sonar data, into a coastal terrain model (CTM). The CTM was created to support terrain analyses that cross the land-sea interface to study the impact of human settlement density to the health of coral reefs.

Abstract of the thesis for which this dataset was created: The analysis of material and energy exchange between the marine and terrestrial components of island ecosystems enables research into the impact of human population and land use on the health of coral reef habitat. Satellite and acoustic remote sensing technologies enable the collection of data to produce high resolution bathymetry for integration with terrestrial digital elevation models (DEMs) into coastal terrain models. An integrated terrain surface that incorporates the land-sea interface, grounded by a geographic information system, is a powerful analytical tool for geomorphic studies of watersheds and coastal processes. The island of Tutuila, American Samoa is an ideal case study due to its high relief terrain, data availability and local interest in impacts to coral reef resources. The Tutuila model integrates a USGS DEM, multibeam bathymetry from 15 to 500 m and near shore bathymetric data from 0 to 15 m derived from IKONOS satellite imagery. The high spatial resolution of IKONOS imagery is suitable for detection of features with subtle relief and intricate structure. Shallow water bathymetry is derived by quantifying the relative attenuation of blue and green spectral band radiance as a function of depth. The procedure used to derive bathymetry, Lyzenga (1985), is identified as the most effective of several proposed in the recent literature. The product is error-checked using control points extracted from multibeam sonar data and collected during recent field surveys, as well as terrain profiles. The coastal terrain model provides morphological detail of fine resolution and high accuracy for terrain and land use analysis to enhance the study of ecosystem interconnectivity and the effects of anthropogenic inputs to coral reef habitats. Subsequent topographic analyses of the Tutuila model use drainage patterns to identify contiguous marine/terrestrial basins within which the marine environment is most directly impacted by land use through freshwater inputs from affiliated catchments. Human population density serves as an indicator of intensified land use and urbanization, which has been shown to increase pathogen and sediment loads in runoff, while percent coral cover, coral colony density and coral genera diversity are used as indicators of reef health. Spatiotemporal correlation analyses of population density against the three reef health indices within each of the marine/terrestrial basins reveal a decline in reef health associated with increased population density. This paper integrates and builds upon established methods of satellite imagery analysis and terrain modeling to create the Tutuila coastal terrain model and uses it to refine the scale of other studies linking human terrestrial activities to the physical condition of coral reefs.

How was the data set created?

  1. From what previous works were the data drawn?

    Many thanks to NOAA’s Pacific Island Fisheries Science Center, Coral Reef Ecosystem Division and the Pacific Islands Benthic Habitat Mapping Center for collecting field control points and for providing the multi-beam sonar data.

    Thanks also to NOAA’s Center for Coastal Monitoring and Assessment, Biogeography Team for providing at-sensor Ikonos satellite data.

    DEM (source 1 of 3)
    Type_of_Source_Media: data server download
    Source_Contribution: Terrestrial Topography

    IKONOS Imagery (source 2 of 3)
    Type_of_Source_Media: data server download
    Source_Contribution: Source of spectral data used to derive bathymetry.

    Multibeam Sonar (source 3 of 3)
    Type_of_Source_Media: data server download
    Source_Contribution: Bathymetry data from ~10 meters to 250 meters.

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

    Date: 2007-'08 (process 1 of 3)
    The DEM was reprojected from NAD83_GRS80 to WGS84_UTMz2s, regridded from a 10 meter to a 5 meter resolution and integrated with the other datasets.

    For a detailed description of processing: <Cookbook_042108.pdf>

    Person who carried out this activity:

    Kyle Hogrefe


    Data sources used in this process:
    • DEM

    Date: 2007-'08 (process 2 of 3)
    The IKONOS imagery went through multiple processing steps to derive bathymetry as follows (in summary):

    File conversion Data conversion from digital number to radiance values Corrected for atmosphere and water surface reflection (deglinting) Linearization of spectral decay as a function of depth Georectification of spectral data with multibeam sonar data Derivation of bathymetry data from linearized spectral values Integration with other datasets

    For a detailed description of processing: <Cookbook_042108.pdf>

    Person who carried out this activity:

    Kyle Hogrefe


    Data sources used in this process:
    • IKONOS Imagery

    Date: 2007-'08 (process 3 of 3)
    The data were recieved as an ASCII file and needed to be converted to a GRD file and have its geographical references defined. Gaps in the raster data were filled using a moving window algorithm in ArcGrid command line before being integrated with other datasets.

    For a detailed description of processing: <Cookbook_042108.pdf>

    Person who carried out this activity:

    Kyle Hogrefe


    Data sources used in this process:
    • Multibeam Sonar

  3. What similar or related data should the user be aware of? See other coastal terrain models created by Kyle Hogrefe at dusk.geo.orst.edu/djl/samoa

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

  1. How well have the observations been checked?

    The elevation data are accurate to within the 10 meter contour interval of the original USGS 1:24000 topographic map. The gridded multibeam bathymetry is corrected for platform and tidal parameters and are presumed to be accurate to within a few meters. The derived bathymetry shows a consistant 5 m or greater overestimation of depth in the shallow range (< 5 m) and underestimation of depth the deep range (> 15 m).

  2. How accurate are the geographic locations?

    There is a potential offset of 10-15 meters in the derived bathymetry due to the same offset in original IKONOS imagery.

  3. How accurate are the heights or depths?

    Potential offset between DEM and multibeam sonar bathymetry of < .3 meters due to a vertical datum conflict.

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

    There were gaps in the original multibeam data where sonar swaths did not overlap. There were gaps in the derived bathymetry data as a result of cloud cover, surf zones and emergent reefs. For the purpose of creating a constant surface for the CTM, these data gaps where filled using a moving window algorithm through the ArcGrid command line window that assigned values to NoData cells based on the values of a defined range of nearby cells.

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

    All internally, logically consistent. Arc-node topology not applicable for this raster grid.

How can someone get a copy of the data set?

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

Access_Constraints: None
Not for navigational purposes. Please cite authors when using the data for your own work in print or on the web.

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

    Davey Jones' Locker GIS Lab, Oregon State University


  2. What's the catalog number I need to order this data set?

    Downloadable Data

  3. What legal disclaimers am I supposed to read?


  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 08-Oct-2008
Metadata author:
Davey Jones Locker GIS Lab, Oregon State University
c/o Kyle Hogrefe, Dawn Wright
104 Wilkinson Hall, Oregon State University
Corvallis, OR 97331-5506

541-737-8818 (voice)

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

Generated by mp version 2.8.6 on Wed Oct 08 11:15:18 2008