2023 A2HRT RCN - Topographic differencing

2023 A2HRT RCN: Vertical Topographic Differencing, Error Budgets, Vertical Datums

Instructors:

Chelsea Scott and Craig Glennie

Description:

This 2.5 hour training, created for the 2023 EarthCube Advancing the Analysis of HRT (A2HRT) Workshop, will begin with lectures on vertical differencing, reference frames, and datums. In the following hands-on session, participants will learn how to conduct vertical differencing of high resolution topography in QGIS. We will explore cases where topographic data are ready for differencing and cases that require a projection of the vertical coordinate reference system prior to differencing.

Recommended Reading:

Measuring change at Earth’s surface: On-demand vertical and three-dimensional topographic differencing implemented in OpenTopography .

Outline:

  • 1 hr, Lecture and discussion on vertical differencing, reference frames & datums
  • 1 hr, 30 mins, Activity on vertical differencing & datums

    • Required software

    QGIS

    Activity 1: Vertical differencing

    Vertical differencing of datasets already in the same coordinate reference system. Display the differencing results using this red-white-blue QGIS style-file. .

    Difference = Reference (later dataset) - compare (earlier dataset)

    Susquehanna Critical Zone Observatory, PA

    Data for differencing
    Compare dataset: July 2010 from the Susquehanna Shale Hills Critical Zone Observatory: Leaf On Survey
    Reference dataset: December 2010 from the Susquehanna Shale Hills Critical Zone Observatory: Leaf Off Survey

    Salt Lake City, UT

    Data for differencing
    Compare dataset: Utah 2011 from the Utah Geological Survey Lidar
    Reference dataset: Utah 2014 from the 2015-2017 State of Utah Lidar Acquisition

    Activity 2: Vertical differencing, correcting vertical datums

    Vertical differencing of datasets with different vertical datums

    gdalwarp to remove geoid-> -s_srs "+proj=utm +zone=? +datum=WGS84 +units=m +no_defs +geoidgrids=?" -t_srs "+proj=utm +zone=? +ellps=WGS84 +datum=WGS84 +units=m +no_defs"

    Las Vegas, NV

    Data for differencing
    Compare dataset: Las Vegas 2010 from the USGS 3DEP NV LasVegasValley 2010
    Reference dataset: Las Vegas 2018 from the USGS LPC NV LasVegas QL1 2016 LAS 2018
    2012A conus geoid available from NOAA

    Activity 3: Challenge- Vertical differencing with data with incorrect or incomplete metadata

    Vertical differencing of datasets with wrong metadata- Based on the metadata, are the datasets be ready to be differenced? Are the results what you expect? How can you improve the results?

    Outer Banks, NC

    Data for differencing
    Compare dataset: Outer Banks, NC, 2006 from the North Carolina Coast: Quantifying Patterns of Coastal Change (June 2006)
    Reference dataset: Outer Banks, NC, 2007 from the North Carolina Coast: Quantifying Patterns of Coastal Change (July 2007)
    2003 conus geoid available from NOAA