Topobathy Lidar 101
Maddi McArthur, Joy L, Erin Dawn Trochim
This blog post is the first in a series that will explore topobathy data ethics, case studies utilizing this data, and highlight other geospatial tools. Keep an eye out for them!
Topobathymetric lidar (or “topobathy lidar” for short) is a geospatial technology used to map both the land and seafloor. It offers a comprehensive view of coastal and nearshore terrain that is immensely useful for coastal management. This blog post will delve into the basics of how topobathy lidar works, its applications, and where you can access this data.
What is Topobathy Lidar?
Lidar, which stands for light detection and ranging, uses light pulses to detect and map landscapes. These light pulses are fired from a scanner towards the earth’s surface, bouncing back once they hit an object. By measuring the time it takes for the pulses to return, the lidar system can calculate distances with incredible precision. Topobathymetric lidar is unique because it utilizes two lasers, a near infrared laser and a visible green laser. All lidar systems use a near infrared laser to map non-submerged landscapes and detect water surfaces. The visible green laser is unique to topobathy lidar, as it is used to see beneath the water to measure submerged land. This is where the name “topobathymetric” comes from, where the “topo” is short for topography (land surface) and bathy stands for bathymetry (submerged land).
Topobathy lidar data is collected aerially, by plane or by UAV, allowing detailed data to be collected over the landscape and seascape. Although lidar lasers collect highly detailed data, they’re really only able to detect features that are absolutely still, like vegetation, human structures, and parked vehicles. Once the lidar laser collects the data points, software and human processors filter through it to create a 3D model of the scanned environment. You can see an example of this in the image below. Topobathy lidar data can be used in its original point cloud form, or as a 1-meter resolution gridded product.
Applications of topobathymetric lidar data
Topobathy lidar provides information for numerous coastal uses, which facilitates informed decision-making for coastal zone management and resilience planning. For example, it is essential that topographic and bathymetric information is available to aid the development and maintenance of marine infrastructure. Topobathy lidar data provides detailed elevation models, up to one meter in resolution (see image set below), aiding in the design and upkeep of bridges, ports, and offshore structures.
Coastal regions are also highly susceptible to environmental changes and natural disasters. In the aftermath of natural disasters like hurricanes and tsunamis, topobathy lidar surveys can facilitate a quick damage assessment of coastal and underwater terrain which is crucial for effective disaster response. Topobathy lidar data can also aid in assessing flood risk, mapping habitats, and monitoring coastal erosion and sea-level rise.
Limitations of topobathy lidar
Like all types of data, topobathy lidar has its drawbacks. Lidar equipment is costly, and it is also expensive to fly a plane to collect topobathy data. Expertise is required to operate equipment and process the data. Processing and interpreting this data is also time-consuming and computationally intensive. These factors limit the accessibility of topobathy lidar data collection. Additionally, even though collecting topography data with an infrared laser is a fairly straightforward process, the green laser that collects bathymetry data requires ideal conditions to “see” properly. When high winds cause waters to be choppy, laser pulses can get reflected or refracted by the waves which leads to inaccurate depth measurements. Similarly, it can be nearly impossible to accurately map the seafloor if the water is highly turbid (full of sediment) because the extra particles in the water scatter the laser pulses. Careful timing of data collection to minimize these environmental issues is vital to making a topobathymetric lidar survey worthwhile. Additionally, it is not necessary to entirely rely on topobathy lidar data to have a strong understanding of coastal terrain. Other geospatial tools like sonar or satellite data can be layered together with topobathy data to create a more comprehensive picture of a coastal environment.
Where to find the data
Numerous agencies, including the U.S. Army Corps of Engineers (USACE), United States Geological Survey (USGS), and National Oceanic and Atmospheric Administration (NOAA), collect open-source topobathy lidar data throughout US coastal regions. Much of the data collected by these organizations and others is available on NOAA’s Digital Coast. This repository allows users to search for topobathy data by year, area, data provider, elevation product, projection, datum, and format. Users can download these data as point clouds, digital elevation models, and contours.
In conclusion, topobathy lidar is a powerful tool for a variety of coastal management applications. It provides a holistic view of coastal and nearshore terrain that is essential for building and maintaining marine infrastructure, assessing flood risk, mapping habitats, monitoring coastal erosion and sea-level rise, and responding to natural disasters. Although the technology does face challenges, careful data collection planning and utilization of other geospatial resources can help overcome them. The availability of topobathy lidar data from various agencies, including open-source repositories like NOAA’s Digital Coast, improves its accessibility to anyone who may want to utilize it. Continued collection and dissemination of this data is key to supporting resilient coastal communities and improving our understanding of dynamic coastal environments.
