Sandia Lab uses fog chamber to optically test novel sensors

23 Nov 2021

Aim of dedicated test facility is to ensure safe performance of future transportation systems.

Fog can make travel by water, air and land hazardous when it becomes hard for both people and sensors to detect objects. Researchers at Sandia National Laboratories’s fog facility are addressing that challenge through new optical research in computational imaging and by partnering with NASA researchers working on Advanced Air Mobility, Teledyne Flir and others to test sensors in customized fog that can be measured and repeatedly produced on demand.

“It’s important to improve optical sensors to better perceive and identify objects through fog to protect human life, prevent property damage and enable new technologies and capabilities,” commented Jeremy Wright, optical engineer.

Built in 2014, Sandia’s fog chamber measures 55m x 3m x 3m (180 ft x 10 ft x 10 ft). The chamber is lined with plastic sheeting to entrap the fog.

When the team begins a test, 64 nozzles spray a custom mixture of water and salt. As the spray spreads, the humidity builds and thick fog forms. Soon, an observer inside won’t be able to see the walls, ceiling or entrance through the aerosol and people and nearby objects will be obscured or completely hidden.

Researchers from NASA’s Ames Research Center have visited Sandia to perform a series of experiments to test how commercially available sensors perceive obstacles in fog. The Revolutionary Aviation Mobility group is part of the NASA Transformational Tools and Technologies project.

All-weather testing

“We tested perception technologies that might go into autonomous air vehicles,” said Nick Cramer, the lead NASA engineer for this project. “We want to make sure these vehicles are able to operate safely in our airspace. This technology will replace a pilot’s eyes, and we need to be able to do that in all types of weather.”

The team set up a stationary drone in the chamber as a target and then tested various sensors to see how well they could perceive the drone in the fog. “The fog chamber at Sandia National Laboratories is important for this test,” said Cramer. “It allows us to really tune in the parameters and look at variations over long distances. We can replicate long distances and various types of fog that are relevant to the aerospace environment.”

Cramer said one of the challenges of self-flying technology (drones) is that there can be many small vehicles flying in close proximity. “We need to be able to detect and avoid these small vehicles. The results of these tests will allow us to dig into what the current gaps in perception technology are to moving to autonomous vehicles.”

Camera developer Teledyne FLIR has tested its infrared cameras at Sandia’s fog facility to determine how well they detect and classify pedestrians and other objects. Chris Posch, engineering director, automotive, for Teledyne FLIR, said the cameras could be used to improve both the safety of today’s vehicles with advanced driver-assisted systems features such as automatic emergency breaking and autonomous vehicles of the future.

“Fog testing is very difficult to do in nature because it is so fleeting and there are many inherent differences typically seen in water droplet sizes, consistency and repeatability of fog or mist,” said Posch. “As the Sandia fog facility can repeatedly create fog with various water content and size, the facility was critical in gathering the test data in a thorough scientific manner.”

New research

A team of Sandia researchers recently published a paper in Optics Express describing the latest results from a three-year project to use computational imaging and the science behind how light propagates and scatters in fog to create algorithms that enable sensors to detect, locate and image objects in fog.

“Current methods to see through fog and with scattered light are costly and can be limited,” said Brian Bentz, electrical engineer and project lead. “We are using what we know about how light propagates and scatters in fog to improve sensing and situational awareness capabilities.”

Bentz said the team has modeled how light propagates through fog to an object and to a detector – usually a pixel in a camera – and then inverted that model (as published on SPIE Digital Library) to estimate where the light came from and characteristics of the object.

Bentz says the team has used the model to detect, locate and characterize objects in fog and will be working on imaging objects during the project’s final year. The team has been using Sandia’s fog facility for experimental validations. Parallel to this research, the Sandia team created two bench-top fog chambers to support a project at academic alliance partner, West Lafayette, Indiana-based Purdue University.

Sandia is studying and characterizing the fog generated by its new bench-top fog chamber, while Purdue is using its twin system to perform experiments. Purdue professor Kevin Webb is leading research to develop an imaging technology based on how light interferes with itself when it scatters and using those effects to detect objects.