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ATD's sea change brings a new wave of instruments

NCAR's Atmospheric Technology Division is going through what its new director, David Carlson, calls a sea change: a fundamental shift from individual systems and platforms to interactive, multiple-sensor systems that allow researchers to reach more of the atmosphere, with more kinds of sensors, to obtain more integrated results. The change is manifesting itself in a wave of improved and new systems, some in the works for some time, some the result of recent inspiration.

ATD provides the UCAR community with atmospheric observing systems and support, from research aircraft to ground-based sensors to software for data collection, display, and analysis. Over the past few years, says Carlson, the division's individual systems have blossomed into integrated systems. The Electra, once the only large plane in the NCAR/NSF fleet, is now one of three. "With the WB-57 jet and the C-130, which has terrific range and terrific payload and endurance, we're probing parts of the atmosphere we've never been before. It's like a little neighborhood has expanded to operate anywhere in the world."

Some of the most dramatic developments have been in radar.

Radar in the air

The Electra Doppler Radar (ELDORA) has taken ground-based, dual-Doppler radar ideas and put them into the air. The basic proof of concept for ELDORA was in TOGA COARE, the massive international study of the climatically critical western Pacific warm pool (see the Winter 1994 UCAR Quarterly). But Carlson says the real test of its design goals will be this spring in Oklahoma, as part of VORTEX, the Verification of the Origins of Rotation in Tornadoes Experiment. "This is the first experiment that will try ELDORA's full capabilities. We hope to test the boundaries of what was done with airborne radar."

Radar recycling

Next there's BINET (Bistatic Doppler radar receiver network), which helps a single Doppler radar act like a network. A Doppler radar measures only the component of wind blowing directly toward or away from itself. Two-dimensional wind fields can be derived from one radar, but the accuracy is limited, and two Doppler radars probing the same air space would be effective, but costly. Joshua Wurman, a former NCAR postdoctoral researcher now at the University of Oklahoma, saw an unexploited resource in the weak and scattered stray signals that the transmitting radar misses. BINET, which Wurman developed with ATD staff, uses passive receivers with wide-angle antennas to capture and use these "waste" signals. BINET can include two or more receivers at relatively low cost, and early tests show the derived wind vectors are accurate to within two meters per second. For licensing information on BINET, please contact the UCAR Foundation (see below).

Radar in big boxes

Another major development is a large modular radar to replace the CP-2. The large, domed CP-2 has been a cornerstone of ATD's surface radar offerings for years. But it is expensive to operate and difficult to move because it needs to be set up on a concrete pad. In practice, says Carlson, the only places it can be used are at the Marshall (Colorado) field site and Cape Canaveral, where the concrete pads already exist. With parts from other radars, ATD scientists and engineers have assembled S-POL (S-band polarized radar), a modular and transportable 10-centimeter-wavelength Doppler radar. It has improved capabilities (such as a high-quality antenna with higher gain and better ground clutter suppression, and a highly reliable transmitter), but the best part is how it's put together--and comes apart. The radar is built in components that fold up and fit in six van-size shipping containers called seatainers. The only site preparation needed is level ground. Four of the seatainers become a stable base, and the radar sits at the center. Shipping seatainers, Carlson adds, is easy and inexpensive. "It's an ingenious solution to a big radar problem." CP-2 will make one more trip to Florida this summer for a study of cumulus clouds. After that, its future is uncertain. It may be used for parts for S-POL, or stored and reactivated only for special projects.

Computer visualization of how S-POL would appear when complete and deployed on site. (Actual diameter of the antenna is 8.6 meters.) The radar and its instrumentation would be shipped to remote sites in six seatainers. Four of them become a base for the radar; the other two serve as an operations center. (Visualization by Steven Deyo and Jack Fox.)

Radar in a little box

One thing that limits what can be done with radar is the enormous amount of hardware needed to process the signal. In the early days, it took entire trailers to handle it all, and hardware still imposes a serious limitation, especially on aircraft. "Planes have standard weather-avoidance radars, but to record the data from them or put them to another use would require a whole rack of filters and converters," says Carlson. "It's the same with BINET. It's fairly simple radar processing, but it needs compact, efficient processing units." The ATD solution: PIRAQ (PC Integrated Radar Acquisition) or "radar in a PC." In PIRAQ, hardware needed for signal processing has been reduced to a single PC card. "Suddenly," says Carlson, "all the size, weight, and complexity have gone way down." PIRAQ can digitize and make coherent Doppler radar signals out of the nose radar in planes. It makes a BINET array of ten receivers feasible and cheap. It allows scientists to retrieve vertical velocity (as often as every 10 seconds) from ISS profilers (see below). The user can configure the software to suit his or her needs.

Mitchell Randall holds PIRAQ, the compact card he and Eric Lowe developed to turn a personal computer into a radar receiver. (Photo by Carlye Calvin.)

Surface systems

The Integrated Sounding System (ISS), first used in TOGA COARE, "has turned out to be a rich facility for research," says Carlson. The basic system consisted of four subsystems: a balloon-borne radiosonde navigation system, a surface observing station (two instrumented towers collecting standard meteorological readings and a rain gauge), a Doppler wind-profiling radar, and a Radio Acoustic Sounding System. The unique feature of ISS is not the components, but their integration in a single portable system with full ATD field support. To the "basic ISS" other researchers add their own instruments. Recently, ATD entered into a cooperative agreement with NOAA's Environmental Technology Laboratory to add an upward-looking ground-based lidar to measure atmospheric aerosols.

The eagerly awaited PAM (portable automated mesonet) III, the new generation of ATD's all-purpose meteorological station, includes new sensors, lower maintenance, faster data transmission, and more accurate measurements. It can now make measurements fast enough to get surface fluxes--heat, moisture, momentum--as well as point measurements, says Carlson. ATD plans to have three of the stations ready for field use by midsummer and ultimately as many as 30 may be built, depending on user demand. Carlson sees PAM III as a powerful complement for the Atmosphere/Surface Turbulent Exchange Research (ASTER) facility, which measures many of the same parameters as PAM, plus chemical fluxes. ASTER will continue to be the central facility for investigating surface exchange processes, but PAM is more portable and several of them could serve as remote flux stations to give a broader geographic perspective to ASTER's measurements. PAM III, Carlson concludes, provides a smaller, slightly different capability that can be put in remote locations. With its ability to transmit data via satellite, it can operate untended anywhere from Mongolian grasslands to Saharan sands.

GPS dropwindsonde

For years, the Omega satellite navigation system has been the mainstay for guiding planes and ships or tracking radiosondes. But this system is scheduled to end in a few years and the Global Positioning System has been replacing a lot of what people do with Omega. Says Carlson: "We're rebuilding our dropwindsondes to work with GPS rather than Omega. It's something we'll have to do anyway, but it also gives us the chance to explore what this technology can do for us." What it can do is so impressive it can be confusing. In initial tests, ATD engineers thought the data from the descending sonde looked unduly noisy. On closer examination it turned out that what was being registered was the swinging of the instrument as it dangled from its parachute.

These are just some of the newest and brightest examples of what ATD offers. They are clear indications of the new directions the division is taking to provide what the community needs. As Carlson puts it, "sometimes we may be ahead of the field, sometimes a little behind, but I think what we're doing reflects the way the science is going. Global projects need integrated measurements."

For further information on ATD and its facilities, see the ATD home page:

For specific information on BINET, ELDORA, S-POL, or PIRAQ, please contact Peter Hildebrand (peter@ucar.edu; 303-497-2050).

For information on ISS, contact Walter Dabberdt (dabberdt@ucar.edu; 303-497-8819) or David Parsons (parsons@ucar.edu; 303-497-8749); on PAM III, Dabberdt or Thomas Horst (horst@ucar.edu; 303-497-8838); on the GPS dropwindsonde, Dabberdt or Harold Cole (cole@ucar.edu; 303-497-8753).

For information on licensing of BINET, please contact Wayne Moore, Technology Commercialization Program, UCAR Foundation, Box 3000, Boulder, CO 80307-3000 (wmoore@ucar.edu; 303-497-8563).

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Edited by Carol Rasmussen, carolr@ucar.edu
Prepared for the Web by Jacque Marshall
Last revised: Mon Apr 3 17:49:41 MDT 2000