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The mission of the Research Aviation Facility (RAF) is to develop and operate instrumented research aircraft for the atmospheric science community at a level of sophistication and operational complexity not generally available from university-based aircraft.
RAF goals are:
High-performance Instrumented Airborne Platform for Environmental Research (HIAPER). Planning for HIAPER, the next-generation NSF/NCAR research aircraft that will serve crucial geoscience research needs over the next several decades, progressed at a rapid pace in FY 1998. Discussions among the university research community, NCAR, and NSF have outlined basic requirements for HIAPER to provide access to the tropopause and lower stratosphere over much of the globe, reach remote oceanic and polar regions, and carry a broad suite of state-of-the-art sensors and instruments to accommodate diverse scientific payloads serving current and future requirements. We find that these needs can be met by current mid-size jet aircraft that can carry scientific payloads of up to 7,000 pounds, achieve altitudes of up to 50,000 feet, and cover a range of up to 7,500 miles. HIAPER will be extensively modified to support an array of advanced instrumentation, scientific workstations, and communications technologies. An aggressive program of instrumentation development within universities and NCAR will provide a suite of next-generation instrumentation for use on HIAPER and other research aircraft. Principal milestones achieved toward HIAPER planning and acquisition during the year include the following:
| a | AC = Atmospheric Chemistry, AS = Air-Sea Interaction, BL = Boundary Layer, CP = Cloud Physics, E = Evaluation of Instrument, MS = Mesoscale Studies, R = Radiative Studies. |
| b | AMTS Test utilized an additional 3.8 hours (1 flight) in FY 1999. |
| c | WiFE Test utilized an additional 9.6 hours (3 flights) in FY 1999. |
Lake-Induced Convection Experiment (Lake-ICE). During December 1997 and January 1998, RAF staff supported the deployment of the NCAR/NSF Electra in the Lake Michigan area. The primary goals of Lake-ICE were to determine the mechanisms which control the structure and evolution of mesoscale convective circulations in boundary layers over Lake Michigan and to determine the interrelationships among these mesoscale circulations, fluxes throughout the depth of the boundary layer, and cloud precipitation development. The aircraft was equipped with the ELDORA Doppler radar, fast ozone measurement, and a variety of microphysical probes, including the new Electra version of the counterflow virtual impactor (CVI) aerosol probe. In addition, a Continuous Flow Diffusion Ice Nucleus Chamber was flown for David Rogers and Paul DeMott (Colorado State University), and a TSI Aerosol Electrometer was flown for Harry Ochs (Illinois State Water Survey) and Ken Beard (University of Illinois). Seven flights were conducted under the direction of PIs George Young (Pennsylvania State University) and David Kristovich (Illinois State Water Survey). These flights were flown in coordination with the University of Wyoming King Air. The Electra and the King Air were based at the Willow Run Airport in Ypsilanti, Michigan. Data support and planning were conducted at the University of Michigan at Ann Arbor in facilities arranged for by PI Peter Sousounis (University of Michigan).
Snowband Dynamics Project (Snowband). Coincident with the Electra deployment for Lake-ICE, RAF/RSF/SSSF staff supported the Snowband Dynamics Project to study and understand the dynamic and thermodynamic structure of heavy precipitation bands that form in the northwest quadrants of continental cyclones and in "reverse lake-effect" regions west of Lake Michigan. The Lake-ICE instrumentation was complemented with the addition of the SSSF-developed GPS Dropsonde System. Due to the mutually exclusive occurrence of cold-air outbreaks studied by Lake-ICE and the heavy precipitation cyclones studied by Snowband, the two projects were easily accommodated without interference during the December 1997 and January 1998 periods. Five research flights were conducted for Snowband under the direction of PIs Robert Rauber (University of Illinois) and Harry Ochs (Illinois State Water Survey).
Solar Corona. In February 1998 RAF deployed the C-130 to Howard Air Force Base in the Panama Canal Zone to support airborne observation of a solar eclipse over the equatorial Pacific Ocean for PIs Robert MacQueen of Rhodes College and Jeffrey Kuhn of the National Solar Observatory. The project supported a variety of objectives related to understanding the spectral characteristics of coronal emissions and use of that information to infer the motion of interplanetary dust. By making observations at aircraft altitudes, absorption of IR coronal emissions by atmospheric water vapor is minimized. The PIs supplied a highly sophisticated, custom-built solar tracking device to observe the eclipse from the aircraft. Observations were made through an open port in the upper fuselage of the C-130. The aircraft was flown unpressurized and thus was limited to a maximum altitude of 18,000 ft due to crew safety regulations. Test flights simulating the difficult task of precisely aligning the aircraft track with the track of the eclipse were flown on several days prior to the eclipse. A highly successful research flight was completed on the day of the eclipse (26 February 1998).
Airborne Coherent Lidar Advanced In-flight Measurements (ACLAIM). In March and April 1998 RAF supported airborne tests of a prototype coherent lidar system developed for in-flight detection and warning of turbulence 1-3 km ahead of an aircraft. Rodney Bogue of NASA/Dryden coordinated development of the eye-safe two-micron lidar system through Coherent Technologies, Inc. and served as flight test PI. RAF and DFS provided engineering and fabrication support to install the lidar system in the cabin of the Electra and a 45° mirror assembly on the exterior of the aircraft as needed to direct the radar beam in the forward direction. Flight tests over the Colorado Front Range encountered a range of turbulent conditions. The lidar system was judged by the PI to be highly successful in its first field test. Lidar signatures indicating turbulent conditions ahead of the aircraft correlated well with turbulence measured and felt on the aircraft moments later. This technology appears to be promising for operational turbulence detection and warning on passenger and other aircraft.
Surface Heat Budget of the Arctic (SHEBA). In May and July 1998, the C-130 was deployed to Fairbanks, Alaska to support PI Judith Curry of the University of Colorado in the study of the physical processes that determine sea-ice mass balance in the Arctic Ocean. The C-130 was instrumented with a diverse suite of instruments to measure atmospheric radiation, surface energy balance, and cloud structure. A full set of microphysical probes provided coverage of the entire particle/droplet size spectrum. Other important payload components provided and supported by the RAF included the Multichannel Cloud Radiometer (MCR) used for surface and cloud mapping, the cryogenic dewpoint hygrometer, the Multiangle Aerosol Spectrometer Probe (MASP), the Ophir radiometric thermometer, the Gerber PVM-100 (for liquid water content measurements), the UV hygrometer, and the Small Community Aerosol Inlet (SCAI). The Airborne Imaging Microwave Radiometer (AIMR) was also deployed on the aircraft and supported by RSF. This instrument was used for sea ice mapping and cloud microstructure studies. A number of co-investigators participated in the C-130 deployment for SHEBA and provided important measurement capabilities. These included Jim Hudson (University of Nevada, CCN measurements), Dave Rogers (Colorado State University, ice nuclei measurements), Francisco Valero (Scripps Institution of Oceanography, broadband and spectral radiometric measurements), Paul Lawson (SPEC, Inc., cloud particle imagery), and John Hallett (University of Nevada, cloud particle measurements)
Arctic Mesosphere Temperature Study Test (AMTS Test). In August 1998 RAF supported initial ground testing of the new iron-Boltzmann-temperature lidar system developed by Chester Gardner and colleagues at the University of Illinois. This new system offers a capability to remotely measure temperature in the middle atmosphere (80 to 100 km altitude). Gardner's team worked with RAF to install the system on the Electra aircraft in preparation for eventual deployment for Arctic and tropical missions. The AMTS Test program represented the first operation of the system in an aircraft environment, where vibration and other conditions could interfere with system operation. A successful regimen of ground testing yielded valuable guidance on the need for laser system refinements. The Illinois team pursued those refinements in August and September, preparing the system for airborne testing in October.
Wildfires Experiment Test (WiFE Test). The C-130 was used by Co-PIs Terry Clark and Larry Radke of NCAR to test an experimental instrument package for the study of wildfires in the western U.S. The experiment utilized a combination of remote sensors, aerosol probes, and in-situ chemistry analyzers on the C-130 during a six-week period in September and October 1998. Key data sets were collected by the NCAR AIMR and the NASA Extended Dynamic Range Fire Imaging Spectrometer. The latter instrument has been used for thermal imaging during numerous airborne campaigns by the U.S. Forest Service. These sensors provided high altitude images of the overall structure and progression of the fires. An Inframetrics Digital IR Imager provided calibrated thermal images of the fine-scale structure of targeted hot spots. Various flight profiles were tested to see which maneuvers could provide the best means of documenting the behavior of each fire. Flight profiles were adjusted to routinely sample the resulting smoke plume, allowing combustion efficiency to be determined from the ratio of carbon monoxide to carbon dioxide in the plume. The resulting data set will be used to help test and refine the performance of Clark’s computer simulations of wildfire behavior.
Development Activities
Multichannel Cloud Radiometer (MCR).
The MCR is a cross-track scanning spectral radiometer that covers
seven bands in the visible and near IR and mounts in a wing pod on the
C-130 aircraft. RAF carried out a major refurbishment of the
instrument in FY 1997 and FY 1998 to prepare for its deployment in SHEBA in May 1998 and INDOEX in February
1999. Channel filters and other optical components were modified to
obtain spectral radiance measurements at the visible, near-IR, and IR
wavelengths of interest to SHEBA and INDOEX investigators. The circuit
boards that provide instrument control and data output were
re-designed and packaged in a new control box. New MCR data display
and processing software was developed and implemented. The instrument
was fully characterized and calibrated by Los Alamos National
Laboratory (LANL). Deployment of
the instrument in SHEBA revealed the need for additional modifications
to eliminate microphonic noise and multiplexing board problems. This
work is currently underway and will be completed prior to deployment
in INDOEX. Krista Laursen led the MCR refurbishment team.
Evaluation and Improvement of Lyman-Alpha Hygrometer. Allen Schanot is leading an RAF effort to evaluate sources of measurement error in the Lyman-alpha instrument. The goal is to improve future performance of this instrument, which serves as a critical source of high-rate humidity measurements for turbulent flux calculations. Work to date has identified three principal problems: temperature-related drift in the calibration of the instrument, degradation of humidity measurements due to wetting of optical components during cloud penetration, and limited commercial availability of critical UV source and detector components. To mitigate the temperature drift problem, sensor electronics have been moved to inside the skin of the aircraft to reduce exposure to cold ambient temperatures. A new sampling inlet reduces sensor wetting through improved separation of cloud drops from sample air. Flight testing and evaluation of these modifications to the hygrometer will continue in FY 1999. Work is proceeding to identify a reliable supplier of source and detector units.
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