Volcano Watch: First light — and flight — for Hawaiian Volcano Observatory’s new airborne lidar system

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. Today’s article is written by Hawaiian Volcano Observatory geologist and geographic information system specialist Mike Zoeller.

Topographic mapping has been a key component of volcano monitoring for decades, helping scientists study morphologic changes and predict the paths of lava flows during eruptions.

Lidar systems are a preferred mapping tool, and the U.S. Geological Survey Hawaiian Volcano Observatory on the Big Island now has a lidar system of its own to generate mapping products more frequently than ever before.

Lidar — short for light detection and ranging — has become preferred for mapping because of the precision of its measurements and fine-scale resolution of its data products.

The systems operate by emitting many thousands of laser pulses per second, then recording the precise return times of the light waves after reflecting off different features in three-dimensional space.

On Hawaiian volcanoes, these features are usually the surfaces of lava flows.

The return times are used to automatically calculate distances to those features, providing their X, Y and Z coordinates when the instrument’s position is precisely known.

Compiling all the individual measurements results in a “point cloud” depicting the surveyed area.

For more than 15 years, lidar systems have been used intermittently at Kīlauea and Mauna Loa volcanoes, including aerial systems such as one contracted in 2019 by the Hawaiian Volcano Observatory for a survey of Kīlauea, as well as ground-based terrestrial systems such as the one the obsveratory borrowed from the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory from 2021-23 for surveys of Kīlauea’s Halemaʻumaʻu Crater.

Both system types require a global positioning system to record their position during the survey, but aerial systems also require a high-precision inertial measurement unit to track directional roll, pitch and yaw.

These parameters are used for minute corrections of the instrument’s position and orientation, allowing the measured features to correctly locate in the point cloud.

Lidar systems are complex, and therefore expensive, so prior surveys on Hawaiʻi Island could only be conducted when permitted by the availability of funding and/or collaborators.

That changed with passage of the Additional Supplemental Appropriations for Disaster Relief Act of 2019 by U.S. Congress, providing the Hawaiian Volcano Observatory with funds to purchase a lidar system, among other upgrades, in the aftermath of the 2018 Kīlauea eruption.

The observatory used the funds in April 2022 to purchase a Riegl VUX-120 airborne lidar system, which is mountable to a helicopter and enabling surveys of more expansive areas than a terrestrial system.

The instrument arrived unoperational in November 2022. Using the VUX-120 required building a mount to attach it to the observatory’s contracted helicopter and integrating the system with a control computer and other accessories.

The University of Hawaiʻi at Hilo’s Spatial Data Analysis and Visualization Lab provided a template design for a helicopter mount.

The Hawaiian Volcano Observatory again leaned on their collaborators at the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory — who made various lidar systems of their own operational, including another VUX-120 — for the lidar’s integration.

The setup work was completed this past August.

A Cold Regions Research and Engineering Laboratory technician visited the observatory in early September to teach staff how to use the VUX-120 and assist during its first operation.

The system successfully completed a ground test Sept. 2 at the observatory’s warehouse in Hawaiʻi Volcanoes National Park, followed by its first flight Sept. 5 aboard the contracted helicopter.

The Hawaiian Volcano Observatory decided to survey the vicinity of the June 3 Kīlauea Southwest Rift Zone eruption for the lidar’s first flight, which was a resounding success.

Data were captured at a density of about 60 points per square yard, enabling the construction of a high-accuracy digital elevation model of the June 3 eruption vicinity.

Some lessons were learned to further improve data quality in the future, which is especially important when the resulting digital elevation models might be used for critical assessments of volcanic hazards.

The observatory continues to rely on photographic surveys for rapid-response mapping of topography during eruptions, but the VUX-120 will provide more definitive datasets when time allows for its slightly longer-duration surveys, which were not possible during the recent brief Kīlauea middle East Rift Zone eruption.

To our knowledge, this is the only helicopter-mounted lidar system operated by anyone in the U.S. Geological Survey, so there might be opportunities to use it elsewhere in support of hazard assessments and scientific research.

The Hawaiian Volcano Observatory sincerely thanks the UH-Hilo Spatial Data Analysis and Visualization Lab and U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory teams for their support while we take our first steps into the world of airborne lidar, and we look forward to future collaboration.

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Volcano Activity Updates

Kīlauea is not erupting. Its USGS Volcano Alert level is at Advisory.

While the Sept. 15-20 middle East Rift Zone eruption ended, unrest continues at a low level in this region of Kīlauea.

During the past week, about 60 earthquakes were located in the Kīlauea summit region and about 50 in the upper-to-middle East Rift Zone area.

Ground deformation rates have greatly decreased since the eruption, but data show that magma is continuing to move at a low rate from the summit to the middle East Rift Zone. Future intrusive episodes and eruptions could occur with continued magma supply.

The most recent measurement of sulfur dioxide (SO2) emission rate at the summit was 60 tonnes per day on Sept. 17, and SO2 emissions were not detected downwind from the eruption site on Monday, Sept. 23.

Mauna Loa is not erupting. Its USGS Volcano Alert Level is at Normal.

No earthquakes were reported felt in the Hawaiian Islands during the past week.

The Hawaiian Volcano Observatory continues to closely monitor Kīlauea and Mauna Loa.

Visit the observatory’s website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.