NASA - National Aeronautics and Space Administration

The Cloud Physics Lidar, or CPL, is a backscatter lidar designed to operate simultaneously at 3 wavelengths: 1064, 532, and 355 nm. The purpose of the CPL is to provide multi-wavelength measurements of cirrus, subvisual cirrus, and aerosols with high temporal and spatial resolution. Figure 1 shows the entire CPL package in flight configuration. The CPL utilizes state-of-the-art technology with a high repetition rate, low pulse energy laser and photon-counting detection. Vertical resolution of the CPL measurements is fixed at 30 m; horizontal resolution can vary but is typically about 200 m. The CPL fundamentally measures range-resolved profiles of volume 180-degree backscatter coefficients. From the fundamental measurement, various data products are derived, including: time-height crosssection images; cloud and aerosol layer boundaries; optical depth for clouds, aerosol layers, and planetary boundary layer (PBL); and extinction profiles. The CPL was designed to fly on the NASA ER-2 aircraft but is adaptable to other platforms. Because the ER-2 typically flies at about 65,000 feet (20 km), onboard instruments are above 94% of the earth’s atmosphere, allowing ER-2 instruments to function as spaceborne instrument simulators. The ER-2 provides a unique platform for atmospheric profiling, particularly for active remote sensing instruments such as lidar, because the spatial coverage attainable by the ER-2 permits studies of aerosol properties across wide regions. Lidar profiling from the ER-2 platform is especially valuable because the cloud height structure, up to the limit of signal attenuation, is unambiguously measured.

The in‐situ diode laser spectrometer system, referred to by its historical name DACOM, includes three tunable diode lasers providing 4.7, 4.5, and 3.3 μm radiation for accessing CO, N2O, and CH4 absorption lines, respectively. The three laser beams are combined by the use of dichroic filters and are then directed through a small volume (0.3 liter) Herriott cell enclosing a 36 meter optical path. As the three coincident laser beams exit the absorption cell, they are spectrally isolated using dichroic filters and are then directed to individual detectors, one for each laser wavelength. Wavelength reference cells containing CO, CH4, and N2O are used to wavelength lock the operation of the three lasers to the appropriate absorption lines. Ambient air is continuously drawn through a Rosemount inlet probe and a permeable membrane dryer which removes water vapor before entering the Herriott cell and subsequently being exhausted via a vacuum pump to the aircraft cabin. To minimize potential spectral overlap from other atmospheric species, the Herriott cell is maintained at a reduced pressure of ~90 Torr. At 5 SLPM mass flow rate, the absorption cell volume is exchanged nominally twice per second. Frequent but short calibrations with well documented and stable reference gases are critical to achieving both high precision and accuracy. Calibration for all species is accomplished by periodically (~4 minutes) flowing calibration gas through this instrument. Measurement accuracy is closely tied to the accuracy of the reference gases obtained from NOAA/ESRL, Boulder, CO. Both CO and CH4 mixing ratios are provided in real-time to investigators aboard the DC‐8.

Two spectrographs + HD video camera
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Air Quality (AQ) 304:520 nm 0.8 nm resolution (NO2, O3, UV absorbing aerosols, SO2, HCHO)
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Ocean Color (OC) 460:900 nm 1.5 nm resolution
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Video camera (2592x1936 pixels) –3 pixel FWHM

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.

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.

Developed by Droplet Measurement Technologies, the CFSTGC is based on a concept by Roberts and Nenes [2005]. The instrument counts the fraction of aerosol particles that become droplets when exposed to a given water vapor supersaturation (RH > 100%).

As with all CCN counters, a temperature gradient is applied to produce a supersaturation of water vapor. However, the mechanism for generating supersaturation is not the same for all CCN counters. For example, for continuous flow parallel plate diffusion chambers, the temperature gradient is perpendicular to the flow, and supersaturation is a result of the nonlinear dependence of vapor pressure upon temperature. The same mechanism applies for static diffusion cloud chambers, where there is no flow at all.

However, as the name implies, for the Continuous Flow Streamwise Thermal Gradient CCN Counter, the temperature gradient is in the streamwise direction (maintained by thermoelectric coolers). In this case, supersaturation results as a consequence of the greater rate of mass transfer over heat transfer.

With laminar flow, heat and water vapor are transferred to the centerline of the column from the walls only by diffusion.

Since molecular diffusivity is greater than thermal diffusivity, the distance downstream that a water molecule travels before reaching the centerline is less than the distance the heat travels downstream before reaching the centerline. If you pick a point at the centerline, the heat originated from a greater distance upstream than the water vapor.

There are four facts that are necessary to explain how supersaturation is generated within the CFSTGC:

1) Assuming that the inner surface of the column is saturated with water vapor at all points, since the temperature is greater at point B than at point A, the water vapor partial pressure is also greater at point B than at point A.

2) The actual partial pressure of water vapor at point C is equal to the partial pressure of water vapor at point B.

3) However, since the temperature at point C is the same as at point A, the equilibrium water vapor pressure at point C is equal to the water vapor partial pressure at point A.

4) The saturation ratio is the ratio between the actual partial pressure of water vapor and the equilibrium vapor pressure. This is equivalent to the partial pressure at point B divided by the partial pressure at point A, which is always greater than one. Thus supersaturation is generated through a dynamic equilibrium.

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. 

The NOAA chemical ionization mass spectrometer (CIMS) instrument was developed for high-precision measurements of gaseous nitric acid (HNO3) specifically under high- and variable-humidity conditions in the boundary layer. The instrument’s background signals (i.e., signals detected when HNO3-free air is measured), which depend on the humidity and HNO3 concentration of the sample air, are the most important factor affecting the limit of detection (LOD). A new system to provide HNO3-free air without changing both the humidity and the pressure of the sampled air was developed to measure the background level accurately. The detection limit was about 23 parts per trillion by volume (pptv) for 50-s averages. Field tests, including an intercomparison with the diffusion scrubber technique, were carried out at a surface site in Tokyo, Japan, in October 2003 and June 2004. A comparison between the measured concentrations of HNO3 and particulate nitrate indicated that the interference from particulate nitrate was not detectable (i.e., less than about 1%). The intercomparison indicated that the two independent measurements of HNO3 agreed to within the combined uncertainties of these measurements.

AVIRIS is the second in a series of imaging spectrometer instruments developed at the Jet Propulsion Laboratory (JPL) for earth remote sensing. It is a unique optical sensor that delivers calibrated images of the upwelling spectral radiance in 224 contiguous spectral channels (bands) with wavelengths from 380 to 2510 nanometers. It uses scanning optics and four spectrometers to image a 677 pixel swath simultaneously in all 224 bands. AVIRIS has flown in North America, Europe, and portions of South America.

The AVIRIS sensor collects data that can be used for characterization of the Earth's surface and atmosphere from geometrically coherent spectroradiometric measurements. This data can be applied to studies in the fields of oceanography, environmental science, snow hydrology, geology, volcanology, soil and land management, atmospheric and aerosol studies, agriculture, and limnology. Applications under development include the assessment and monitoring of environmental hazards such as toxic waste, oil spills, and land/air/water pollution. With proper calibration and correction for atmospheric effects, the measurements can be converted to ground reflectance data which can then be used for quantitative characterization of surface features.