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March-April 2012

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UAVs: The New Frontier for Weather Research and Prediction

In mid-September 2005, just weeks after Hurricane Katrina wreaked destruction on New Orleans, Louisiana and other swaths of the Gulf Coast, Hurricane Ophelia tracked erratically off the Atlantic Seaboard of the United States, ultimately driving toward the Outer Banks of North Carolina. Ophelia, which vacillated in magnitude between a tropical storm and a hurricane, inflicted relatively little damage before drifting into the North Atlantic, the cold, enervating waters of which ultimately snuffed the life out of the system. While the storm lies in the shadow of Katrina in terms of property destruction and death toll, scientific history records Ophelia as the opening of a new chapter of meteorological exploration. During the peak of the storm's life, a lumbering four-engine WP3D Orion “hurricane hunting” aircraft of the Aircraft Operations Center of NOAA, packed with crew and scientists, penetrated Ophelia's core repeatedly, collecting a slew of data on each wing-and-fuselage-beating pass through the storm's rain bands and eyewall.

Although NOAA has been conducting these flights for years, they are never routine, and each is vitally important, as scientists use the data they provide to formulate and refine storm track prediction algorithms. During Ophelia's passage along the Atlantic Coast, however, another airplane dove into the heart of the storm—an odd looking craft with its engine and propeller below and to the rear of its wing, and an inverted “V” tail at the end of two skinny booms. It was an airplane called Aerosonde, built by the AAI company. Like the Orion, the Aerosonde collected gigabytes of data, including wind speed and direction, barometric pressure, and temperature. Unlike the girthy Orion, however, the Aerosonde has just one engine, a wing span one-tenth of that of the Orion, and most notably, the Aerosonde has no onboard pilot or crew. Ophelia's passage marked the first time an unmanned aircraft penetrated a cyclonic storm.

Unmanned aircraft—the wondercraft of the skies, which to many of us resemble giant robotic insects due to their bulbous noses and spindly wings—have until recently been used primarily for military applications. Today, unmanned (or more appropriately termed, unoccupied) aerial vehicles (UAVs) fly missions over agriculture fields so that farmers can monitor crop growth, aid in mineral exploration in inhospitable reaches of the globe, gather imagery for mapmaking in quickly evolving urban environments, and help search and rescue teams locate lost hikers, among an ever growing list of uses.

Caption: With smoke from the Lake Arrowhead area fires streaming in the background, NASA's Ikhana unmanned aircraft heads out on a Southern California wildfires imaging mission.

Caption: With smoke from the Lake Arrowhead area fires streaming in the background, NASA's Ikhana unmanned aircraft heads out on a Southern California wildfires imaging mission.

Dangerous Missions

UAVs are ideally suited for what engineers and practitioners call “3-D” missions, or those that are “dull, dirty, and/or dangerous.” Flying, by its very nature, is dangerous for humans, even in the most proven aircraft in dead calm conditions. Flying into hurricanes and tropical storms, regardless of the sturdiness of an airframe, is about as dangerous an activity as any that humans can undertake. Having a UAV like the Aerosonde, which during Ophelia beamed back measurements twice a second to scientists and operators safely on firm ground hundreds of miles away, mitigates any chance of danger to people involved in storm research. And with real-time transmission of data, even if the craft goes down, researchers at least have all measurements up to the moment the data transmitter in the aircraft fails.

During one of the WP-3D Orion flights into Ophelia, the crew explained that they typically don't fly the aircraft below 5,000 feet above sea level due to high winds lifting corrosive salt spray into the air—a decidedly dirty aspect of the mission, because salt spray ingested into one of the Orion's turboprop engines would require a complete rebuild if not thoroughly cleaned immediately after landing. However, some of the most important data to be gleaned from a cyclonic storm lie in its lowest reaches, the region where energy is transferred from warm sea water to the storm itself. This is exactly where the Aerosonde explored during its Ophelia flight, travelling at times just 500 feet above the roiling ocean while inside the storm. As NOAA noted after the flight, the Aerosonde provided “the first-ever detailed observations of the near-surface, high wind hurricane environment, an area often too dangerous for NOAA and U.S Air Force Reserve manned aircraft to observe directly.” Two years later, in November 2007, the Aerosonde flew inside Hurricane Noel for more than seven hours, flying as low as 300 feet in sustained winds of up to 80 miles per hour. The Noel flight marked the first time a UAV penetrated a full-fledged hurricane (Ophelia was a tropical storm when the Aerosonde flew into it).

In addition to flying into the lowest depths of cyclonic storms, UAVs are now flying into another realm where traditional atmospheric research aircraft cannot: above them, gaining imagery and data from long duration flights at altitudes of up to 65,000 feet. In August 2010, NASA's Global Hawk, equipped with an array of cameras and instruments, flew over Tropical Depression Frank in the Pacific Ocean—a mission lasting 15 hours. Although currently deployed weather satellites can already take images of storm systems from above, researchers can position the Global Hawk directly above a storm at will (as well as off to the side, for oblique images), and the UAV can measure atmospheric conditions near the storm in addition to gathering imagery, something that is impossible for a satellite in orbit above the earth's atmosphere. After Frank, NASA's Global Hawk flew over Hurricane Earl in the Atlantic (the first ever overflight of a hurricane by a UAV), followed by a mission over Hurricane Karl in the Gulf of Mexico, with the Karl flight lasting an incredible 25 hours. Because the Global Hawk, which has a wing span similar to that of a WP-3D Orion, does not have to accommodate humans onboard, its design maximizes endurance and cargo capacity, giving it a range of over 15,000 miles and flight times as long as 36-plus hours, with a service ceiling of 65,000 feet.

While not currently operational, Aero-vironment, one of the world's leading manufacturers of UAVs, is testing its Global Observer, a “stratospheric persistent” aircraft that the company foresees will be able to stay aloft for up to a week at a time at altitudes up to 65,000 feet, and carry up to 400 pounds of instruments. One of the stated missions for the liquid hydrogen-powered Global Observer is high-resolution tracking of hurricanes and other cyclonic storms; it should be able to stay above any one system for the majority of the storm's life, without a break. With data gleaned from both overflights of systems and from low-level flights through storms, scientists are able to not only better understand the dynamics of storms, but also to refine the accuracy of prediction models.

Caption: Maurice Gonella (left) and Ryan Vu of Aerosonde North America prepare the Aerosonde unmanned aerial vehicle (UAV) at the NASA Wallops Flight Facility, Wallops Island, Virginia, for flight into Tropical Storm Ophelia on September 16, 2005.

Caption: Maurice Gonella (left) and Ryan Vu of Aerosonde North America prepare the Aerosonde unmanned aerial vehicle (UAV) at the NASA Wallops Flight Facility, Wallops Island, Virginia, for flight into Tropical Storm Ophelia on September 16, 2005.

Caption: The Aerosonde unmanned aerial vehicle is released from its transport vehicle on the runway at the NASA Wallops flight Facility, Wallops Island, Virginia, to fly into and take measurements of Tropical Storm Ophelia.

Caption: The Aerosonde unmanned aerial vehicle is released from its transport vehicle on the runway at the NASA Wallops flight Facility, Wallops Island, Virginia, to fly into and take measurements of Tropical Storm Ophelia.

Caption: This photo of Tropical Storm Frank was taken from the HDVis camera on the underside of the Global Hawk aircraft on Saturday, August 28, 2010, at 5:07 pm EDT as the aircraft approached Frank for the second time. The Global Hawk captured this photo from an altitude of 60,000 feet (about 11.4 miles).

Caption: This photo of Tropical Storm Frank was taken from the HDVis camera on the underside of the Global Hawk aircraft on Saturday, August 28, 2010, at 5:07 pm EDT as the aircraft approached Frank for the second time. The Global Hawk captured this photo from an altitude of 60,000 feet (about 11.4 miles).

Caption: Global Hawk in flight for WISPAR research, Winter Storms and Pacific Atmospheric Rivers.

Caption: Global Hawk in flight for WISPAR research, Winter Storms and Pacific Atmospheric Rivers.

Is It a UAV? A UAS? A Drone? And Does the “U” Stand for Unmanned, Unoccupied, or Uninhabited?

One of the most confusing aspects of aircraft sans human crew is the field's nomenclature. Some call these aircraft “drones,” but other sources note that the term “drone” refers to a simple “program and forget” flight control system, where an aircraft simply flies on a basic course and then crashes (or gets shot down, in the case of military practice target drones). In popular media, the most common term used is “UAV,” which at one point stood for Unmanned Aircraft Vehicle, but also Unmanned Aerial Vehicle. The “unmanned” designation was then changed to “unoccupied,” or in some instances “uninhabited,” as plenty of “occupied” aircraft are piloted by women. Adding further confusion, some entities, primarily military and governmental (like NOAA), are now using the term UAS, which stands for Unmanned Aircraft System, the “system” designator being used to identify not only the aircraft itself, but the ground control system and whatever communications and data link components are used. Adding further to this confusing acronym stew are RPV and RPA, which, used by only a few, stand for Remotely Piloted Vehicle and Remotely Piloted Aircraft, respectively. Regardless of the acronym used, they all refer to the same concept: Operators of these craft remain safely on terra firma, and are not in the craft themselves.

A Wide Spectrum of Uses

UAVs for weather research aren't being used exclusively for hurricanes and other cyclonic storms, however. They are proving their utility in a full spectrum of atmospheric science research, particularly in remote areas and regions of meteorological extremes. Sharon Corona, of AAI, describes an Aerosonde mission in Terra Nova Bay, Antarctica. “The Aerosonde Mark 4 flew in temperatures as cold as −38°C (−36.4°F), and remained aloft up to 17 hours straight.” The mission's focus was to observe the influence of katabatic winds on the Antarctic coast to help determine what, if any, influence these winds have on global climate. She adds, “For this mission the Aerosonde aircraft were fitted with meteorological instruments to measure pressure, temperature, relative humidity, winds, net radiation, surface temperature, and ice thickness.” Some of the sensors included a laser surface profiler, surface temperature sensor, and among others, a dropsonde system, which is a device equipped with a GPS and atmospheric sensors that is dropped from an aircraft to gather and transmit atmospheric profile data during its descent. Corona concludes that while the aircraft and sensors were deployed into a high risk environment, “The operators remained safe in controlled conditions out of harm's way.” Because the system employed satellite communication, operators could control the aircraft beyond line-of-sight.

Some other meteorological applications for which UAVs have been recently used include collecting high-altitude samples of ozone, carbon dioxide, and other airborne chemicals and particulate matter; observation of forest fires; and cloud mapping, to name a few. As engineers continue to improve engine performance and efficiency, refine flight control and stabilization systems, and enhance high-resolution still and video cameras and environmental sensors—and as these components become cheaper—ever more of the heavy-lift work of airborne atmospheric research will be carried by UAVs. “It's all about filling in data gaps where we can't currently gather info,” states Lieutenant Commander Phil Eastman, NOAA Aircraft Operations Center's Unmanned Aircraft Systems officer. “This is as described [with the Aerosonde in Ophelia] at low level in storms but also in regions where we can't get an asset due to range issues such as the Bering Sea, the middle of the Pacific, the Arctic Ocean, and so on.” He then notes a limitation of aerial-based atmospheric research rooted not in safety, but in raw logistics, and explains how UAVs provide a solution: “We can't always get the right type of aircraft into certain places because there isn't anywhere to get fuel. UAS [unmanned aircraft systems] have amazing endurance numbers that can get to these places and back safely.”

Engineers are now even testing hybrid “occupied/unoccupied” systems. During one particular flight test of the Aerosonde, researchers on board a NOAA Orion controlled the Aerosonde from a base station mounted in their aircraft. Operationally, the first hybrid system will be used in 2012, when NOAA crewmembers will deploy the eight-pound, three-foot-long, electric motor-powered “Gale” UAV through a tube in the belly of an Orion into cyclonic storms. After release, Gale will unfold its composite wings and dive to approximately 100 feet above sea level, where it will fly throughout a small part of the storm and transmit wind speed, temperature, barometric pressure, and other data back to the “mother ship,” flying in comparative safety thousands of feet above. When the onboard batteries have died (after about an hour), Gale will glide into the water and end its short life. Dozens of these tiny UAVs deployed during each flight into a storm will yield yet another trove of data for scientists, as the system matures.

Will UAVs ever completely replace human-occupied aviation for weather and atmospheric research? Realistically no, at least not any time soon. In fact, experts in the field urge caution, not only in thinking in terms of UAVs replacing traditional aircraft, but even in comparing them. “I think the constant comparison to manned aircraft misses the mark. It is not a contest to see who is better. Instead, they represent additional new capabilities we can use in service of science and society,” states Eastman. He then describes a concept well known to aviators of all types, but with emphasis on weather research—situational awareness: “For missions involving ‘naked-eye’ surveying, the capabilities of the human eye remain far superior to any technology in existence today.” He notes further, “Certain missions will always require manned flight, and a widespread use of UAS is years off, but it certainly will come, sooner or later.” Eastman adds that current limitations for UAV use in atmospheric science research are rooted not in technology or even risk, but in regulation. “The current focus is either large UAS such as Global Hawk that can fly above controlled airspace, or small UAS that can fly low and within line-of-sight. Everything in the middle is too hard to use in a practical manner, due to lack of airspace access under current Federal Aviation Regulations.”

Caption: Laser Radar array used for atmospheric research, and Global Hawk.

Caption: Laser Radar array used for atmospheric research, and Global Hawk.

Caption: Dropsonde dispenser used in Global Hawk.

Caption: Dropsonde dispenser used in Global Hawk.

Caption: Gale UAV, small UAV to be dropped by NOAA Orion Hurricane Hunting Aircraft.

Caption: Gale UAV, small UAV to be dropped by NOAA Orion Hurricane Hunting Aircraft.

Caption: Global Hawk in flight, with condensation trail.

Caption: Global Hawk in flight, with condensation trail.

ED DARACK is an independent writer and photographer. Visit his website at www.darack.com.

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