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CRYSTAL-FACE
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Forward Scattering Spectrometer Probe

The FSSP is of that general class of instruments called optical particle counters (OPCs) that detect single particles and size them by measuring the intensity of light that the particle scatters when passing through a light beam. A Helium Neon laser beam is focused to a diameter of 0.2 mm at the center of an inlet that faces into the oncoming airstream. This laser beam is blocked on the opposite side of the inlet with an optical stop, a "dump spot" to prevent the beam from entering the collection optics. Particles that encounter this beam scatter light in all directions and some of that scattered in the forward direction is directed by a right angle prism though a condensing lens and onto a beam splitter. The "dump spot" on the prism and aperture of the condensing lens define a collection angle from about 4º - 12º.

The beam splitter divides the scattered light into two components, each of which impinge on a photodetector. One of these detectors, however, is optically masked to receive only scattered light when the particles pass through the laser beam displaced greater than approximately 1.5 mm either side of the center of focus. Particles that fall in that region are rejected when the signal from the masked detector exceeds that from the unmasked detector. This defines the sample volume needed to calculate particle concentrations.

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Solar Spectral Flux Radiometer

In early 2000, the Ames Atmospheric Radiation Group completed the design and development of an all new Solar Spectral Flux Radiometer (SSFR). The SSFR is used to measure solar spectral irradiance at moderate resolution to determine the radiative effect of clouds, aerosols, and gases on climate, and also to infer the physical properties of aerosols and clouds. Additionally, the SSFR was used to acquire water vapor spectra using the Ames 25-meter base-path multiple-reflection absorption cell in a laboratory experiment. The Solar Spectral Flux Radiometer is a moderate resolution flux (irradiance) spectrometer with 8-12 nm spectral resolution, simultaneous zenith and nadir viewing. It has a radiometric accuracy of 3% and a precision of 0.5%. The instrument is calibrated before and after every experiment, using a NIST-traceable lamp. During field experiments, the stability of the calibration is monitored before and after each flight using portable field calibrators. Each SSFR consists of 2 light collectors, which are either fix-mounted to the aircraft fuselage, or on a stabilizing platform which counteracts the movements of the aircraft. Through fiber optic cables, the light collectors are connected to 2 identical pairs of spectrometers, which cover the wavelength range from (a) 350 nm-1000 nm (Zeiss grating spectrometer with Silicon linear diode array) and (b) 950 nm - 2150 nm (Zeiss grating spectrometer with InGaAs linear diode array). Each spectrometer pair covers about 95% of the incoming solar incident irradiance spectrum.

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SPP-100

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Video Ice Particle Sampler

The VIPS is an electro-optical instrument used to collect and record a continuous sample of cloud particles down to 5 um. Particles are collected continuously on a looped belt coated with silicone oil. The portion of the belt exposed to the airstream is imaged by two very high resolution charged coupled device (CCD) shuttered video cameras with different resolutions. The resulting imagery is available for real-time, in-flight evaluation of cloud conditions and for post-flight habit classification and spectra analysis.

The VIPS system is composed of two parts: (1) an electro-optical collection and imaging unit mounted in a standard particle measurement system (PMS) can, and (2) data acquisition and recording components. Aperture width of the collection subassembly is adjustable for varying flight conditions. The CCD imaging cameras are coupled with inline, high detail video enhancers. Particle imagery is recorded continuously at 30 Hz on high-resolution Hi-8 VCRs. Images are also captured at 1 Hz, digitized in real-time and recorded on an Apple PowerPC.

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Particle Analysis By Laser Mass Spectrometry

The NOAA PALMS instrument measures single-particle aerosol composition using UV laser ablation to generate ions that are analyzed with a time-of-flight mass spectrometer.  The PALMS size range is approximately 150 to >3000 nm and encompasses most of the accumulation and coarse mode aerosol volume. Individual aerosol particles are classified into compositional classes.  The size-dependent composition data is combined with aerosol counting instruments from Aerosol Microphysical Properties (AMP), the Langley Aerosol Research Group Experiment (LARGE), and other groups to generate quantitative, composition-resolved aerosol concentrations.  Background tropospheric concentrations of climate-relevant aerosol including mineral dust, sea salt, and biomass burning particles are the primary foci for the ATom campaigns.  PALMS also provides a variety of compositional tracers to identify aerosol sources, probe mixing state, track particle aging, and investigate convective transport and cloud processing.

*_Standard data products_**: *

Particle type number fractions: sulfate/organic/nitrate mixtures, biomass burning, EC, sea salt, mineral dust, meteoric, alkali salts, heavy fuel combustion, and other. Sampling times range from 1-5 mins.

*_Advanced data products_**:*

Number, surface area, volume, and mass concentrations of the above particle types. Total sulfate and organic mass concentrations. Relative and absolute abundance of various chemical markers and aerosol sub-components: methanesulfonic acid, sulfate acidity, organic oxidation level, iodine, bromine, organosulfates, pyridine, and other species.

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National Airborne Sounder Testbed - Interferometer

The National Airborne Sounder Testbed-Interferometer (NAST-I) is a high spectral resolution (0.25 cm-1) and high spatial resolution (0.13 km linear resolution per km of aircraft flight altitude, at nadir) scanning (2.3 km ground cross-track swath width per km of aircraft flight altitude) passive infrared (IR) Michelson interferometer sounding system that was developed to be flown on high-altitude aircraft to provide experimental observations needed to finalize the specifications and to test proposed designs and data processing algorithms for the Cross-track Infrared Sounder (CrIS) flying on the Suomi NPP (SNPP) and Joint Polar Satellite System (JPSS) platforms. Because the NAST-I infrared spectral radiance and temperature, humidity, trace species, cloud and surface property soundings have unprecedented spectral and high spatial resolution, respectively, the data can be used to support a variety of satellite sensor calibration / validation and atmospheric research programs. The NAST-I covers a spectral range from ~ 600-2900 cm-1 (3.5-16 microns) with 0.25 cm-1 spectral resolution, yielding more than 9000 spectral channels of radiance emission/absorption information. The NAST-I instrument has flown numerous science missions on the ER-2, WB-57, and Proteus aircraft, and the team has evaluated efforts needed to become operational on the DC-8. Most recently, NAST-I was part of the ER-2 science payload for the FIREX-AQ field campaign conducted during August, 2019 (https://www.esrl.noaa.gov/csl/projects/firex-aq/). Additional information can be obtained from Anna Noe (anna.m.noe@nasa.gov, 757-864-6466), Dr. Daniel Zhou (daniel.k.zhou@nasa.gov, 757-864-5663), or Dr. Allen Larar (Allen.M.Larar@nasa.gov, 757-864-5328).

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Anna Noe (Mgr)

PAN and Trace Hydrohalocarbon ExpeRiment

PANTHER uses Gas Chromatography with Electron Capture Detection and (GC-ECD) and Gas Chromatography with Mass Selective Detection (GC-MSD) to measure numerous trace gases, including methyl halides, HCFCs, peroxyacetyl nitrate, nitrous oxide, SF6, CFC-12, CFC-11, Halon-1211, methyl chloroform, carbon tetrachloride.

3 ECDs with packed columns (OV-101, Porapak-Q, molecular sieve).

1 ECD with a TE (thermal electric) cooled RTX-200 capillary column.

2-channel MSD (mass selective detector). The MSD analyzes two independent samples air concentrated onto TE cooled Haysep traps, which are then heated to desorb the analytes and separate using through two temperature programmed RTX-624 capillary columns.

With the exception of PAN, all channels of chromatography are normalized to a stable in-flight calibration gas references to NOAA scales. The PAN data are normalized to an in-flight PAN source of ≈ 100 ppt with ±5 % reproducibility. This source is generated by efficient photolytic conversion of NO in the presence of acetone. Detector non-linearity is taken out by lab calibrations for all molecules.

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Dual-Beam UV-Absorption Ozone Photometer

The NOAA-O3 instrument consists of a mercury lamp, two sample chambers that can be periodically scrubbed of ozone, and two detectors that measure the 254-nm radiation transmitted through the chamber. The ozone absorption cross-section at this wavelength is accurately known; hence, the ozone number density can be easily calculated. Since the two absorption chambers are identical, virtually continuous measurements of ozone are made by alternating the ambient air sample and ozone scrubbed sample between the two chambers. At a one-second data collection rate, the minimum detectable concentration of ozone (one standard deviation) is 1.5 x 10 10 molecules/cm 3 (0.6ppbv at STP).

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Radiometric Measurement System

Optics: We employed very simple optical arrangement for the radiometer. The diffuser-light trap arrangement provides a hemispherical field of view with incident radiation being collimated by the high reflectance walls of the exponential-logarithmic cavity. Enough collimation of the radiation is achieved with this design that narrow spectral bandpass interference filters can be used to select desired wavelength regions.

Electronics: The instrument electronics includes five major functional blocks. They are the detectors signal conditioning block, the data processing block, the system controller block, the shadow ring drive and control block, and the data storage block.

The signal detectors are silicon photodiodes operating in the photovoltaic mode and covering the spectral range from about 0.3 to 1.1µm. Their signals are converted into electrical voltages by low noise FET input operational amplifiers. Programmable gain amplifiers allow adjustments for dynamic range, and filter circuits condition the signals for analog to digital processing. Data processing units consist of an analog multiplexer circuit, a sample-and-hold circuit, and an analog to digital converter providing a 12-bit resolution output. The shadow ring is driven by a DC motor rotating at a constant speed. A motor controller is used to maintain motor speed. The system controller provides the timing necessary to perform all the system's tasks. It sets the shadow ring in motion and steps through the detector's outputs, maintaining the proper dynamic range for the analog to digital converter by selecting the proper amplifier gain. It also controls the analog to digital conversion and selectively stores data.

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Microwave Temperature Profiler

The Microwave Temperature Profiler (MTP) is a passive microwave radiometer, which measures the natural thermal emission from oxygen molecules in the earth’s atmosphere for a selection of elevation angles between zenith and nadir. The current observing frequencies are 55.51, 56.65 and 58.80 GHz. The measured "brightness temperatures" versus elevation angle are converted to air temperature versus altitude using a quasi-Bayesian statistical retrieval procedure. The MTP has no ITAR restrictions, has export compliance classification number EAR99/NLR. An MTP generally consists of two assemblies: a sensor unit (SU), which receives and detects the signal, and a data unit (DU), which controls the SU and records the data. In addition, on some platforms there may be a third element, a real-time analysis computer (RAC), which analyzes the data to produce temperature profiles and other data products in real time. The SU is connected to the DU with power, control, and data cables. In addition the DU has interfaces to the aircraft navigation data bus and the RAC, if one is present. Navigation data is needed so that information such as altitude, pitch and roll are available. Aircraft altitude is needed to perform retrievals (which are altitude dependent), while pitch and roll are needed for controlling the position of a stepper motor which must drive a scanning mirror to predetermined elevation angles. Generally, the feed horn is nearly normal to the flight direction and the scanning mirror is oriented at 45-degrees with respect to receiving feed horn to allow viewing from near nadir to near zenith. At each viewing position a local oscillator (LO) is sequenced through two or more frequencies. Since a double sideband receiver is used, the LO is generally located near the "valley" between two spectral lines, so that the upper and lower sidebands are located near the spectral line peaks to ensure the maximum absorption. This is especially important at high altitudes where "transparency" corrections become important if the lines are too "thin." Because each frequency has a different effective viewing distance, the MTP is able to "see" to different distances by changing frequency. In addition, because the viewing direction is also varied and because the atmospheric opacity is temperature and pressure dependent, different effective viewing distances are also achieved through scanning in elevation . If the scanning is done so that the applicable altitudes (that is, the effective viewing distance times the sine of the elevation angle) at different frequencies and elevation angles are the same, then inter-frequency calibration can also be done, which improves the quality of the retrieved profiles. For a two-frequency radiometer with 10 elevation angles, each 15-second observing cycle produces a set of 20 brightness temperatures, which are converted by a linear retrieval algorithm to a profile of air temperature versus altitude, T(z). Finally, radiometric calibration is performed using the outside air temperature (OAT) and a heated reference target to determine the instrument gain. However, complete calibration of the system to include "window corrections" and other effects, requires tedious analysis and comparison with radiosondes near the aircraft flight path. This is probably the most important single factor contributing to reliable calibration. For stable MTPs, like that on the DC8, such calibrations appear to be reliable for many years. Such analysis is always performed before MTP data are placed on mission archive computers.

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DC-8 - AFRC, ER-2 - AFRC, Global Hawk - AFRC, L-188C, M-55, Gulfstream V - NSF, WB-57 - JSC
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