NASA HS3 instrument views two dimensions of clouds

The second Cloud Physics Lidar built to fly on NASA's unmanned Global Hawk aircraft. In this summer's Hurricane and Severe Storm Sentinel or HS3 mission, the CPL is studying the changing profile of the atmosphere in detail to learn more about how hurricanes form and strengthen. Credit: NASA

Looking out the window of a commercial plane during takeoff is like taking the nickel tour of the profile of the atmosphere. As the plane ascends, what may start as a gloomy day on the ground, can turn into rain streaking across the window as you pass through the white-gray cloud, and then sunny skies above once the plane reaches cruising altitude.

NASA's Cloud Physics Lidar (CPL) instrument, flying aboard an unmanned Global Hawk aircraft in this summer's Hurricane and Severe Storm Sentinel, or HS3, mission, is studying the changing profile of the atmosphere in detail to learn more about how hurricanes form and strengthen.

"CPL profiles the atmosphere to get a two-dimensional picture of cloud and aerosols, from the top down," said Matt McGill of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who led the instrument team that designed and built the CPL. Its data, presented as if it were a curtain hanging from the sky, shows what's in the atmosphere's different layers.

From about 60,000 feet on the Global Hawk, twice the altitude of a commercial plane, 94 percent of the atmosphere lies below the instrument. The lidar works by sending rapid pulses of light that, like a radar beam, bounce and scatter off any particles they encounter, such as cloud droplets or dust particles. Some of the scattered light returns to the instrument where it records how long it took for the photons to leave and return -- giving the altitude of the particles.

CPL sends out 5,000 pulses of light per second in three different wavelengths, allowing the science team to discriminate between different types of particles, McGill said. "Is it a cloud made of water? Is it a cloud made of ice or mixed [water and ice]? And we can say something about what type of airborne particle we are seeing. Is it dust or smoke or pollution?"
For the scientists studying hurricanes, those distinctions are important. One of the major areas of study is how Saharan dust off of Africa travels across the Atlantic and affects hurricane formation and intensification. CPL data have been used to verify model projections of Saharan dust in the tropics. The CPL data showed dust layers had a vertical distribution different than models predicted. Instead dust layers occupied narrower altitude ranges. The finding led to an improvement in the dust models, which then feed into hurricane models.

Situated in the nose of the Global Hawk flying over the storm environment, CPL also has a role in on-the-fly mission planning. While in flight, the CPL sends its data back to the team on the ground. "The mission scientists involved in the flight planning can sit there and watch the data with us in real time and say, 'Oh, we're not getting what we want.' Then they can go work with the flight planners and pilots to reroute the aircraft into different areas," said McGill. "They love that."

The airborne science community takes full advantage of the quick look capability, as well as the 24-hour turn around for the final data products. CPL is one of the most flown instruments in NASA's Earth science fleet. "It's a workhorse for the field campaigns," said McGill.

The original CPL was built in 1999 and took its first flight on the ER-2 high altitude research aircraft in 2000. Over the years CPL has been used as a satellite simulator for ground validation efforts, a cloud spotter for other instruments needing a clear view of the ground, as well as the main data collector for scientists studying atmospheric composition and Earth's energy budget where thin clouds and aerosols are major players. The lidar was also part of the proof of concept flights for the A-Train, a series of satellites flying in the same orbit making near-simultaneous measurements of the Earth system using many different instruments. That proof of concept airborne campaign showed scientists the power of combining multiple Earth observing data sets.

In 2007, when talk began of using Global Hawks for Earth science, CPL was among the first sensors considered; its size is perfect for the instrument compartment. Worries about the untested Global Hawk led to a second nearly identical instrument being built for use on the unmanned aircraft. It flew on NASA's maiden Global Hawk Pacific campaign in 2009. Since then, the Global Hawk CPL has flown in two multi-year campaigns, alternating between the Airborne Tropical Tropopause Experiment (ATTREX) and HS3.

Compact and fully autonomous, the CPL lidar design pioneered photon-counting technology that has led to the development of two instruments that will fly in space, the Cloud-Aerosol Transport System (CATS), which launches to the International Space Station this December, and the Advanced Topographic Laser Altimeter System (ATLAS), which will fly on the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) scheduled to launch in 2017.

The solid design of the instrument has borne up surprisingly well over the years, said McGill, who uses CPL as a learning tool for interns and young scientists getting their hands dirty in the field. Together, the twin CPL instruments have flown 26 missions. HS3 will mark the 27th overall and the seventh for the Global Hawk CPL.

"It's still going strong," McGill said.

The HS3 mission is funded by NASA Headquarters and overseen by NASA's Earth System Science Pathfinder Program at NASA's Langley Research Center in Hampton, Virginia, and is one of five large field campaigns operating under the Earth Venture program. The HS3 mission also involves collaborations with partners including the National Centers for Environmental Prediction, Naval Postgraduate School, Naval Research Laboratory, NOAA's Hurricane Research Division and Earth System Research Laboratory, Northrop Grumman Space Technology, National Center for Atmospheric Research, State University of New York at Albany, University of Maryland -- Baltimore County, University of Wisconsin and University of Utah. The HS3 mission is managed by the Earth Science Project Office at NASA's Ames Research Center in Moffett Field, California. The aircraft are maintained and based at NASA's Armstrong Flight Research Center in Edwards, California.

Source: NASA

Subtle shifts in the Earth could forecast earthquakes, tsunamis

University of South Florida graduate student Denis Voytenko prepares a GPS unit for a high-precision geodetic measurement.
Credit: Jacob Richardson

Earthquakes and tsunamis can be giant disasters no one sees coming, but now an international team of scientists led by a University of South Florida professor has found that subtle shifts in Earth's offshore plates can be a harbinger of the size of the disaster.

In a new paper published in the Proceedings of the National Academy of Sciences, USF geologist Tim Dixon and the team report that a geological phenomenon called "slow slip events" identified just 15 years ago is a useful tool in identifying the precursors to major earthquakes and the resulting tsunamis. The scientists used high precision GPS to measure the slight shifts on a fault line in Costa Rica, and say better monitoring of these small events can lead to better understanding of maximum earthquake size and tsunami risk.

"Giant earthquakes and tsunamis in the last decade -- Sumatra in 2004 and Japan in 2011 -- are a reminder that our ability to forecast these destructive events is painfully weak," Dixon said.

Dixon was involved in the development of high precision GPS for geophysical applications, and has been making GPS measurements in Costa Rica since 1988, in collaboration with scientists at Observatorio Vulcanológico y Sismológico de Costa Rica, the University of California-Santa Cruz, and Georgia Tech. The project is funded by the National Science Foundation.

Slow slip events have some similarities to earthquakes (caused by motion on faults) but release their energy slowly, over weeks or months, and cannot be felt or even recorded by conventional seismographs, Dixon said. Their discovery in 2001 by Canadian scientist Herb Dragert at the Pacific Geoscience Center had to await the development of high precision GPS, which is capable of measuring subtle movements of the Earth.

The scientists studied the Sept. 5, 2012 earthquake on the Costa Rica subduction plate boundary, as well as motions of the Earth in the previous decade. High precision GPS recorded numerous slow slip events in the decade leading up to the 2012 earthquake. The scientists made their measurements from a peninsula overlying the shallow portion of a megathrust fault in northwest Costa Rica.

The 7.6-magnitude quake was one of the strongest earthquakes ever to hit the Central American nation and unleased more than 1,600 aftershocks. Marino Protti, one of the authors of the paper and a resident of Costa Rica, has spent more than two decades warning local populations of the likelihood of a major earthquake in their area and recommending enhanced building codes.

A tsunami warning was issued after the quake, but only a small tsunami occurred. The group's finding shed some light on why: slow slip events in the offshore region in the decade leading up to the earthquake may have released much of the stress and strain that would normally occur on the offshore fault.

While the group's findings suggest that slow slip events have limited value in knowing exactly when an earthquake and tsunami will strike, they suggest that these events provide critical hazard assessment information by delineating rupture area and the magnitude and tsunami potential of future earthquakes.

The scientists recommend monitoring slow slip events in order to provide accurate forecasts of earthquake magnitude and tsunami potential.

Source: University of South Florida (USF Health)