Here comes HIAPER

The versatile new research aircraft gears up for its 2005 debut

by Bob Henson

After a six-year gestation period, the newest NSF/NCAR community aircraft is almost ready for delivery. HIAPER—the High-performance Instrumented Airborne Platform for Environmental Research—is due to arrive at Colorado’s Jefferson County Airport (Jeffco) in February 2005.

Backed by NSF funding to the tune of $80 million, HIAPER is the largest community project in NCAR history. The aircraft’s delivery marks the successful transformation of a corporate jet into a research vessel suited for probing the troposphere and parts of the lower stratosphere on flights that can range up to 7,000 miles (11,200 kilometers).

HIAPER

A Savannah Air Center (SAC) staff member gives the thumbs-up as HIAPER is taxied onto the SAC ramp. (Photo courtesy Michael Gemelli, Passport to Knowledge.)

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“We’ve had our share of delays, but we’ve avoided any major headaches,” says Krista Laursen, head of the HIAPER Project Office. To keep things rolling smoothly, Laursen logged hundreds of hours in e-mails, phone calls, and visits with the Gulfstream employees in Savannah, Georgia, who built the aircraft, and with Lockheed Martin staff members in Greenville, South Carolina, who carried out modifications. The last pre-delivery touches are being completed by the Savannah Air Center under the supervision of Garrett Aviation Consulting Group.

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Krista Laursen. (Photo by Carlye Calvin.)

Laursen credits the close teamwork among all of the team members for keeping the project generally on time and within budget. “I think we’ve been very fortunate. Because we’ve had a regular chain of communications with Gulfstream, we’ve been able to catch problems very early and resolve them very quickly, ” she says.

After HIAPER arrives at Jeffco, the baton gets handed to dozens of NCAR engineers and technicians. They’ll be working with subcontractors to get the aircraft’s intercom, satellite communications, and other systems in place. Next summer, Gulfstream pilots will accompany their NCAR peers on test flights. A series of progressive science missions later in 2005 will test HIAPER’s mettle, relying mostly on a standard set of airborne instruments aboard flights out of Jeffco.

Regular science missions begin in 2006, and HIAPER will eventually log on the order of 400 flight hours per year. As with other NSF/NCAR aircraft, missions will be chosen by the NSF Observing Facilities Advisory Panel (OFAP) based on proposals from the research community. The first call for proposals should occur in mid-2005, says Laursen.

A whole-Earth aircraft

While it’s expected to be an instant hit among atmospheric researchers, HIAPER’s mandate goes further. “This platform is really intended to benefit the entire geoscience community, ” says Laursen. For instance, “there’s a lot of interest in remote sensing—not just atmospheric, but also terrestrial, using the aircraft to do land and ocean surveys.”

One key niche for HIAPER is the tropopause, referred to more broadly as the upper troposphere/lower stratosphere (UTLS). This part of the atmosphere is the staging ground for important vertical exchanges of momentum and air chemistry.

HIAPER’s ability to reach 51,000 feet (16,000 meters) means that it can sample the frigid tropopause everywhere but above the tropics, where the tropopause is at its highest. Coupled with its long- distance capability, HIAPER should be a popular tool for investigating ozone loss and other processes far above the Arctic and Antarctic.

Satellite calibration is another area where HIAPER should shine, given the plane’s versatile range. “We’ve been trying to estimate parameters that are difficult to extract from satellite measurements,” says Jennifer Francis (Rutgers University), a long-time member of HIAPER’s advisory committee. “How high is the cloud base, not just the cloud top? What’s the temperature distribution inside the cloud? How much humidity is there below the cloud? I can certainly see HIAPER validating what we can measure from satellites.”

Tools for the observing trade

Instrument developers at NCAR and across the country are building new tools specifically for HIAPER over the next two to four years. NSF recently awarded just under $12 million to more than a dozen principal investigators, among them Michael “MJ” Mahoney of the Jet Propulsion Laboratory (California Institute of Technology). For years NASA has relied on Mahoney’s Microwave Temperature Profiler for precise measurements aboard its high-altitude research aircraft. Now Mahoney is adapting the unique instrument design for HIAPER.

“Knowing the temperature profile is important for airborne research, especially when you’re flying near the tropopause,” says Mahoney. “You want to know whether the air you’re sampling is tropospheric or stratospheric.” Mahoney’s grant includes funds for extensive training of NCAR staff on how to operate the profiler—which is especially important, since Mahoney plans to retire in a few years. “I really want to see everything that I’ve learned over the years get transferred and be in good hands.”

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Across from the familiar NCAR hangar at Jeffco is a brand-new, twice-as-large hangar (interior, above; exterior, below), completed earlier this year. It can house both HIAPER and, when needed, either the Naval Research Laboratory P-3 (which hosts the Electra Doppler Radar) or the NSF/NCAR C-130. “We won’t have to have an aircraft sitting out on the ramp,” notes Krista Laursen, “as was the case with the Electra and the C-130 for a number of years.” (Photos by Carlye Calvin.)

HIAPER Project Office

HIAPER instrumentation PIs

Getting on the wavelength(s) of water vapor

One of the new instruments being built for HIAPER will set a new pace for water vapor cloudsmeasurement. Mark Zondlo (Southwest Sciences) is leading the development of a laser-based sensor that can accurately gauge water vapor throughout HIAPER’s entire vertical range. That’s no small measurement feat, since water vapor can occupy as little as one part per million in the tropopause but 3 or 4 parts per hundred near the surface of the tropics.

Previous laser-based hygrometers are fast and sensitive tools for sampling water vapor at high altitudes, Zondlo explains, but their narrow tuning range scans only one absorption band, which saturates at water vapor levels typical of the mid-troposphere. A slower, chilled-mirror hygrometer is often needed for humid conditions closer to the ground. “Neither instrument is great for the entire troposphere,” says Zondlo.

To address this dilemma, Zondlo is employing a new vertical cavity surface emitting laser. Its signal is broad enough to capture two absorption bands that lie close to each other. One, at a wavelength of 1854.03 nanometers, is sensitive enough to detect tiny amounts of upper-level moisture; the other, at 1853.37 nm, is robust enough to sample even the most humid regimes. Both wavelengths are scanned 25 times a second, and an algorithm switches between the two as needed.

The resulting instrument may help solve some nagging questions about water vapor in the UTLS region. In some cases, relative humidities well above 100%—even above 200%—fail to generate clouds. “We need to get a better understanding of how much water vapor is in the UTLS to understand how clouds form at these levels,” Zondlo says.

To calibrate the new instrument, Zondlo is working with Harvard University’s Elliott Weinstock and James Anderson, experts in stratospheric water vapor measurement. “It’s a nice collaboration between academia, government, and private industry,” says Zondlo.