Accuracy of Structure-from-Motion derived digital elevation models and species-specific correction methods
This study will investigate
the accuracy of DEMs of salt marshes developed using a UAS and SfM techniques. The accuracy of these DEMs will be evaluated using real-time kinematic (RTK) elevation field measurements. Methods for correcting DEMs will be produced using vegetation species-specific correction factors.
About the Project
An important component of coastal conservation and restoration projects is the monitoring of multiple ecosystem parameters in the project area. This monitoring allows project managers to create project-specific designs and determine progress towards reaching project goals. The parameters monitored include but are not limited to elevation, shoreline position, and vegetation distribution. Monitoring parameters like this often requires intensive fine-scale field measurements. For example, plant growth and productivity will vary within small changes of elevation. Intensive fine-scale field monitoring efforts are frequently weakened by financial and workforce limitations.
The recent introduction of the unmanned aerial system (UAS) has removed previous limitations allowing coastal researchers to capture data on both fine-scale temporal and large-scale spatial resolutions. This technology allows for the capture of georeferenced images that can be processed into georeferenced maps. Post processing procedures then allow for measurements of multiple environmental parameters. Coastal managers have used UASs to estimate parameters including shoreline elevation, shoreline position, and vegetation coverage.
For example, it is possible to produce fine scale digital elevation models (DEMs) using LIDAR or Structure-from-Motion (SfM) techniques. These DEMs have increased in popularity due to their usefulness to inform modeling and planning efforts for marsh sustainability in relation to climate change and sea-level rise.
The introduction of UASs have allowed researchers to increase data collection while decreasing costs but they still have their limitations.
For example, marsh vegetation is known to introduce error when determining surface elevation values. Previous studies have focused on determining the error associated with LIDAR derived DEMs and developing correction methods. However, LIDAR technology can be expensive and require significant technical expertise.
Structure-from-Motion technology presents a more accessible alternative to LIDAR. The combination of SfM technology and UASs allows researchers to capture high accuracy data at a reasonable cost. With increased accessibility, these tools have become increasingly popular in ecosystem monitoring. However, SfM technology does have some of the same issues as LIDAR technology when attempting to develop DEMs. SfM derived DEMs can overestimate elevation in areas with dense and tall vegetation. However, no correction methods have been tested on DEMs produced using SfM techniques.
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Matt Virden, Extension Associate
