WB-57 - JSC

The nucleation-mode aerosol size spectrometer (NMASS) measures the concentration of particles as a function of diameter from approximately 4 to 60 nm. A sample flow is continuously extracted from the free stream using a decelerating inlet and is transported to the NMASS. Within the instrument, the sample flow is carried to 5 parallel condensation nucleus counters (CNCs) as shown in Fig. 1. Each CNC is tuned to measure the cumulative concentration of particles larger than certain diameter. The minimum detectable diameters for the 5 CNCs are 4.0, 7.5, 15, 30 and 55 nm, respectively. An inversion algorithm is applied to recover a continuous size distribution in the 4 to 60 nm diameter range.

The NMASS has been proven particularly useful in measurements of nucleation-mode size distribution in environments where concentrations are relatively high and fast instrumental response is required. The instrument has made valuable measurements vicinity of cirrus clouds in the upper troposphere and lower stratosphere (WAM), in the near-field exhaust of flying aircraft (SULFUR 6), in newly created rocket plumes (ACCENT), and in the plumes of coal-fired power plants (SOS ’99). The instrument has flown on 3 different aircraft and operated effectively at altitudes from 50 m to 19 km and ambient temperatures from 35 to -80ºC.

Accuracy. The instrument is calibrated using condensationally generated particles that are singly charged and classified by differential electrical mobility. Absolute counting efficiencies are determined by comparison with an electrometer. Monte carlo simulations of the propagation of uncertainties through the numerical inversion algorithm and comparison with established laboratory techniques are used to establish accuracies for particular size distributions, and may vary for different particle size distributions. A study of uncertainties in aircraft plume measurements demonstrated a combined uncertainty (accuracy and precision) of 38%, 36% and 38% for number, surface and volume, respectively.

Precision. The precision is controlled by particle counting statistics for each channel. If better precision is desired, it is necessary only to accumulate over longer time intervals.

Response Time: Data are recorded with 10 Hz resolution, and the instrument has demonstrated response times of this speed in airborne sampling. However the effective response time depends upon the precision required to detect the change in question. Small changes may require longer times to detect. Plume measurements with high concentrations of nucleation-mode particles may be processed at 10 Hz.

Specifications: Weight is approximately 96 lbs, including an external pump. External dimensions are approximately 15”x16”x32”. Power consumption is 350 W at 28 VDC, including the pump.

NIRAD consists of three systems: (1) CO2 detector, (2) power and data acquisition, and (3) gas-handling. All three systems have flown previously. The CO2 detector was first flown in 1999 as part of CORE+ instrument during RISO and ACCENT and again in 2004 during PUMA-A. There have been no changes to the detector, other than inspection and routine maintenance. The power and data acquisition system were new for PUMA-A, and are flown here without change, other than to software. The gas-handling system is the same as that flown in May 2004, except that it is now packaged into a single box that contains the detector and power/data system.

The detector is packaged in a vacuum housing to facilitate management of temperature and pressure. At power-up the housing is pumped down to ~300 hPa by one stage of a diaphragm pump and held at this pressure throughout the flight. Thus, at pressure altitudes < 300 hPa the pressure within the housing is above ambient. By design, if the pressure differential is significantly greater than about 5 psi, the O-ring seals leak. A redundant additional mechanical safety relief valve (set for ~15 psi or less) is placed on the housing.

Two 1.2 L epoxy-coated, fiber-wrapped aluminum bottles (DOT rated and certified) are filled to ~1600 psi before flight with zero air doped with CO2. These ‘standards’ are sampled repeatedly during flight to provide an accurate standard for reference to the NOAA/CMDL CO2 scale. Two-stage regulators provide a service pressure of ~25-30 psig throughout flight. The bottles and regulators are backed with safety relief valves.

The diaphragm pump is current-limited for a ‘soft start’ (that is, there is no electrical surge on startup, allowing for use of compact, highly efficient Vicor VI-100 DC/DC converters.

The NAST-M currently consists of two radiometers covering the 50-57 GHz band and a set of spectral emission measurements within 4 GHz of the 118.75 GHz oxygen line with eight single sideband and 9 double sideband channels, respectively. To be added prior to CRYSTAL-FACE are five double side band channels within 4 GHz of the 183 GHz water vapor line and a single band channel at 425 GHz. For clear air, the temperature and water vapor information provided by the 50-57 GHz, 118 GHz, and 183 GHz channels is largely redundant; but, for cloudy sky conditions the three bands provide information on the effects of precipitating clouds on the temperature and water vapor profile retrievals and enables sounding through the non-precipitating portion of the cloud, a feature particularly important for CRYSTAL-FACE.

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).

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.

The Meteorological Measurement System (MMS) is a state-of-the-art instrument for measuring accurate, high resolution in situ airborne state parameters (pressure, temperature, turbulence index, and the 3-dimensional wind vector). These key measurements enable our understanding of atmospheric dynamics, chemistry and microphysical processes. The MMS is used to investigate atmospheric mesoscale (gravity and mountain lee waves) and microscale (turbulence) phenomena. An accurate characterization of the turbulence phenomenon is important for the understanding of dynamic processes in the atmosphere, such as the behavior of buoyant plumes within cirrus clouds, diffusions of chemical species within wake vortices generated by jet aircraft, and microphysical processes in breaking gravity waves. Accurate temperature and pressure data are needed to evaluate chemical reaction rates as well as to determine accurate mixing ratios. Accurate wind field data establish a detailed relationship with the various constituents and the measured wind also verifies numerical models used to evaluate air mass origin. Since the MMS provides quality information on atmospheric state variables, MMS data have been extensively used by many investigators to process and interpret the in situ experiments aboard the same aircraft.

The MASTER is similar to the MAS, with the thermal bands modified to more closely match the NASA EOS ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite instrument, which was launched in 1998. It is intended primarily to study geologic and other Earth surface properties. Flying on both high and low altitude aircraft, the MASTER has been operational since early 1998.

Instrument Type: Multispectral Imager
Measurements: VNIR/SWIR/MWIR/LWIR Imagery

The MASTER is similar to the MAS, with the thermal bands modified to more closely match the NASA EOS ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite instrument, which was launched in 1998. It is intended primarily to study geologic and other Earth surface properties. Flying on both high and low altitude aircraft, the MASTER has been operational since early 1998.

Instrument Type: Multispectral Imager
Measurements: VNIR/SWIR/MWIR/LWIR Imagery

The Multiple-Angle Aerosol Spectrometer Probe (MASP) determines the size and concentration of particles from about 0.3 to 20 microns in diameter and the index of refraction for selected sizes. Size is determined by measuring the light intensity scattered by individual particles as they transit a laser beam of 0.780µm wavelength. Light scattered from particles into a cone from 30 to 60 degrees forward and 120 to 150 degrees backwards is reflected by a mangin mirror through a condensing lens to the detectors. A comparison of the signals from the open aperture detector and the masked aperture detector is used to accept only those particles passing through the center of the laser beam. The size of the particle is determined from the total scattered light. The index of refraction of particles can be estimated from the ratio of the forward to back scatter signals. A calibration diode laser is pulsed periodically during flight to ensure proper operation of the electronics. The shrouded inlet minimizes angle of attack effects and maintains isokinetic flow through the sensing volume so that volatilization of particles is eliminated.