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ER-2
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Composition and Photo-Dissociative Flux Measurement

The instrument used for the CPFM is a spectroradiometer based on a concave, holographic diffraction grating and a 1024-element diode array detector. It measures the intensities of the two linear polarization components of radiation propagating upward at the aircraft location from a range of elevation angles near the horizon. In addition, a measurement of the intensity of the direct solar beam is made by viewing a horizontal diffusing surface mounted under a quartz dome on board the aircraft. These measurements are used to verify atmospheric light-scattering calculations, which are essential for the accurate modeling of the chemistry of the stratosphere where POLARIS makes its measurements.

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Condensation Nuclei Counter

The CNC counts particles in the approximate diameter range from 0.006 m to 2 m. The instrument operates by exposing the articles to saturated Flourinert vapor at 28 C and then cooling the sample in a condenser at 5 C. The supersaturation of the vapor increases as it is cooled and the vapor condenses on the particles causing them to grow to sizes which are easily detected. The resulting droplets are passed through a laser beam and the scattered light is detected. Individual particles are counted and are referred to as condensation nuclei (CN). Two CN Counters are provided in the instrument. One counts the particles after sampling from the atmosphere and the second counts particles that have survived heating to 192C. Lab experiments show that pure sulfuric acid particles smaller than 0.05 mm are volatilized in the heater. The heated channel detects when small particles are volatile and permits speculation about the composition. The CNC II contains an impactor collector which permits the collection of particles on electron microscope grids for later 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 collect efficiently even at small Reynolds numbers. The system collects particles as small as 0.02 m at WB-57 cruise altitudes. As many as 25 samples can be collected in a flight.

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BroadBand Radiometers

The Broadband Radiometers (BBR) consist of modified Kipp & Zonen CM-22 pyranometers (to measure solar irradiance) and CG-4 pyrgeometers (to measure IR irradiance) (see http://www.kippzonen.com/). The modifications to make these instruments more suitable for aircraft use include new instrument housings and amplification of the signal at the sensor. The instruments are run in current-loop mode to minimize the effects of noise in long signal cables. The housing is sealed and evacuated to prevent condensation or freezing inside the instrument. Each BBR has the following properties: Field-of-view: Hemispheric Temperature Range: -65C to +80C Estimated Accuracy: 3-5% Data Rate: 1Hz

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GeoCAPE Airborne Spectrometer

Two spectrographs + HD video camera

Air Quality (AQ) 304:520 nm 0.8 nm resolution (NO2, O3, UV absorbing aerosols, SO2, HCHO)

Ocean Color (OC) 460:900 nm 1.5 nm resolution

Video camera (2592x1936 pixels) –3 pixel FWHM

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Next-Generation Airborne Visible/Infrared Imaging Spectrometer

The NASA Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) has been in operation since 1989 acquiring contiguous spectral measurements between 380 and 2510 nm for use by a range of terrestrial ecology science investigations related to: (1) pattern and spatial distribution of ecosystems and their components, (2) ecosystem function, physiology and seasonal activity, (3) biogeochemical cycles, (3) changes in disturbance activity, and (4) ecosystems and human health. While AVIRIS continue to make unique and significant science contributions, such as its deployment to the Gulf of Louisiana in May 2010 for the assessment of the amount of oil spilled by the offshore well, the need for a new sensor to share AVIRIS’ workload and to eventually replace AVIRIS is inevitable. Indeed, since the late summer of 2009 a new NASA Earth Science airborne sensor called the Next Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRISng) is being developed by JPL through the funding support from the American Recovery and Reinvestment Act (ARRA). The technical and programmatic oversights of the AVIRISng development is provided by NASA’s Earth Science Technology Office (ESTO).

Similar to its predecessor, the AVIRIS-NG is being designed to be compatible with a broad array of possible aircraft platforms, such as NASA’s ER-2 jet, the Twin Otter turboprop, B200 King Air, and NASA’s Gulfstream III and V.

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ER-2 - AFRC, Twin Otter, Gulfstream III - LaRC, Gulfstream G-5
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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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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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Advanced Microwave Precipitation Radiometer

The AMPR is a total power passive microwave radiometer producing calibrated brightness temperatures (TB) at 10.7, 19.35, 37.1, and 85.5 GHz. These frequencies are sensitive to the emission and scattering of precipitation-size ice, liquid water, and water vapor. The AMPR performs a 90º cross-track data scan perpendicular to the direction of aircraft motion. It processes a linear polarization feed with full vertical polarization at -45º and full horizontal polarization at +45º, with the polarization across the scan mixed as a function of sin2, giving an equal V-H mixture at 0º (aircraft nadir). A full calibration is made every fifth scan using hot and cold blackbodies. From a typical ER-2 flight altitude of ~20 km, surface footprint sizes range from 640 m (85.5 GHz) to 2.8 km (10.7 GHz). All four channels share a common measurement grid with collocated footprint centers, resulting in over-sampling of the low frequency channels with respect to 85.5 GHz.

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Argus Tunable Diode Laser Instrument

Argus is a two channel, tunable diode laser instrument set up for the simultaneous, in situ measurement of CO (carbon monoxide), N2O (nitrous oxide) and CH4 (methane) in the troposphere and lower stratosphere. The instrument measures 40 x 30 x 30 cm and weighs 21 kg. An auxiliary, in-flight calibration system has dimensions 42 x 26 x 34 cm and weighs 17 kg.

The instrument is an absorption spectrometer operating in rapid scan, secondharmonic mode using frequency-modulated tunable lead-salt diode lasers emitting in the mid-infrared. Spectra are co-added for two seconds and are stored on a solid state disk for later analysis. The diode laser infrared beam is shaped by two anti-refection coated lenses into an f/40 beam focused at the entrance aperture of a multi-pass Herriott cell. The Herriott cell is common to both optical channels and is a modified astigmatic cell (New Focus Inc., Santa Clara, California).

The aspherical mirrors are coated with protected silver for optimal infrared reflectivity. The cell is set up for a 182-pass state for a total path of 36m. The pass number can be confirmed by visual spot pattern verification on the mirrors observed through the glass cell body when the cell is illuminated with a visible laser beam. However, instrument calibration is always carried out using calibrated gas standards with the Argus instrument operating at its infrared design wavelengths, 3.3 and 4.7 micrometers respectively for CH4 and CO detection. The electronic processing of the second harmonic spectra is done by standard phase sensitive amplifier techniques with demodulation occurring at twice the laser modulation frequency of 40 kHz. To optimize the secondharmonic signal amplitude in a changing ambient pressure environment the laser modulation amplitude is updated every 2 seconds to its optimal theoretical value based upon the measured pressure in the Herriott cell.

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Airborne Tunable Laser Absorption Spectrometer

ATLAS uses a tunable laser to detect an infrared-active target gas such as N2O, methane, carbon monoxide, or ozone. The laser source is tuned to an individual roto-vibrational line in an infrared absorption band of the target gas, and is frequency modulated at 2 kHz. The instrument detects the infrared target gas by measuring the fractional absorption of the infrared beam from the tunable diode laser as it traverses a multipass White cell containing an atmospheric sample at ambient pressure.

Synchronous detection of the resultant amplitude modulation at 2kHz and 4kHz yields the first and second harmonics of the generally weak absorption feature with high sensitivity (DI/I < 1E-5). Part of the main beam is split off through a short cell containing a known amount of the target gas to a reference detector. The reference first harmonic signal is used to lock the laser frequency to the absorption line center, while the second harmonic signal is used to derive the calibration factor needed to convert the measurement beam second harmonic amplitude into absolute gas concentration. A zero beam is included to correct for background gas absorption occurring outside the multipass cell. The response time of the instrument is set by the gas flow rate through the White cell, which is normally adjusted to give a new sample every second. Periodic standard additions of the target gas are injected into the sample stream as a second method to calibrate the measurement technique and as an overall instrument diagnostic.

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