Synonyms: 
DC8
DC-8
NASA DC8
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Nuclei-Mode Aerosol Size Spectrometer

The nucleation-mode aerosol size spectrometer (NMASS) measures the concentration of particles as a function of diameter from approximately 4 to 60 nm. A sample flow is continuously extracted from the free stream using a decelerating inlet and is transported to the NMASS. Within the instrument, the sample flow is carried to 5 parallel condensation nucleus counters (CNCs) as shown in Fig. 1. Each CNC is tuned to measure the cumulative concentration of particles larger than certain diameter. The minimum detectable diameters for the 5 CNCs are 4.0, 7.5, 15, 30 and 55 nm, respectively. An inversion algorithm is applied to recover a continuous size distribution in the 4 to 60 nm diameter range.

The NMASS has been proven particularly useful in measurements of nucleation-mode size distribution in environments where concentrations are relatively high and fast instrumental response is required. The instrument has made valuable measurements vicinity of cirrus clouds in the upper troposphere and lower stratosphere (WAM), in the near-field exhaust of flying aircraft (SULFUR 6), in newly created rocket plumes (ACCENT), and in the plumes of coal-fired power plants (SOS ’99). The instrument has flown on 3 different aircraft and operated effectively at altitudes from 50 m to 19 km and ambient temperatures from 35 to -80ºC.

Accuracy. The instrument is calibrated using condensationally generated particles that are singly charged and classified by differential electrical mobility. Absolute counting efficiencies are determined by comparison with an electrometer. Monte carlo simulations of the propagation of uncertainties through the numerical inversion algorithm and comparison with established laboratory techniques are used to establish accuracies for particular size distributions, and may vary for different particle size distributions. A study of uncertainties in aircraft plume measurements demonstrated a combined uncertainty (accuracy and precision) of 38%, 36% and 38% for number, surface and volume, respectively.

Precision. The precision is controlled by particle counting statistics for each channel. If better precision is desired, it is necessary only to accumulate over longer time intervals.

Response Time: Data are recorded with 10 Hz resolution, and the instrument has demonstrated response times of this speed in airborne sampling. However the effective response time depends upon the precision required to detect the change in question. Small changes may require longer times to detect. Plume measurements with high concentrations of nucleation-mode particles may be processed at 10 Hz.

Specifications: Weight is approximately 96 lbs, including an external pump. External dimensions are approximately 15”x16”x32”. Power consumption is 350 W at 28 VDC, including the pump.

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Dual-Frequency Airborne Precipitation Radar

The Second Generation Precipitation Radar (PR-2) is a dual-frequency, Doppler, dual-polarization radar system.

The airborne PR-2 system includes a real-time pulse compression processor, a fully-functional control and timing unit, and a very compact LO/IF module, all of which could be used in spaceborne applications.

The RF circuitry can be divided into two categories: circuits operating at frequencies of less than 1.5 GHz and circuits operating at frequencies above 1.5 GHz. The lower frequency (below 1.5 GHz) circuitry is all contained in a single unit, the local oscillator / intermediate frequency (LO/IF) module. This unit converts transmit chirp signals from 15 MHz up to 1405 MHz and downconverts received IF signals from 1405 MHz to 5 MHz. The unit contains both upconversion channels and all four receive channels and fits into the equivalent of a double wide 6U-VME card.

The RF front-end electronics are unique to the airborne PR-2 design and consist of five units: one local oscillator / up converter (LO/U) unit, two TWTAs and two waveguide front end (WGFE) units. In the DC-8 installation, the two TWTAs are stacked vertically in a standard rack with the LO/U in between them and the two WGFEs are mounted on top of the antenna pressure box, near the antenna feed. A calibration loop is included for each channel. This feeds some of the transmit power to the receiver, allowing in-flight variations of the transmit power and receiver gain to be monitored and removed from the data.

The digital electronics consists of a control and timing unit (CTU), an arbitrary waveform generator (AWG), and a data processor. The CTU generates the pulse timing and all other timing signals. It also provides control signals to RF. The AWG is loaded with a digital version of the linear FM chirp that is to be transmitted. The data processor is based on FPGA technology. It performs pulse compression and averaging in real-time.

The 4 MHz bandwidth received signals are sampled at 20 MHz, then digitally downconverted to complex samples, resulting in I and Q samples at 5 MHz rate. The data processor also includes pulse-pair Doppler processing. The output of the processor is the lag-0 (power) and lag-1 (complex Doppler data) for the co- and crosspolarized channels at each frequency. A VME-based workstation runs the radar, including ingesting and saving the processed data. Following calibration on the ground, the PR-2 data are stored in an HDF format.

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PeroxyAcetylNitrate, Aldehydes and Ketones

The Ames PANAK instrument is a computerized 3- channel Capillary Gas Chromatographic system designed for the collection and analysis of low ppt (10-12 v/v) levels of peroxyacyl nitrates (PANs), alkyl nitrates, and tertrachloroethene in Channels 1 and 2; and C2-C3 aldehydes, C1-C2 alcohols, C3-C4 ketones, and C1-C2 nitriles in channel 3. Channels 1 and 2 use ECD detectors and have a sampling frequency of 2.5 minutes. Channel 3 uses a Photo Ionization detector placed in series with a Reduction Gas detector and has a sampling frequency of 5 minutes. The main manifold draws 5 SL/min of ambient air through a heated Teflon lined probe from which each of the three instrument channels draws a 200 ml aliquot of sample air. This aliquot is dried by passing it through a –35 °C cold trap, cooled to -140 °C for constituent pre concentration, and then heat desorbed into the gas chromatographic columns. All calibrations are performed in-flight by using an installed dilution system and in a manner that mimics ambient air sampling. Primary standards are generally referred to a series of permeation tubes. In addition high concentration standards are also carried on board. Sensitivities under typical conditions are: 1-3 ppt PANs, 1-5 ppt alkyl nitrates, 5-20 ppt OVOC, and 20-30 ppt nitriles.

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PAN CIMS Instrument by Georgia Tech and NCAR

The PAN-CIGAR chemical ionization mass spectrometer which measures up to 7 PAN species simultaneously and semi-continuously with a time resolution of ~2 seconds. The method is based on the detection of the acylperoxy radicals formed from thermal decomposition of the PAN species at the inlet by reacting them with iodide ions, which are formed by passing methyl iodide diluted in nitrogen through an α–particle source. The reaction of the peroxy acyl radicals with I- forms IO and the acyl ion, which is detected using a quadrupole mass spectrometer (Extrel) at a mass to charge ratio of 59 in the case of PAN. The method is very specific for PAN type compounds and the limit of detection is ~1 pptv/s or better for most PAN species. The instrument employs a realtime continuous calibration using isotopically labeled PAN produced in-situ by a photolytic calibration source.

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Intensified High Definition TV Near-UV Spectrograph

NUV measures near-UV emissions of N2+ and CN molecules from air plasma and ablation products.

This instrument consists of an intensified high definition TV camera equipped with a transmission grating with 600 grooves per mm, blazed at 550 nm, made by Jobin Yvon. The camera has a blue sensitive 1-inch 2M-pixel FIT CCD, which has a resolution of 1150 TV lines. A 50 mm f1.0 lens provides a large 37 x 21 degree field of view. No coaligned camera is needed.

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JPL Mark IV Balloon Interferometer

The MkIV interferometer operates in solar absorption mode, meaning that direct sunlight is spectrally analyzed and the amount of various gases at different heights in the Earth's atmosphere is derived from the shapes and depths of their absorption lines. The optical design of the MkIV interferometer is based largely on that of the ATMOS instrument, which has flown four times on the Space Shuttle. The first three mirrors in the optical path comprise the suntracker. Two of these mirrors are servo-controlled in order to compensate for any angular motion of the observation platform. The subsequent wedged KBr plates, flats, and cube-corner retro-reflectors comprise a double-passed Michelson interferometer, whose function is to impart a wavelength-dependent modulation to the solar beam. This is achieved by sliding one of the retro-reflectors at a uniform velocity so that the recombining beams interfere with each other. A paraboloid then focusses the solar beam onto infrared detectors, which measure the interferometrically modulated solar signal. Finally, Fourier transformation of the recorded detector outputs yields the solar spectrum. An important advantage of the MkIV Interferometer is that by employing a dichroic to feed two detectors in parallel, a HgCdTe photoconductor for the low frequencies (650-1850 cm-1) and a InSb photodiode for the high frequencies (1850-5650 cm-1), the entire mid-infrared region can be observed simultaneously with good linearity and signal-to-noise ratio. In this region over 30 different gases have identifiable spectral signatures including H2O, O3, N2O, CO, CH4, NO, NO2, HNO3, HNO4, N2O5, H2O2, ClNO3, HOCl, HCl, HF, COF2, CF4, SF6, CF2ClCFCl2, CHF2Cl, CF2Cl2, CFCl3, CCl4, CH3Cl, C2H2, C2H6, OCS, HCN, N2, O2, CO2 and many isotopic variants. The last three named gases, having well known atmospheric abundances, are important in establishing the observation geometry of each spectrum, which otherwise can be a major source of uncertainty. Similarly, from analysis of T-sensitive CO2 lines, the temperature profile can be accurately determined. The simultaneity of the observations of all these gases greatly simplifies the interpretation of the results, which are used for testing computer models of atmospheric transport and chemistry, validation of satellite data, and trend determination.

Although the MkIV can measure gas column abundances at any time during the day, the highest sensitivity to atmospheric trace gases is obtained by observing sunrise or sunset from a balloon. The very long (~ 400 km) atmospheric paths traversed by incoming rays in this observation geometry also make this so-called solar occultation technique insensitive to local contamination.

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Balloon, DC-8 - AFRC
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Meteorological Measurement System

The Meteorological Measurement System (MMS) is a state-of-the-art instrument for measuring accurate, high resolution in situ airborne state parameters (pressure, temperature, turbulence index, and the 3-dimensional wind vector). These key measurements enable our understanding of atmospheric dynamics, chemistry and microphysical processes. The MMS is used to investigate atmospheric mesoscale (gravity and mountain lee waves) and microscale (turbulence) phenomena. An accurate characterization of the turbulence phenomenon is important for the understanding of dynamic processes in the atmosphere, such as the behavior of buoyant plumes within cirrus clouds, diffusions of chemical species within wake vortices generated by jet aircraft, and microphysical processes in breaking gravity waves. Accurate temperature and pressure data are needed to evaluate chemical reaction rates as well as to determine accurate mixing ratios. Accurate wind field data establish a detailed relationship with the various constituents and the measured wind also verifies numerical models used to evaluate air mass origin. Since the MMS provides quality information on atmospheric state variables, MMS data have been extensively used by many investigators to process and interpret the in situ experiments aboard the same aircraft.

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JPL Laser Hygrometer

The JPL Laser Hygrometer (JLH) is an autonomous spectrometer to measure atmospheric water vapor from airborne platforms. It is designed for high-altitude scientific flights of the NASA ER-2 aircraft to monitor upper tropospheric (UT) and lower stratospheric (LS) water vapor for climate studies, atmospheric chemistry, and satellite validation. JLH will participate in the NASA SEAC4RS field mission this year. The light source for JLH is a near-infrared distributed feedback (DFB) tunable diode laser that scans across a strong water vapor vibrational-rotational combination band absorption line in the 1.37 micrometer band. Both laser and detector are temperature‐stabilized on a thermoelectrically-cooled aluminum mount inside an evacuated metal housing. A long optical path is folded within a Herriott Cell for sensitivity to water vapor in the UT and LS. A Herriott cell is an off-axis multipass cell using two spherical mirrors [Altmann et al., 1981; Herriott et al., 1964]. The laser beam enters the Herriott cell through a hole in the mirror that is closest to the laser. The laser beam traverses many passes of the Herriott cell and then returns through the same mirror hole to impinge on a detector.

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Multichannel Coherent Radar Depth Sounder

The Center for Remote Sensing of Ice Sheets (CReSIS) has developed radars (MCoRDS) that operate over the frequency range from 140 to 230 MHz with multiple receivers developed for airborne sounding and imaging of ice sheets. MCoRDS radars have an adjustable radar bandwidth of 20 MHz to 60 MHz. Multiple receivers permit digital beamsteering for suppressing cross-track surface clutter that can mask weak ice-bed echoes and strip-map synthetic aperture radar (SAR) images of the ice-bed interface. With 200 W of peak transmit power, a loop sensitivity > 190 dB is achieved. These radars are flown on twin engine and long-range aircraft including NASA P-3 and DC-8.

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MODIS/ASTER Airborne Simulator

The MASTER is similar to the MAS, with the thermal bands modified to more closely match the NASA EOS ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite instrument, which was launched in 1998. It is intended primarily to study geologic and other Earth surface properties. Flying on both high and low altitude aircraft, the MASTER has been operational since early 1998.

Instrument Type: Multispectral Imager
Measurements: VNIR/SWIR/MWIR/LWIR Imagery

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