SURVEY NOTES

How Green Lasers are Illuminating the Underwater Secrets of Great Salt Lake

by Emily Kleber and Michael Vanden Berg

Bathymetric lidar data coverage of GSL.

Great Salt Lake (GSL) has a unique natural ecosystem, from birds to brine shrimp, and wetlands to open water. The lake also hosts a bustling extractive minerals industry and provides numerous recreational opportunities. Recently, the lake has reached historic lows, posing threats to the delicate ecosystem, industries, and surrounding communities. Understanding the impacts of changing lake levels requires accurate modeling of lakebed exposure and changing water volumes. This detailed understanding of the shape of the lakebed (or bathymetry) is invaluable to researchers studying its ecology, hydrology, and natural resources.

GSL is shaped more like a pan than a bowl. Given the low gradients (or slopes) of the lake bottom, one foot of lake elevation change can move shorelines by miles. Existing bathymetric data for the lake was collected in the late 1990s with sound-based sonar equipment towed behind a boat. Though high tech at the time, this method had several limitations that reduced accuracy, especially for natural features in the shallow waters. But what if you could use lasers instead of sonar?

Enter lidar, “light detection and ranging,” or in other words, shooting lasers at the Earth. Terrestrial, or land-based, lidar uses an aircraft-mounted sensor with a near-infrared laser (1064 nanometers [nm] wavelength). As the aircraft flies in a lawnmowing-like pattern, the sensor sends millions of light pulses towards the ground where they bounce off dry land before returning to the aircraft, generating a high-resolution representation of Earth’s surface. In contrast, bathymetric lidar systems use a visible green laser pulse (532 nm wavelength) to pierce the water’s surface, pass through the water column, bounce off the floor of a water body, and reflect back to the sensor. This reflected data is then processed to create a “point cloud” of tens of millions of elevation points depicting the shape of the lake bottom, shoreline, and playa, both above and below the water.

Collecting and processing bathymetric lidar data has unique technical and logistical challenges and can be impacted by factors including:

• Water clarity – GSL is notorious for having murky water, and water clarity impacts how deep the laser pulses can reach. Data acquisition during windows of water clarity is best (e.g., in early summer).
• Water depth – The deepest part of the lake is about 25–28 feet deep, depending on lake level elevation. It is difficult for the laser to penetrate to these depths especially if the water clarity is poor due to suspended sediment and/or biological activity.
• Weather – Good data collection requires a window of clear weather, mostly calm water, and specific sunlight angles. However, mirror-glass water often results in most light being reflected off the surface rather than penetrating to the lake bottom.
• Lakebed substrate – The laser pulses do not reflect well off soft substrates (e.g., mud) and dark materials that can absorb the laser pulse.
• Large area – The lake is very large, nearly 1,700 mi², making data acquisition expensive and difficult to manage. Also, processing massive amounts of data (i.e., petabytes!) can be challenging.

High-resolution bathymetric lidar data from an area about 2 miles west of northern Antelope Island. Several unique features are highlighted including large-scale desiccation-related polygons with microbialite domes growing along the perimeters, as well as newly discovered large-scale mounds interpreted to possibly be related to groundwater springs.

Since 2022, the Utah Geological Survey (UGS) has been leading an innovative effort to assess how well bathymetric lidar data collection could work at GSL, particularly in the south arm. Bathymetric lidar is a technology that has been around for decades but mostly used in marine, freshwater lakes, and river environments. To our knowledge, UGS’s efforts are the first time a high-elevation saline lake has been scanned using this technology. In partnership with the Utah Division of Forestry, Fire and State Lands, the UGS commissioned industry-leading specialists Aero-Graphics Inc. (a local Utah-based geospatial company) and Dewberry Inc. (a large international company with unique expertise in bathymetric lidar data collection) to collect bathymetric lidar data around the lake.

We started the project with a test area to develop best practices with this technology in a unique environment like GSL. The pilot study began in spring 2023 with a 50-square-mile area on the west side of Antelope Island, using an industry standard bathymetric lidar sensor (this data was collected by NV5 Geospatial). Overall, this survey obtained bottom returns over only 28% of the total area surveyed. In the deeper lake areas to the west (greater than 9 feet in water depth) bottom returns were not reliably detected. However, where data was recovered in the shallow shelf environment (depths less than 9 feet), the survey showed unprecedented high-resolution topographic detail, highlighting structures including microbialite reefs and possibly newly discovered spring-related carbonate mounds.

In fall of 2024, more reconnaissance data was collected along single flight paths using a much more powerful sensor. This sensor achieved bottom returns in water depths of up to 15 feet in the south arm but was only able to return data from depths less than 1.5 feet in the murkier north arm. Overall, the pilot study and lake transects provided important parameters for optimal data collection that maximized data quality and helped establish a budget for future surveys.

Elevation profile showing spread of bathymetric points from the lidar survey. Green laser pulses from the airplane-mounted sensor need to pass through the water surface and water column before potentially hitting and reflecting off the lake bottom. The number of lake bottom points (orange) decreases with depth.

Taking advantage of the annual clear water window in spring 2025, Aero-Graphics and Dewberry started whole-sale data collection over nearly 400 square miles of the south arm, focusing on the important shallow shelf area around the perimeter of the lake. The project team also collected data over three wetland areas east of the lake. Due to the poor data quality from our test flights over the north arm, further data collection in this area was deemed wasteful. The massive amount of data collected across the lake is currently being processed and full data delivery is scheduled for summer 2026. However, the pilot data is currently available, and we have already received some sneak peaks of the amazing new data.

Early analysis of some of the new bathymetry data is already providing key insights to researchers at the UGS. We found that this new data can be used to much more accurately model lake water elevation, lakebed exposure, and changing water volumes. In addition, the high-resolution data in the shallow water areas will significantly improve our understanding of the spatial distribution of GSL’s unique microbialite reefs, and the impacts of low lakes levels and exposure on these important structures, which are recognized as the base of the lake’s food web and ecosystem (see Survey Notes, v. 54, no. 1).

The new bathymetric lidar data can be used to create more accurate, higher-resolution lakebed elevation contours in the nearshore environment (multi-colored lines) compared to currently published data (black lines). In fact, the resolution is so high that the contours (in purple – 4191 feet) trace around individual microbialite domes that have 0.5 to 1.0 feet of relief.

Bathymetric lidar data can provide a glimpse into the secret hidden world of GSL. The challenges of data collection are immense, and although the technology does not work well in all areas of the lake, the data that is being returned will provide a level of detail about the lakebed never seen before. The UGS is excited to complete this study and share this new data with everyone that studies GSL and its changing environment.