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WB-57
WB57
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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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Harvard Lyman-α Photofragment Fluorescence Hygrometer

The Harvard Water Vapor (HWV) instrument combines two independent measurement methods for the simultaneous in situ detection of ambient water vapor mixing ratios in a single duct. This dual axis instrument combines the heritage of the Harvard Lyman-α photo-fragment fluorescence instrument (LyA) with the newly designed tunable diode laser direct absorption instrument (HHH). The Lyman-α detection axis functions as a benchmark measurement, and provides a requisite link to the long measurement history of Harvard Lyman-α aboard NASA’s WB-57 and ER-2 aircraft [Weinstock et al., 1994; Hintsa et al., 1999; Weinstock et al., 2009]. The inclusion of HHH provides a second high precision measurement that is more robust than LyA to changes in its measurement sensitivity [Smith et al., in preparation]. The simultaneous utilization of radically different measurement techniques facilitates the identification, diagnosis, and constraint of systematic errors both in the laboratory and in flight. As such, it constitutes a significant step toward resolving the controversy surrounding water vapor measurements in the upper troposphere and lower stratosphere.

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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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Multiple-Angle Aerosol Spectrometer Probe

The Multiple-Angle Aerosol Spectrometer Probe (MASP) determines the size and concentration of particles from about 0.3 to 20 microns in diameter and the index of refraction for selected sizes. Size is determined by measuring the light intensity scattered by individual particles as they transit a laser beam of 0.780µm wavelength. Light scattered from particles into a cone from 30 to 60 degrees forward and 120 to 150 degrees backwards is reflected by a mangin mirror through a condensing lens to the detectors. A comparison of the signals from the open aperture detector and the masked aperture detector is used to accept only those particles passing through the center of the laser beam. The size of the particle is determined from the total scattered light. The index of refraction of particles can be estimated from the ratio of the forward to back scatter signals. A calibration diode laser is pulsed periodically during flight to ensure proper operation of the electronics. The shrouded inlet minimizes angle of attack effects and maintains isokinetic flow through the sensing volume so that volatilization of particles is eliminated.

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Multi-sample Aerosol Collection System

The Multiple Aerosol Collection System contains an impactor collector which permits the collection of particles on electron microscope grids for later chemical-constituent analysis. The collector consists of a two stages. In the first stage the pressure of the sample is reduced by a factor of two without loosing particles by impaction on walls. The second stage consists of a thin plate impactor which collects efficiently even at small Reynolds numbers. The system collects particles as small as 0.02 micron at WB-57 cruise altitudes. As many as 24 samples can be collected in a flight.

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Isotope Ratio Infrared Spectrometer

IRIS is an ultra sensive laser spectrometer for in situ detection of the isotopic composition of water vapor in the higher tropopause and the lower stratosphere. The isotope signals may be used to quantify troposphere-stratosphere exchange, and to study the water chemistry in the stratosphere. IRIS is based on the technique of optical-feedback cavity enhanced absorption spectroscopy. It uses a room temperature infrared laser, needing no crygens. The instrument combines a low weight (< 50 kg) and volume (< 50 L) with a low power consumption (< 200 W), making it uniquely suitable for future deployment on an Unmanned Aerial Vehicle.

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Harvard Integrated Cavity Output Spectroscopy

The Harvard CRDS/ICOS instrument is an absorption spectrometer that uses the relatively new and highly sensitive techniques of integrated cavity output spectroscopy (ICOS) and cavity ringdown spectroscopy (CRDS) with a high-finesse optical cavity and a cw quantum cascade laser (QCL) source. The primary spectroscopic technique employed is ICOS, in which intra-cavity absorption is measured from the steady-state output of the cavity. Light from a high power, tunable, single mode, solid-state laser source is coupled into a cavity consisting of two concave, highly reflective mirrors (R ≈ 0.9999), through which air continuously flows. The laser is scanned over a spectral region of 1–2 cm-1 containing an absorption feature, and the cavity output is detected by an LN2-cooled HgCdTe detector. The resultant output approximates an absorption spectrum with an effective pathlength of > 5 km, far greater than that of standard multipass Herriott or White cells.

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Harvard Total Water

The design of the newly developed total water instrument is based on the same principles as the water vapor instrument, and is intended to fly in conjunction with it. Conceptually, the total water instrument can be thought of as containing four subsystems:
1. An inlet through which liquid and/or solid water particles can be brought into an instrument duct without perturbing the ambient particle density.
2. A heater that efficiently evaporates the liquid/solid water before it reaches the detection axis.
3. Ducting through which the air flows to the detection axis without perturbing the (total) water vapor mixing ratio.
4. A water vapor detection axis that accurately and precisely measures the total water content of the ambient air.

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Harvard Hydroxyl Experiment

OH is detected by direct laser induced fluorescence in the (0-1) band of the 2?-2? electronic transition. A pulsed dye-laser system produces frequency tunable laser light at 282 nm. An on-board frequency reference cell is used by a computer to lock the laser to the appropriate wavelength. Measurement of the signal is then made by tuning the laser on and off resonance with the OH transition.

Stratospheric air is channeled into the instrument using a double-ducted system that both maintains laminar flow through the detection region and slows the flow from free stream velocity (200 m/s) to 40 m/s. The laser light is beam-split and directed to two detection axes where it passes through the stratospheric air in multipass White cells.

Fluorescence from OH (centered at 309 nm) is detected orthogonal to both the flow and the laser propagation using a filtered PMT assembly. Optical stability is checked periodically by exchanging the 309 nm interference filter with a filter centered at 302 nm, where Raman scattering of N2 is observed.

HO2 is measured as OH after chemical titration with nitric oxide: HO2 + NO → OH + NO2. Variation of added NO density and flow velocity as well as the use of two detection axes aid in diagnosis of the kinetics of this titration. Measurements of ozone (by uv absorption) and water vapor (by photofragment fluorescence) are made as diagnostics of potential photochemical interference from the mechanism: O3 + hv (282 nm) → O(1D) + O2, followed by: O(1D) + H2O → OH + OH

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Diode Laser Hygrometer

The DLH has been successfully flown during many previous field campaigns on several aircraft, most recently ACTIVATE (Falcon); FIREX-AQ, ATom, KORUS-AQ, and SEAC4RS (DC-8); POSIDON (WB-57); CARAFE (Sherpa); CAMP2Ex and DISCOVER-AQ (P-3); and ATTREX (Global Hawk). This sensor measures water vapor (H2O(v)) via absorption by one of three strong, isolated spectral lines near 1.4 μm and is comprised of a compact laser transceiver and a sheet of high grade retroflecting road sign material to form the optical path. Optical sampling geometry is aircraft-dependent, as each DLH instrument is custom-built to conform to aircraft geometric constraints. Using differential absorption detection techniques, H2O(v) is sensed along the external path negating any potential wall or inlet effects inherent in extractive sampling techniques. A laser power normalization scheme enables the sensor to accurately measure water vapor even when flying through clouds. An algorithm calculates H2O(v) concentration based on the differential absorption signal magnitude, ambient pressure, and temperature, and spectroscopic parameters found in the literature and/or measured in the laboratory. Preliminary water vapor mixing ratio and derived relative humidities are provided in real-time to investigators.

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