Just Cerfing Vol. 7, Issue 8, August 2016 Volume 5, Issue 4, April, 2014

Previous Page Table of Contents Next Page Challenges in Building Coastal Digital Elevation Models Barry W. Eakins† and Pamela R. Grothe‡ Cooperative Institute for Research in Environmental Sciences University of Colorado Boulder, Boulder, CO 80309, U.S.A. † School of Earth and Atmospheric Sciences Georgia Institute of Technology Atlanta, GA 30332, U.S.A. ABSTRACT INTRODUCTION Digital elevation models (DEMs) support a wide variety of uses, including modeling of surface processes, habitat mapping and conservation planning, coastal change and terrain analysis, and Earth visualization and exploration. These models may, however, contain significant deviations from the surface they are intended to represent, which could reduce their usefulness. Additional complexities arise when integrating bathymetric and topographic data to create coastal DEMs. We identify common challenges in building square-cell, coastal DEMs and present some solutions. These challenges are grouped into six general categories: 1) source data, (2) data processing, (3) model development, (4) model assessment, (5) morphologic change, and (6) model uncertainty. Some DEM best practices to help improve DEM accuracy and utility include: visual inspection of source data in a geographic information system (GIS) environment; establishing common horizontal and vertical datums; using data buffers and bathymetric presurfaces; assessing DEM accuracy; accounting for morphologic change; and quantifying DEM uncertainty at the cell level. Advances in computer technology over the last few decades have made digital representations of Earth’s surface—digital elevation models (DEMs)—invaluable in many earth science applications. DEMs typically represent land elevations, but they may also include bathymetry, expanding the realm of possibilities to include modeling of ocean and coastal processes. However, unique difﬁculties may arise when integrating bathymetric and topographic data into a DEM, what we refer to as a ‘‘coastal DEM.’’ Elevation models are not a new concept. Physical models of the ground surface were being built in the sixteenth century, and by the nineteenth century, topographic maps, bathymetric charts, and cross sections became a common way of depicting elevation (Sutter, Raber, and Jenny, 2010). Miller and Laﬂamme (1958) introduced the concept of a ‘‘digital terrain model,’’ which they envisaged as a convenient, statistical representation of a continuous ground surface, and a means by which to efﬁciently obtain, via computer, numerous numerical solutions to terrain analysis problems using exact and rigorous mathematical formulations. Smith, Menard, and Sharman (1966) used this concept to develop the ﬁrst global digital model that integrated land elevations with ocean depths. This model had an average elevation every one degree of latitude, with longitudinal spacing increasing towards the poles to maintain roughly equivalent cell areas in square kilometers. Cell elevation values were derived by averaging depth/elevation measurements within the cell footprint. Public release of the U.S. Department of Defense sea-surface satellite altimetry data (Sandwell and Smith, 1997) permitted a more detailed view ADDITIONAL INDEX WORDS: DEM, bathymetry, topography, methodology, assessment, geospatial data, morphologic change, uncertainty. 18 Just Cerfing Vol. 5, Issue 4, April 2014 Continued on Next Page 19

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