Airborne LIDAR for Clear Air Turbulence Detection
Every pilot who has experienced severe Clear Air Turbulence (CAT) would like to hear the news that alerts will no longer need to come from other pilots in the area, but from accurate onboard turbulence detection systems. Though this is still a ways off, detection systems moved another step forward within the last two years, thanks to a feasibility study on Light Detection and Ranging (LIDAR) that piggybacks onto the previous work of RTCA SC-230: Airborne Weather Detection Systems.
In 2018, the Japan Aerospace Exploration Agency (JAXA) and Mitsubishi approached the FAA requesting information on how to get the LIDAR detection system they had flown as a prototype in a Boeing aircraft approved for use in the U.S. As no specific regulations yet existed, the FAA came to RTCA to inquire about developing Minimum Operational Performance Standards (MOPS). SC-230 took FAAs inquiry to the PMC with a proposal to conduct a feasibility report as the new technology was determined not to be ready yet for the process of developing MOPS.
“We had already completed the first RTCA Feasibility Study in 2017 (AFS-1: Feasibility Study Weather Radar for Ice Crystal Detection), so we had a good idea on an approach,” said Venkata “Ven” Sishtla of Collins Aerospace. “A couple of folks from Mitsubishi came to Cedar Rapids (Collins) and we did an extensive white board session to kick it off, with help from my Co-Chair on WG-11, Shumpei Kameyama.”
The presentation to Collins looked through various aspects of LIDAR technology with the goal to be able to detect clear air turbulence to 12 Nautical Miles (12NM) in front of an aircraft. It further looked to determine realistic goals for an airborne LIDAR system when used for clear air turbulence detection, aircraft manufacturer needs for an airborne LIDAR clear air detection function and the feasibility that LIDAR systems can meet aircraft manufacturer needs.
“We wanted to look at what Original Equipment Manufacturers (OEM’s) want, what are the capabilities of LIDAR independent of OEM’s needs, and how can capabilities of LIDAR meet OEM 12NM detection for OEM. Was the technology there or not?” said Sishtla.
The report details a study performed to assess the maturity and the feasibility of using an airborne LIDAR system for detection of clear air turbulence (CAT). The study’s intended function was to consider situational display of regions ahead of the aircraft that presented potential hazards to the aircraft due to CAT. The report reveals Coherent LIDAR using current technology is not capable of meeting OEM goals for CAT. The report also reveals that direct detection LIDAR is capable of meeting the OEM goal but more research is needed to substantiate this conclusion.
Still needed as this new technology advances are simulation studies, additional data collection, research for use of LIDAR for precision altitude measurement and further research, and eventually MOPS, for coupling LIDAR to flight control systems for gust load alleviation.
“As a weather radar engineer, it was extremely enlightening,” said Sishtla. “We hope that as technology develops, that there is a chance for sensor detecting clear air turbulence. With Direct Detect, we only have equations on paper, and we’d want simulation and flight tests, similar to what was done for the ice detection feasibility study.”
Joining RTCA, FAA, Collins, JAXA and Mitsubishi to collaborate on this challenge were other members of WG-11, including representatives from Embraer (Brazil), Airbus (France), the DLR Institute of Atmospheric Physics (Germany) and SC-230 Co-Chairmen Dawn Gidner (from Honeywell) and Jeff Finley (from Collins Aerospace).
“I’m proud of this amazing team that came together and said, ‘let’s see what we can do with this real-world problem,’” said Sishtla. “It’s definitely a promising field in desperate need of a solution.”