Collecting geospatial data in Alaska is not for the faint of heart. The rugged terrain makes it dangerous and expensive to send people out in the field. The extreme weather leaves only limited windows of time to complete aerial surveys. Not to mention the challenges like rapid changes with freezes and thaws impact measurements on the coast, along rivers and over bodies of water.
In prepping for a recent acquisition project to fully characterize the subsurface river bottom in a glacial fed river in South Central Alaska, we knew we would have to address all of these challenges. Because the river was fed by a glacier, the acquisition needed to be done in early spring before the glacial melt introduced silt that would make bathymetric lidar useless in turbid water. The project spanned from coastal mud flats near sea level over heavily braided channels to the glacier feeding the river at an elevation of more than 4,000 feet. The rapid elevation, combined with rainy and cloudy weather, made it unsafe to do the acquisition via fixed-wing aircraft.
Multisensor Platform on Helicopter Saves Time
Since time was paramount for this project, we devised a plan that enabled our team to do the entire survey during the brief windows when weather cooperated. We used a helicopter equipped with multiple sensors for bathymetric data, lidar, thermal video and oblique photos. So instead of flying a fixed wing aircraft at 1,200 feet, the helicopter allowed us to fly under the clouds and closer to the river to collect better, more accurate data and images. The helicopter also offered greater maneuverability, enabling our crew to pivot and cover all the needed flight lines quickly and efficiently.
Having this multisensor platform affixed to a helicopter enabled us to do the entire acquisition in less than two days. We were able to quickly deploy our team when weather broke, during low tide before the glacial melt started. This approach saved the client time and money, and eliminated the need to send a large crew of ground surveyors to run hundreds of transects in a potentially dangerous river in remote Alaska.
By flying lower and slower with the helicopter, we were able to capture higher density lidar and greater imagery ground sampling distance (GSD), providing a high level of detail to our client. The data collected this spring will be merged into a larger topobathymetric lidar dataset we collected in 2022, which will contribute to a broader watershed analysis.