By Chelsea Scott
OpenTopography is happy to announce the release of a new vertical differencing tool for performing change detection of multitemporal topography data. This release is the latest in a growing set of tools developed by OpenTopography for measuring natural and anthropogenic surface change with high resolution topography. We now have enabled on-demand differencing of point cloud and raster data for over 50 dataset pairs that show processes including urban growth, vegetation change, landslides, earthquakes, volcanic eruptions, and sand dune migration.
The new vertical differencing tool begins with raster topography datasets and performs the differencing by regridding both datasets to identical grids. The new tool works more efficiently and over larger datasets than the older variant that began with the point cloud dataset. We have also implemented differencing between Digital Terrain Models (DTMs) and Digital Surface Models (DSMs) acquired in different surveys.
Here are several examples from the new differencing tool:
2019 Ridgecrest, California, Earthquake: The magnitude-7.1 Ridgecrest earthquake occurred on July 5, 2019 in the desert of southeastern California. The mainshock ruptured a northwestern oriented fault. The surface rupture stretches diagonally across the image below where there is a sharp almost linear change in the vertical difference. The red and blue colors in the mountains are artifacts that represent the horizontal shift of topography during the earthquake. Scientists use these differencing products to map the ruptured fault and measure the fault offset at the Earth's surface during the earthquake. Perform Ridgecrest Earthquake differencing here.
Vertical differencing of the 2019 magnitude-7.1 Ridgecrest Earthquake in California from the 2019 pre-earthquake topography from a stereogrammetric DEM and the 2019 post-earthquake lidar topography.
2018 Kilauea, Hawaii, Eruption: In the spring and summer of 2018, the Kilauea Volcano erupted along the southeastern coast of the island of Hawaii. This shield volcano produced extensive lava flows and fountains in its largest eruption in at least 200 years. The red colors represent the collapse of the volcano’s caldera. This happens as the magma chamber empties, causing the roof to collapse. This map of change helps volcanologists to estimate the amount of erupted lava and the behavior of the volcanic system beneath the surface. Perform differencing for the Kilauea eruption here.
Differencing of the 2018 Kilauea eruption in Hawaii. The differenced datasets are the June and July 2018 Kilauea topography.
Vegetation Change in Central Pennsylvania: This shows the difference between the Digital Surface Model (DSM) for the summer leaf-on dataset and the Digital Terrain Model (DTM) for the winter leaf-off dataset at the Susquehanna Shale Hills Critical Zone Observatory. The blue colors represent the height of vegetation in the summer, highlighting the farms in the valley (center of image) and the dense forests along the ridge (top left). These results are used to measure the height of trees and monitor forest health. Perform differencing at Susquehanna Shale Hills (See DTM and DSM options in Panel 3).
Susquehanna Shale Hills Critical Zone Observatory in Central Pennsylvania: Differencing the July 2010 leaf-on Digital Surface Model (DSM) and the December 2010 leaf-off Digital Terrain Model (DTM).
New User-Interface: Frequent users of the differencing tools are likely to notice that the user-interface has changed. After a user selects differencing for a particular dataset, they are taken to this page that shows the differencing options available for the selected dataset and a brief description of the different tools. The user should select the tool that is most appropriate for their dataset and interest.
New differencing user interface.