Scientists Developing Drone-Carried Lidar for Nautical Charting

Today, when scientists map the ocean floor, they use large, heavy bathymetric lidar carried by manned aircraft to capture data, which is then processed after the fact. A group of Georgia Tech Research Institute scientists believe they can speed up the mapping process with a miniaturized lidar system currently undergoing testing, said Grady Tuell, principle research scientist for the project.

Georgia Tech has developed a 250-pound lidar system capable of transmitting data in real time and that can be carried by a medium-sized unmanned aircraft such as the MQ-8 Fire Scout helicopter, he said. Most existing systems weigh upwards of 600 pounds.

“We hope to finish what we’re calling our Mark 1 system by late summer of 2015,” he said. This version would be deployed on a drone, but “it would not necessarily be ruggedized.”

For decades, the Navy has used bathymetric lidar to create nautical charts or detect submarines moving through the oceans, Tuell said. They fire lasers into the water column and measure the depth of the water based on how long it takes for a signal to return.

However, light scatters and bends underwater, and other signals in the sea can cause interference, so it is difficult to compute the accuracy of each data point collected. To tackle this issue, the team developed a technique called “total propagated uncertainty” to estimate accuracy using navigation, distance and refraction angle measurements, according to information from Georgia Tech.

The result is a lidar that can both process data and predict the quality of that information in real time, Tuell said.

The Georgia Tech team has finished the design of the lidar system and is currently testing the accuracy of its components, he said. In the spring, it will demonstrate the scanner’s ability to map the bottom of a water tank at the campus.

Commercial off-the-shelf lasers, lenses and detectors were used to build the system, but the team had to purpose-build the algorithms, software, telescope and optics as well as integrate all of the pieces,” Tuell said.

To cut size and weight, they developed a lighter scanner and telescope. Instead of using a reflective telescope, which is common in bathymetric lidar, they designed a catadioptric telescope that uses mirrors and lenses to reflect and refract light.

Such telescopes “fold the light path many, many times,” Tuell said. “That allows you to reduce the length of the tube down considerably, by 75 percent perhaps.”

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