The Global Hawk Unmanned Aircraft Systems overcome several limitations that once kept researchers from studying how hurricanes evolve and why. Not only can they fly to an altitude of about 60,000 feet-about twice as high as a commercial airliner-and as far as 12,600 miles, they also can fly for about 26 hours, according to NASA. This gives researchers the time, distance and altitude they need to collect continuous, high-resolution measurements that will help better predict storm intensity.
“They have very long endurance,” Heymsfield says. “They can fly for about 26 hours or so, and for studying a hurricane far out in the Atlantic Ocean, we need at least this much endurance for the plane to fly over the storm far from the coast. Any plane with a pilot is limited to 8 hours or so of flight time. This allows us to study storms way out over the ocean.”
Altitude is important too, Heymsfield says, because it enables researchers to get a better look inside the storms with the state-of-the art science instruments the Global Hawks use to study tropical storms and hurricanes. “We measure the structure of storms any where there is precipitation and clouds that the radar can detect,” Heymsfield says. “We measure the wind velocity and wind speeds within a storm. By looking at these winds it helps us understand how a storm intensifies.”
During this mission, according to NASA, scientists want to use data from the Global Hawk flights to answer three main questions-what role does the large-scale environment, particularly the Saharan Air Layer (SAL), have on intensity change, what is the role of storm internal processes such as convective towers, and to what extent are these intensification processes predictable. The two Global Hawks that are part of the HS3 mission are equipped with different payloads. The environmental payload is responsible for monitoring the environment around the storms looking for conditions that are “favorable for storm formation and intensification,” according to NASA. The state-of-the art weather instruments that make this possible are the scanning High-resolution Interferometer Sounder (S-HIS), the AVAPS dropsonde system, theTWiLiTE Doppler wind lidar, and the Cloud Physics Lidar (CPL). This Global Hawk is involved with studying the role SAL has on storm formation and intensification.
The over-storm payload, which features NovAtel's SPAN technology, repeatedly flies directly over storms to “collect data on the inner-core structures that lead to storm intensity change,” according to NASA. This Global Hawk is not only equipped with the SPAN system, it also collects field measurements using HIWRAP conically scanning Doppler radar. The radar works in conjunction with the SPAN technology, the HIRAD multi-frequency interferometric radiometer, and the HAMSR microwave sounder.
While the Global Hawks provide hurricane data that researchers wouldn't otherwise be able to obtain, that data must be accurate. That's where NovAtel's SPAN technology comes in.
NovAtel is the leading provider of high-precision GNSS technology for unmanned systems making it a natural fit for the HS3 mission. NovAtel technology has been used in Unmanned Aircraft Systems, Unmanned Airborn Vehicles and Unmanned Ground Vehicles, and in a range of applications from homeland security to aerial survey to mine detection.
The over-storm payload Global Hawk is equipped with a NovAtel SPAN-SE receiver which provides the user interface to SPAN and outputs raw measurement data or solution data over several communication protocols or to a removable SD card.
As the principal investigator on the HIRWAP radar, Heymsfield works closely with the SPAN-SE technology. His primary role is to work with the radar measurements and retrievals, which is deriving the winds from the radar measurements in the storm.
“We're not doing anything in real time. We're doing post-processing,” Heymsfield said. “What we do is use the post-processed data to improve the accuracy of winds obtained from HIWRAP. We have to know the attitude of the airplane so we can remove any winds that are caused by the aircraft itself. We want to look at the winds in the storm, so we have to remove any effects of the aircraft. That means we need an accurate position and attitude of the plane.”
Heymsfield and his team use the SPAN-SE with an LN-200 IMU to provide high-accuracy attitude and position data. They can get this information from the aircraft, Heymsfield says, but the SPAN technology provides it at a higher data rate-of up to 200 Hz.
The SPAN receiver is located on top of the Global Hawk's HIWRAP radar, so it is more accurate than the aircraft system that is located about 20 feet forward of the radar location, Heymsfield says.
“It [SPAN] allows us to have high quality navigation data along with our radar data,” Heymsfield says. “It makes it easier to correct for the aircraft motions, and it makes data more accurate.”
Also in 2014, NASA used NovAtel technology in an experiment that isn't related to hurricanes. IPHEx, or the Integrated Precipitation and Hydrology Experiment,” seeks to characterize warm season orographic precipitation regimes, and the relationship between precipitation regimes and hydrologic processes in regions of complex terrain,” according to data provided by the IPHEx experiment, Civil and Environmental Engineering, Duke University, North Carolina.
The experiment included an Intense Observing Period (IOP) from May-July of 2014 post GPM launch, which is the Global Precipitation Mission, according to the website. GPM is an international satellite mission to “provide next-generation observations of rain and snow worldwide every three hours.” The observing period focused on 4D mapping of the precipitation structure. The NASA ER-2 and the UND Citation aircraft conducted high altitude and “in the column” measurements.
The ER-2 plane is equipped with multifrequency-radiometers (AMPR and CoSMIR), the dual-frequency Ka-Ku band, HIWRAP Ka-Ku band, CRS W-band, and EXRAD X-band radars. A NovAtel SPAN-SE and a ProPak-V3, both, triple-frequency GNSS receivers that track GPS+GLONASS were used.