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WB-57
WB57
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Methane Near IR Tunable Diode Laser Absorption Spectrometer

The tunable diode laser (TDL) absorption instrument consists of a very high resolution scanning near-infrared diode laser spectrometer. The laser diode is a 3 mW single-mode distributed feedback (DFB) InGaAsP/InP laser that is cooled and temperature stabilized via a Peltier cooler. The laser is scanned in frequency by varying the injection current linearly. The resulting frequency scan covers the entire CH4 R(3) ro-vibrational transition in the 2ν3 overtone band at 1.653 μm.

Because the line strengths are very weak for this overtone transition, the laser beam is multipassed through a custom designed low volume astigmatic Herriott cell yielding a total optical pathlength of 245 m. The transmitted light is detected by a dc-coupled InGaAsP detector and digitized by a custom 20-bit A/D converter. This ADC is synchronized to the 16-bit software generated laser scan waveform running in continuous DMA mode. The laser scans continuously over the methane absorption at a rate of 0.25 - 0.5 KHz and coadds typically 100 scans in a 2 second integration time.

By use of the Beer-Lambert law, the methane number density is calculated from the direct absorption measurements. This calculation is performed by a non-linear least squares Voigt fitting program. The program constraints include the measured cell temperature and pressure in addition to the known absorption line strengths and pressure broadening coefficients associated with the three transitions that make up the R(3) lineshape.

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Leica RC-30 metric camera

The RC-30 is an airborne film camera system, using color infrared, natural color and black and white film, to obtain high resolution earth imagery.

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Forward Scattering Spectrometer Probe

The FSSP is of that general class of instruments called optical particle counters (OPCs) that detect single particles and size them by measuring the intensity of light that the particle scatters when passing through a light beam. A Helium Neon laser beam is focused to a diameter of 0.2 mm at the center of an inlet that faces into the oncoming airstream. This laser beam is blocked on the opposite side of the inlet with an optical stop, a "dump spot" to prevent the beam from entering the collection optics. Particles that encounter this beam scatter light in all directions and some of that scattered in the forward direction is directed by a right angle prism though a condensing lens and onto a beam splitter. The "dump spot" on the prism and aperture of the condensing lens define a collection angle from about 4º - 12º.

The beam splitter divides the scattered light into two components, each of which impinge on a photodetector. One of these detectors, however, is optically masked to receive only scattered light when the particles pass through the laser beam displaced greater than approximately 1.5 mm either side of the center of focus. Particles that fall in that region are rejected when the signal from the masked detector exceeds that from the unmasked detector. This defines the sample volume needed to calculate particle concentrations.

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Single Particle Soot Photometer (NOAA)

The SP2 is a laser-induced incandescence instrument primarily used for measuring the refractory BC  (rBC) mass content of individual accumulation-mode aerosol particles. It is able to provide this data product independently of the total particle morphology and mixing state, and thus delivers detailed information not only about BC loadings, but also size distributions, even in exceptionally clean air. The instrument can also provide the optical size of individual particles containing rBC, and identify the presence of materials associated with the BC fraction (i.e. identify the rBC’s mixing state). Since its introduction in 2003, the SP2 has been substantially improved, and now can be considered a highly competent instrument for assessing BC loadings and mixing state in situ.  NOAA deploys multiple SP2s with different designs: the first was built for the WB-57F research aircraft. Two others are rack-mounted units customized at NOAA; one of the rack mounted units can be humidified, and has been deployed with a paired dry rack-mounted SP2 as the "Humidified-Dual SP2" (HD-SP2). The rack mounted units are suitable for in-cabin operations.

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Unmanned Aerial System Laser Hygrometer

ULH measures water vapor at high accuracy in the upper troposphere and lower stratosphere to meet the following science objectives:

1. validation and scientific collaboration with NASA earth-monitoring satellite missions, principally the Aura satellite, http://aura.gsfc.nasa.gov/

2. observations of stratospheric trace gases in the upper troposphere and lower stratosphere from the mid-latitudes into the tropics,

3. sampling of polar stratospheric air and the break-up fragments of the air that move into the mid-latitudes, The ULH flights on Global Hawk will advance the state of the art technologically with remote command and control. ULH will provide real-time in-situ stratospheric water vapor measurements from Global Hawk. Additionally, ULH will make continuous measurements during long-duration flights up to 33 hours, which would be impossible with manned aircraft.

The advantages of ULH over other hygrometers are:

• Small and lightweight instrument package,
• No outgassing (achieved by mounting the open-path optical cell in the free air stream),
• Fast time response measurements in and out of clouds, without contamination,
• Accurate with a low detection limit <1 ppmv.

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Whole Air Sampler

The Whole Air Sampler (WAS) collects samples from airborne platforms for detailed analysis of a wide range of trace gases. The compounds that are typically measured from the WAS includes trace gases with sources from industrial midlatitude emissions, from biomass burning, and from the marine boundary layer, with certain compounds (e.g. organic nitrates) that have a unique source in the equatorial surface ocean. The use of a broad suite of tracers with different sources and lifetimes provides powerful diagnostic information on air mass history and chemical processing that currently is only available from measurements from whole air samples. Previous deployments of the whole air sampler have shown that the sampling and analytical procedures employed by our group are capable of accessing the wide range of mixing ratios at sufficient precision to be used for tracer studies. Thus, routine measurement of species, such as methyl iodide, at <= 0.1 x 10-12 mole fraction, or NMHC at levels of a few x 10-12 mole fraction are possible. In addition to the tracer aspects of the whole air sampler measurements, we measure a full suite of halocarbon species that provide information on the role of short-lived halocarbons in the tropical UT/LS region, on halogen budgets in the UT/LS region, and on continuing increasing temporal trends of HFCs (such as 134a), HCFCs (such as HCFC 141b), PFCs (such as C2F6), as well as declining levels of some of the major CFCs and halogenated solvents. The measurements of those species that are changing rapidly in the troposphere also give direct indications of the age and origin of air entering the stratosphere.

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Video Ice Particle Sampler

The VIPS is an electro-optical instrument used to collect and record a continuous sample of cloud particles down to 5 um. Particles are collected continuously on a looped belt coated with silicone oil. The portion of the belt exposed to the airstream is imaged by two very high resolution charged coupled device (CCD) shuttered video cameras with different resolutions. The resulting imagery is available for real-time, in-flight evaluation of cloud conditions and for post-flight habit classification and spectra analysis.

The VIPS system is composed of two parts: (1) an electro-optical collection and imaging unit mounted in a standard particle measurement system (PMS) can, and (2) data acquisition and recording components. Aperture width of the collection subassembly is adjustable for varying flight conditions. The CCD imaging cameras are coupled with inline, high detail video enhancers. Particle imagery is recorded continuously at 30 Hz on high-resolution Hi-8 VCRs. Images are also captured at 1 Hz, digitized in real-time and recorded on an Apple PowerPC.

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Tropospheric Wind Lidar Technology Experiment

The TWiLiTE instrument is a compact, rugged direct detection scanning Doppler lidar designed to measure wind profiles in clear air from 18 km to the surface. TWiLiTE operates autonomously on NASA research aircraft (ER-2, DC-8, WB-57, Global Hawk). Initial engineering flight tests on the NASA ER-2 in 2009 demonstrated autonomous operation of all major systems. TWiLiTE will be reconfigured to fly on the NASA Global Hawk as part of the Hurricane and Severe Storm Sentinel Venture Class Mission.

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SPP-100

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National Airborne Sounder Testbed - Interferometer

The National Airborne Sounder Testbed-Interferometer (NAST-I) is a high spectral resolution (0.25cm-1) and high spatial resolution (0.13 km linear resolution per km of aircraft flight altitude, at nadir) scanning (2.3 km ground cross-track swath width per km of aircraft flight altitude) interferometer sounding system that was developed to be flown on high-altitude aircraft to provide experimental observations needed to finalize the specifications and to test proposed designs and data processing algorithms for the Cross-track Infrared Sounder (CrIS) flying on the Suomi NPP (SNPP) and Joint Polar Satellite System (JPSS) platforms. Because the NAST-I infrared spectral radiance and temperature, humidity, trace species, cloud and surface property soundings have unprecedented spectral and high spatial resolution, respectively, the data can be used to support a variety of satellite sensor calibration / validation and atmospheric research programs. The NAST-I covers a spectral range from ~ 600-2900 cm-1 (3.5-16 microns) with 0.25 cm-1 spectral resolution, yielding more than 9000 spectral channels of radiance emission/absorption information. The NAST-I passive infrared (IR) Michelson interferometer is often flown with the NAST passive microwave sounding instrument (NAST-M, from MIT LL) to provide an all-weather sounding capability. The NAST-I instrument has flown numerous science missions on the ER-2, WB-57, and Proteus aircraft, and the team has evaluated efforts needed to become operational on the DC-8. Additional information can be obtained from Anna Noe (anna.m.noe@nasa.gov, 757-864-6466) or Dr. Allen Larar (Allen.M.Larar@nasa.gov, 757-864-5328).

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Anna Noe (Mgr)

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