Online Merging and Gridding of Topographic and Bathymetric Data Sources

Digital Elevation Models (DEM) provide details of the earth’s surface and are used for visualization, physical modeling, and elevation change analysis. Creating DEMs in coastal environments is complicated by the highly ephemeral nature of the coast and the need to span the land-water interface.  This requires merging multiple bathymetric and topographic datasets that have been collected at different times, using different instrument platforms with varying levels of accuracy, and with variable spatial resolution and coverage.  Because coastal change can occur over relatively short time scales (days to weeks in the case of storms), rapid updates to coastal DEMs are also needed. These challenges and the lack of available tools to create coastal DEMs, lead scientists to sacrifice accuracy by  1) relying on previously merged, outdated, or over-smoothed DEMs; 2) discarding more recent data that covers only a portion of the DEM; and 3) using inconsistent methodologies to generate DEMs.  While there are existing projects using sophisticated GIS tools to create DEMs in some specific coastal regions, the process is time-consuming and may not meet the needs of individual scientists and resource 

managers.



Principal Investigator : Joseph W Long, Sky Bristol



The objective of this work was to develop an online, on-demand tool to integrate land and water-based elevation data sources and create DEMs driven by user specifications.  To achieve this, we developed an ArcGIS web processing service to format and initialize Python-based geoprocessing tasks (e.g. Plant et al 2002) designed to create on-demand coastal DEMs.  The web processing service is maintained within the USGS ScienceBase data management system and has an associated user interface.  



Through the map-based interface, users define a geographic region that identifies the bounds of the desired DEM and a time period of interest. In addition to any user-supplied elevation data, this initiates a query for elevation datasets available within federal science agency data repositories.  The geoprocessing service is then triggered to interpolate, merge, and smooth the data sources utilizing the user-defined configuration parameters (resolution, smoothing scales, error thresholds, etc).  Uncertainty and error estimates for the DEM are also returned by the geoprocessing service.  Upon completion, the information management platform provides access to the final gridded data derivative and saves the configuration parameters for future 

reference by all users.



The benefits of this online tool include increased access and utilization of USGS elevation products through easily generated coastal DEMs and reduced overhead costs for coastal researchers and managers who rely on these elevation products.  By providing this service we anticipate an increased consistency among coastal elevation models and by making the geoprocessing codes open source, they can continue to be enhanced by the research 

community.  Also, as a result of this project, the ScienceBase data management system has been improved and is now capable of housing web processing items and ingesting and storing new filetypes. 



Deliverables: 

• The framework was presented at the Federation for Earth Science Information Partners 2014 summer meeting (Frisco, CO)
• The project PI was invited to present the project status at the American Geophysical Union 2014 Fall meeting (San Francisco, CA).
• Web processing service publicly available on ScienceBase; upload and process input data; store and share processed DEMs (anticipated by:  August 31, 2015)
• Geoprocessing code dissemination on https://github.com  (anticipated date: May 31, 2015)

References List: 

Plant, Nathaniel G., K. Todd Holland, and Jack A. Puleo. "Analysis of the scale of errors in nearshore bathymetric data." Marine Geology 191.1 (2002): 71-86.



Caption for visual representation:



Framework for online, on-demand tool to create coastal digital elevation models (DEM).  Users define an area of interest using the example web interface (top panel).  Based on a query of elevation resources, relevant datasets in the selected region is identified (middle panel) where, in this example, bathymetric data is shown in red and locations of topographic data in black.  Finally, the geoprocessing service merges, interpolates, and smooths the data into a DEM utilizing the user-defined requirements (bottom panel).



Note:  this description is from the FY14 CDI Annual Report