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Synonyms: 
SEACARS
SEA4CRS
SEACR4S
SEAC<sup>4</sup>RS
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Charged-coupled device Actinic Flux Spectroradiometers

The Charged-coupled device Actinic Flux Spectroradiometers (CAFS) instruments measure in situ down- and up-welling radiation and combine to provide 4 pi steradian actinic flux density spectra from 280 to 650 nm. The sampling resolution is ~0.8 nm with a full width at half maximum (FWHM) of 1.7 nm at 297 nm. From the measured flux, photolysis frequencies are calculated for ~40 important atmospheric trace gases including O3, NO2, HCHO, HONO and NO3 using a modified version of the NCAR Tropospheric Ultraviolet and Visible (TUV) radiative transfer model. The absolute spectral sensitivity of the instruments is determined in the laboratory with 1000 W NIST-traceable tungsten-halogen lamps with a wavelength dependent uncertainty of 3–5%. During deployments, spectral sensitivity is assessed with secondary calibration lamps while wavelength assignment is tracked with Hg line sources and comparisons to spectral features in the extraterrestrial flux. The optical collectors are characterized for angular and azimuthal response and the effective planar receptor distance. CAFS have an excellent legacy of performance on the NASA DC-8 and WB-57 platforms during atmospheric chemistry and satellite validation mission. These include AVE Houston 2004 and 2005, PAVE, CR-AVE, TC4, ARCTAS, DC3, SEAC4RS, KORUS-AQ, ATom and FIREX-AQ. For FIREX-AQ, upgraded electronics and cooling reduced noise and allowed for a decrease to 1 Hz acquisition.

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Chemical Ionization Mass Spectrometer

The single mass analyzer CIMS (S-CIMS) was developed for use on NASA’s ER-2 aircraft. Its first measurements were made in 2000 (SOLVE, see photo). Subsequently, it has flown on the NASA DC-8 aircraft for INTEX-NA, DICE, TC4, ARCTAS, ATom, KORUS, FIREX, as well as on the NCAR C-130 during MILAGRO/INTEX-B. HNO3 is measured by selective ion chemical ionization via the fluoride transfer reaction: CF3O- + HNO3 → HF • NO3- + CF2O In addition to its fast reaction rate with HNO3, CF3O- can be used to measure additional acids and nitrates as well as SO2 [Amelynck et al., 2000; Crounse et al., 2006; Huey et al., 1996]. We have further identified CF3O- chemistry as useful for the measurement of less acidic species via clustering reactions [Crounse et al., 2006; Paulot et al., 2009a; Paulot et al., 2009b; St. Clair et al., 2010]: CF3O- + HX → CF3O- • HX where, e.g., HX = HCN, H2O2, CH3OOH, CH3C(O)OOH (PAA) The mass analyzer of the S-CIMS instrument was first upgraded from a quadrupole to a unit-mass resolution time-of-flight (ToF) analyzer. In 2023, the mass filter was again upgraded to an 1m flight path (~5000 deltaM/M).  The ToF admits the sample ion beam to the ion extractor, where a pulse of high voltage orthogonally deflects and accelerates the ions into the reflectron, which in turn redirects the ions toward the multichannel plate detector. Ions in the ToF follow a V-shaped from the extractor to detector, separating by mass as the smaller ions are accelerated to greater velocities by the high voltage pulse. The detector collects the ions as a function of time following each extractor pulse. The rapid-scan collection of the ToF guarantees a high temporal resolution (1 Hz or faster) and simultaneous data products from the S-CIMS instrument for all mass channels [Drewnick et al., 2005]. We have flown a tandem CIMS (TCIMS) instrument in addition to the SCIMS since INTEX-B (2006). The T-CIMS provides parent-daughter mass analysis, enabling measurement of compounds precluded from quantification by the S-CIMS due to mass interferences (e.g. MHP) or the presence of isobaric compounds (e.g. isoprene oxidation products) [Paulot et al., 2009b; St. Clair et al., 2010]. Calibrations of both CIMS instruments are performed in flight using isotopically-labeled reagents evolved from a gas cylinders or from a thermally-stabilized permeation tube oven [Washenfelder et al., 2003]. By using an isotopically labeled standard, the product ion signals are distinct from the natural analyte and calibration can be performed at any time without adversely affecting the ambient measurement.

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14-channel NASA Ames Airborne Tracking Sunphotometer

AATS-14 measures direct solar beam transmission at 14 wavelengths between 354 and 2139 nm in narrow channels with bandwidths between 2 and 5.6 nm for the wavelengths less than 1640 nm and 17.3 nm for the 2139 nm channel. The transmission measurements at all channels except 940 nm are used to retrieve spectra of aerosol optical depth (AOD). In addition, the transmission at 940 nm and surrounding channels is used to derive columnar water vapor (CWV) [Livingston et al., 2008]. Methods for AATS-14 data reduction, calibration, and error analysis have been described extensively, for example, by Russell et al. [2007] and Shinozuka et al. [2011]. AATS-14 measurements of spectral AOD and CWV obtained during aircraft vertical profiles can be differentiated to determine corresponding vertical profiles of spectral aerosol extinction and water vapor density. Such measurements have been used extensively in the characterization of the horizontal and vertical distribution of aerosol optical properties and in the validation of satellite aerosol sensors. For example, in the Aerosol Characterization Experiment-Asia (ACE-Asia), AATS measurements were used for closure (consistency) studies with in situ aerosol samplers aboard the NCAR C-130 and the CIRPAS Twin-Otter aircraft, and with ground-based lidar systems. In ACE-Asia, CLAMS (Chesapeake Lighthouse & Aircraft Measurements for Satellites, 2001), the Extended-MODIS-λ Validation Experiment (EVE), INTEX-A, INTEX-B, and ARCTAS, AATS results have been used in the validation of satellite sensors aboard various EOS platforms, providing important aerosol information used in the improvement of retrieval algorithms for the MISR and MODIS sensors among others.

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DC-8 - AFRC, J-31, P-3 Orion - WFF, Convair 580 NRC, Twin Otter International, C130H - WFF
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Airborne Multi-angle SpectroPolarimeter Imager

The Multiangle SpectroPolarimetric Imager, or AirMSPI, was a candidate for the multi-directional, multi-wavelength, high-accuracy polarization imager identified by the National Research Council's Earth Sciences Decadal Survey as one component of the notional Aerosol-Cloud-Ecosystem, or ACE, mission. The ACE spacecraft was planned to characterize the role of aerosols in climate forcing, especially their impact on precipitation and cloud formation. Forcing is the process by which natural mechanisms or human activities alter the global energy balance and “force” the climate to change. The unresolved effects of aerosols on clouds are among the greatest uncertainties in predicting global climate change. AirMSPI is conceptually similar to JPL’s Multiangle Imaging SpectroRadiometer, or MISR, carried on NASA’s EOS Terra spacecraft, but with some important additions. The new camera design extends the spectral range to the ultraviolet and shortwave infrared (from 446–866 nm to 355–2130 nm), increases the image swath (from 360 km to 680 km) to achieve more rapid global coverage (from 9 days to 4 days), and adds high-accuracy polarimetry in selected spectral bands. Like MISR, a suite of AirMSPI cameras would view Earth at a variety of angles, with an intrinsic pixel size of a few hundred meters, which for certain channels would be averaged up to about 1 kilometer.
An advanced version of this instrument is currently in development, called AirMSPI-2. 

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2D-S Stereo Probe

The 2D-S Stereo Probe is an optical imaging instrument that obtains stereo cloud particle images and concentrations using linear array shadowing. Two diode laser beams cross at right angles and illuminate two linear 128-photodiode arrays. The lasers are single-mode, temperature-stabilized, fiber-coupled diode lasers operating at 45 mW. The optical paths are arbitrarily labeled the “vertical” and “horizontal” probe channels, but the verticality of each channel actually depends on how the probe is oriented on an aircraft. The imaging optical system is based on a Keplerian telescope design having a (theoretical) primary system magnification of 5X, which results in a theoretical effective size of (42.5 µm + 15 µm)/5 = 11.5 µm. However, actual lenses and arrays have tolerances, so it is preferable to measure the actual effective pixel size by dropping several thousands of glass beads with known diameters through the object plane of the optics system.

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Aircraft Laser Infrared Absorption Spectrometer

ALIAS (Aircraft Laser Infrared Absorption Spectrometer) measures total water, total water isotopes, carbon monoxide, and carbon dioxide isotope ratios. No other instrument provides real-time measurements of carbon dioxide isotope ratios which are clear identifiers of atmospheric transport (18O/17O/16O for stratospheric intrusion, 13C/12C for anthropogenic signals). ALIAS easily adapts to changing mission priorities and can be configured to measure HCl, CH4, SO2, and N2O by simply replacing a semiconductor laser. These measurements contribute to Atmospheric Composition Focus Area research by providing key data on how convective processes affect stratospheric composition, the development of cirrus particles and their affect on Earth's radiative balance, and health of the ozone layer through measurement of chlorine partitioning.

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