Communications of the ACM
Drones Could Be Key Piece of Future Thunderstorm Prediction Process
Researchers are using I-wing configuration drones because they are steadier and can handle some weather-related adversity better than quad-copter drone.
Credit: University of Colorado Boulder
For nearly two hours in 1996, Bill Paxton and Helen Hunt tried desperately to place their weather-sensing equipment close enough to a tornado for it to be sucked inside the beast in order to study its behavior. Only when that instrumentation was anchored to the back of a pickup truck and driven through a cornfield into the path of the tornado did it actually work.
Such is the danger for atmospheric scientists trying to study storms — they have to be incredibly close with their instruments, but that proximity poses an imminent threat to human life. As of yet, no method of closing distance between storm and storm chaser has proven effective and safe at the same time.
However, through the use of drone technology, a Texas Tech University researcher and his colleagues in the Midwest may be close to a solution.
Chris Weiss, an associate professor in the Department of Geosciences, is partnering with researchers from the University of Colorado and the University of Nebraska to study how temperature, humidity, and other atmospheric factors affect the development of thunderstorms. Funded by a grant from the U.S. National Science Foundation, the group hopes to sample severe storms to better predict specific hazards, such as tornadoes, in hopes of saving human lives.
To do that, part of their research will involve flying Unmanned Aerial Vehicles (UAVs) in as close proximity to developing thunderstorms as possible, then taking readings on factors such as humidity and temperature to see if there is a predictable correlation to storm severity.
"That is what this is really about, using a nimble platform to obtain measurements in specific portions of the storm and areas in the environment around the storm that helps us better predict the phenomena that can occur," Weiss says.
Predicting the Unpredictable
Before the team can fly drones into an area of thunderstorm development, they have to determine just how close they can get.
Not only is the threat from tornados prominent, but other factors like hail and high winds could damage the UAV if it gets too close. Therefore, researchers are developing mathematical models that will determine, at least to begin with, how close they can safely fly the drones to the thunderstorm.
The second part of those mathematical models is determining from where in the thunderstorm samples need to be taken. Is it from behind or in front of the storm, or somewhere on the sides? Weiss says the team will attempt to avoid the forward flank region of the storm, as that area is just downwind of the updraft where the heaviest rain and hail are produced.
"Our focus is getting more on the periphery of that part of the storm, but if we have success with that, we will certainly be willing to take a few risks," Weiss says. "How can I use this model and the information from it to identify where in the storm needs to be sampled to improve the prediction of a specific hazard? That is where the UAV comes in."
Because of the nature of the research, a quad-copter style of UAV would not be sufficient. Researchers need something that is steadier and can handle at least some weather-related adversity. That is why they are using the I-wing configuration of drones, which look more like a regular aircraft.
Weiss says this type of aircraft has been used in prior weather-related experiments and "can take a fair amount of abuse."
"We need a platform that is adaptable, a platform that can move quickly, is nimble, and is not constrained by a road network like vehicle-borne instrumentation," Weiss says.
Of course, there are restrictions, just as there are with flying any UAV. The altitude limit for a UAV of this configuration is 1,000 feet, which will limit readings. Researchers must also follow all other U.S. Federal Aviation Administration rules and guidelines concerning drone operation.
Weiss says, however, the regulations are not as restrictive as they have been in the past, which has opened this area of research for more investigation. Currently, in Alabama, a project called the Verification of Rotation in Tornadoes Experiment (VORTEX) uses UAVs to study tornadic rotation and development.
Storm Sampling
But, Weiss says, as far as he knows, his group's research will be the first to use a combination of drones, ground-based instrumentation, and mobile radar instrumentation to get a demonstration of storm sampling to improve forecasts.
"Based on a review we received on the proposal and my read on how this has been done before, this is really a novel concept to combine in situ observation and radar observation at the surface and aloft with these unmanned aircraft," Weiss says. "I think the NSF recognized this as kind of a unique opportunity to gain an unprecedented type of observation that can help improve our forecasting."
While Colorado owns the UAVs that will be used in the experiment, two Ka-band mobile Doppler radars from Texas Tech will play a crucial role. Nebraska will contribute with its vehicle-based platforms.
Once the mathematical models have been established, the next step will be a demonstration of the research in what Weiss calls a "shakeout mission" of short duration to see if the ideas can work on a small scale. That, he says, is planned for next summer somewhere in Colorado, as conditions in July and August will be more favorable for severe storms in Colorado than they will be in Texas.
Then, in 2018, the grant calls for a full demonstration of the experiment, which means the research team will have to chase down the thunderstorms instead of letting storms come to them.
"That will involve a week or two of storm chasing where we try to demonstrate the capabilities of our system," Weiss says. "We call it the Holy Grail of adaptive sampling, where you have a severe storm and the numerical models you run in the field concurrently represent the storm. That is a challenge in itself, and using that model to inform the UAV to run around to the backside of the storm and sample relative humidity at, say, 300 meters off the ground."
If the FAA gives the OK, a drone could fly higher near a storm, as the vertical dimension has largely been undersampled in previous field campaigns. Currently, that can only be studied using weather balloons, which are effective but are susceptible to winds that can force the balloon to travel at an angle instead of ascending straight up.
If all goes to plan, this project could be just the first step toward improving storm prediction methods using UAVs. Weiss says he would like to see continued investigation, particularly into the development of storms along the dryline, an area that affects this region of the United States.
"We're terrible at figuring out where exactly thunderstorms will develop, specifically along the dryline," Weiss says. "We don't have a good handle on where that happens. What we believe is by uncovering the finer scales of observation, how temperature and humidity vary along the dryline, it can help us predict where the thunderstorms will develop. That is a real straightforward application of drone technology and something that can be easily accomplished with the resources we have now, and we plan to propose that. I think that is the next step."
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