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Semi-automated Methods to Create a Hydro-flattened DEM using Single Photon and Linear Mode LiDAR Points

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2017, Doctor of Philosophy, Ohio State University, Geodetic Science.
LiDAR pulses are mostly absorbed by water bodies, thereby creating voids. The LiDAR points available over water surfaces are not reliable due to near water surface features such as: ripple, waves, or near surface ground objects. A bare ground DEM surface, created using such points, result in an uneven water surface which appears unnatural and cartographically unpleasing. Contours, created using such surface, are not consistent with the USGS contours, which are produced using traditional methods. Hence, the LiDAR point cloud needs to be hydro-flattened to produce a bare ground surface, consistent with the traditionally produced DEMs. Hydro-flattening is the process of creating a LiDAR-derived DEM where the water surfaces appear and behave as they would in a traditional topographic DEM generated from photogrammetric digital terrain models (DTMs). Hydro-flattened DEMs, created using LiDAR data, exclude LiDAR points over water bodies and include three-dimensional (3D) bank shorelines. In this dissertation, a methodology for creating hydro-flattened bare ground surfaces using linear mode (LM) or Single Photon (SP) LiDAR point clouds is presented. First the properties of both the sensors are compared and the need of hydro-flattening is discussed. Then, the method is described in detail for both the sensors. LiDAR point cloud and an approximate stream centerline are the primary data for this process. In the first step, a continuous bare ground surface (CBGS) is created by eliminating non-ground LiDAR points and adding artificial underwater points. In the second step, the lowest elevation from the LiDAR point cloud, within a radius distance from the river centerline is used to create a virtual water surface (VWS). This VWS is revised to consider water surface undulations such as ripples or waves, protruding underwater objects, etc. The revised VWS is then intersected with the CBGS to locate the two-dimensional (2D) bank shorelines. The 2D shorelines are assigned the elevations of the VWS and are used to produce a hydro-flattened DEM. This methodology is developed for either classified or unclassified LiDAR point clouds. The method proposed is adapted for both LM and SP LiDAR point clouds. Data at three sites are tested to check the consistency of the proposed methodology. Only a LM LiDAR point cloud is available at the Michigan site. The results from this site show that the horizontal accuracies observed between the bank shoreline, extracted using raw LiDAR points, and the GPS survey of the 2D shoreline are 0.94 m, 0.69 m, and 0.63 m for the three water surfaces, respectively. The accuracies attained using vendor classified LiDAR points are 0.74 m, 0.67 m, and 0.64 m which are very similar to those using raw LiDAR points. Both SP and LM LiDAR are processed at the second site, located in North Carolina. The results at this site are compared to orthoimages. The results show that the 2D bank shoreline appears very close to the orthoimages compared to the 2D shoreline obtained using the LM LiDAR point cloud. This is due to the high resolution of the SP LiDAR points. Only SP LiDAR is analyzed at the third site, located in Connecticut. The results at this site confirm that the SP LiDAR point cloud produces higher quality 2D bank shoreline and thus produces a better hydro-flattened surface.
Alper Yilmaz, PhD (Advisor)
Alan Saalfeld, PhD (Committee Member)
Charles Toth, PhD (Committee Member)
145 p.

Recommended Citations

Citations

  • Deshpande, S. S. (2017). Semi-automated Methods to Create a Hydro-flattened DEM using Single Photon and Linear Mode LiDAR Points [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1491300120665946

    APA Style (7th edition)

  • Deshpande, Sagar. Semi-automated Methods to Create a Hydro-flattened DEM using Single Photon and Linear Mode LiDAR Points. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1491300120665946.

    MLA Style (8th edition)

  • Deshpande, Sagar. "Semi-automated Methods to Create a Hydro-flattened DEM using Single Photon and Linear Mode LiDAR Points." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1491300120665946

    Chicago Manual of Style (17th edition)