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Water Vapor
Water

G2301-m

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G2301-f

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COMA

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NOAA Water

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Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research

4STAR has made several test flights on the PNNL G1, and its full capabilities are still being developed. When it achieves those full capabilities, we expect that, in addition to AATS-like direct-beam measurements of aerosol optical depth (AOD) and water vapor, 4STAR’s sky-scanning capabilities will permit the first airborne AERONET-like retrievals of such aerosol properties as SSA, complex refractive index, shape, and multimodal size distribution. Its zenith-viewing mode will permit retrievals of cloud optical thickness and cloud particle effective radius (when combined with a measurement of upwelling flux at two solar wavelengths), and its spectrometric resolution will permit improved aerosol-gas separation (hence improved aerosol retrievals) and possibly retrievals of additional gases. For SEAC4RS, 4STAR is offered as an option to replace AATS-14 on the DC-8 after initial science flights by AATS-14 during the Southeast Asia deployment. 4STAR has the sun-tracking capabilities of AATS and adds sky-scanning and zenith-viewing capabilities, all with spectrometers replacing the individual photodiodes of AATS-14.
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Vertical Cavity Surface Emitting Laser Hygrometer

The VCSEL hygrometer is an open-path, laser-based hygrometer that measures absolute concentration of water vapor (molecules per cm-3) at a rate of 25 Hz. The instrument is designed for operation throughout the troposphere and lower stratosphere. Two water vapor absorption lines are used: a “weak” line at 1853.37 nm for lower tropospheric mixing ratios and a “strong” line at 1854.03 nm for middle and upper tropospheric concentrations. VCSELs have a wide current tuning capability and can probe each line by changing the laser injection current with only slight adjustments to the laser temperature. Switching between the absorption lines generally occurs near a fractional absorption of 10-3, though a hysteresis is built in to prevent rapid switching near this transition (generally a factor of four in each direction). The thresholds for line switching changes slightly with temperature and pressure, but it generally is in the -15 to -25 C frost point range.

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Gulfstream V - NSF
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Harvard Harriot Hygrometer

The Harvard Herriott Hygrometer (HHH) is a multipass Herriott cell that measures water vapor via direct detection. Predicted accuracy and precision are ± 3–5% and ± 0.05 ppmv H2O, in the lower stratosphere, for a 10-s integration time, respectively. The theory and application of HHH as a water vapor instrument are laid out in the context of making accurate measurements traceable to laboratory standards. In conjunction with the Harvard Water Vapor (HWV) instrument, HHH will establish ultimate credibility via three, independent detection methods in-flight and five for laboratory and in-field calibration. A multi-detection, calibration system of this nature is beyond the scope of any in existence today. Because HHH promises such high reliability and slight margins of error, the data acquired by this instrument should minimize the uncertainty associated with natural and anthropogenic climate forcing. HHH may serve as a prototype instrument for the use of miniaturized, TDL systems as in situ quantifiers of atmospheric gases via the straightforward method of direct detection, thus extending the scientific payback of this new system.

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UAS Chromatograph for Atmospheric Trace Species

The Unmanned Aircraft Systems (UAS) Chromatograph for Atmospheric Trace Species (UCATS) was designed and built for autonomous operation on pilotless aircraft. It uses chromatography to separate atmospheric trace gases along a narrow heated column, followed by precise and accurate detection with electron capture detectors. There are two chromatographs on UCATS, one of which measures nitrous oxide and sulfur hexafluoride, the other of which measures methane, hydrogen, and carbon monoxide. In addition, there is a small ozone instrument and a tunable diode laser instrument for water vapor. Gas is pumped into the instruments from an inlet below the GV, measured, and vented. UCATS has flown on the Altair UAS, the GV during HIPPO I and II, and most recently on the NASA/NOAA Global Hawk UAS during the Global Hawk Pacific (GloPac) mission, where a record was set for the longest duration research flight (more than 28 hours). UCATS is relatively lightweight and compact, making it ideal for smaller platforms, but it is easily adaptable to a mid-size platform like the GV for HIPPO. The data are used to measure sources and sinks of trace gases involved in climate and air quality, as well as transport through the atmosphere.

UCATS is three different instruments in one enclosure:

1. 2-channel gas chromatograph (GC)
2. Dual-beam ozone photometer (OZ)
3. Tunable diode laser (TDL) spectrometer for water vapor (WV)

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N2O, SF6, CH4, CO, O3, H2, H2O
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Altair, Global Hawk - AFRC, DC-8 - AFRC, Gulfstream V - NSF, WB-57 - JSC
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Lidar Atmosphere Sensing Experiment

The Differential Absorption Lidar uses the backscatter of two simultaneous laser wavelengths through zenith and nadir windows to measure the vertical profiles of H2O and aerosols/clouds.

NASA's Lidar Atmospheric Sensing Experiment (LASE) system is an airborne DIAL (Differential Absorption Lidar) system used to measure water vapor, aerosols, and clouds throughout the troposphere. LASE probes the atmosphere using lasers to transmit light in the 815-nm absorption band of water vapor. Pulses of laser light are fired vertically below the aircraft. A small fraction of the transmitted laser light is reflected from the atmosphere back to the aircraft and collected with a telescope receiver. The received light indicates the amount of water vapor along the path of the laser beam.

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Syed Ismail (Prev PI)

Fast In-situ Stratospheric Hygrometer

The Fast In situ Stratospheric Hygrometer (FISH), developed at the Forschungszentrum Jülich (Germany), is based on the Lyman-a photofragment fluorescence technique. Details of the instrument and the calibration procedure are described in Zöger et al. [1999]. FISH has been used in several campaigns both from balloon and aircraft and compared with a large number of other hygrometers [Kley et al., 2000].

FISH consists of a closed, vacuum-tight fluorescence cell, a Lyman-a radiation source, a PMT in photon-counting mode, detectors to monitor the VUV radiation output of the Lyman-a lamp, and a mirror drive that controls the measuring cycle (see diagram): determination of the fluorescence and background count rate and of the lamp intensity. With a measurement frequency of 1 Hz, the noise equivalent mixing ratio at 3 ppmv is 0.2-0.15 ppmv, and the detection limit is 0.18-0.13 ppmv.

FISH is calibrated between flights in the laboratory using a calibration bench under realistic conditions, that is varying the H2O mixing ratio of the test air from a few ppmv to several hundred ppmv and the pressure from 1000 to 10 hPa. A frost point hygrometer is used as a reference instrument. The overall accuracy of FISH measurements is 5-6 %.

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