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WB-57
WB57
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Nevzorov Liquid Water Content (LWC) and Total Water Content (TWC) Probe

The Nevzorov liquid water content (LWC) and total water content (TWC) probe is a constant-temperature, hot-wire probe designed for aircraft measurements of the ice and liquid water content of clouds. The probe consists of two separate sensors for measurements of cloud liquid and total (ice plus liquid) water content. Each sensor consists of a collector and a reference winding. The reference sensors are shielded from impact with cloud particles, specifically to provide an automatic compensation for convective heat losses.

The sensitivity of the probe is estimated to be approximately 0.003– 0.005 g m23. The accuracy of LWC measurements in nonprecipitating liquid clouds is estimated as 10%–15%. Tests at the NRC high-speed icing tunnel have provided verification of the TWC measurement for small frozen droplets to an accuracy of approximately 10%–20%, but verification in snow and natural ice crystals has not yet been possible due to the absence of any accurate standards. The TWC measurement offers not only the possibility of direct measurements of ice content but also improved liquid water contents in drizzle situations. Airborne measurements have provided data on the baseline drift and sensitivity of the probe and have provided comparisons to other conventional instruments. Several cases have been documented that exhibit the unique capabilities of the instrument to separate the ice and liquid components of supercooled clouds.

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PAN and Trace Hydrohalocarbon ExpeRiment

PANTHER uses Electron Capture Detection and Gas Chromatography (ECD-GC) and Mass Selective Detection and Gas Chromatography (MSD-GC) to measure numerous trace gases, including Methyl halides, HCFCs, PAN, N20, SF6, CFC-12, CFC-11, Halon-1211, methyl chloroform, carbon tetrachloride.

3 ECD (electron capture detectors), packed columns (OV-101, Porpak-Q, molecular sieve).

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

2-channel MSD (mass selective detector). The MSD analyses two independent samples concentrated onto TE cooled Haysep traps, then passed 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 is 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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Scanning High-Resolution Interferometer Sounder

The Scanning High-resolution Interferometer Sounder (S-HIS) is a scanning interferometer which measures emitted thermal radiation at high spectral resolution between 3.3 and 18 microns The measured emitted radiance is used to obtain temperature and water vapor profiles of the Earth's atmosphere in clear-sky conditions. S-HIS produces sounding data with 2 kilometer resolution (at nadir) across a 40 kilometer ground swath from a nominal altitude of 20 kilometers onboard a NASA ER-2 or Global Hawk.

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Scanning Actinic Flux Spectroradiometers

The SAFS instruments determine wavelength dependent actinic flux from 280-420 nm. The actinic flux in combination with the absorption cross section and quantum yield molecular data will be used to calculate the photolysis frequencies of multiple photochemically important molecular processes, including O3, NO2, HONO, CH2O, H2O2, CH3OOH, HNO3, PAN, CH3NO3, CH3CH2NO3, and CH3COCH3.

The SAFS measurement is based on a 2p steradian hemisphere hemispherical quartz light collector, a double monochromator, and a low dark current photomultiplier. The monochromator employs dual 2400 G/mm gratings which produce a 1 nm FWHM spectral resolution and very low straylight. The instrument package on the aircraft includes two independent, but time synchronized (IRIG-B) spectroradiometer systems to measure the up- and down-welling fluxes in a 10 second scan time. Summing these produces the spherically integrated actinic flux.

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Research Environment for Vehicle-Embedded Analysis on Linux

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RC-10 Mapping Cameras

Wild Heerbrugg RC-10 Mapping Cameras with a 9 x 9 inch image format are flown on virtually every ER-2 earth imaging mission. The RC-10s may be employed with six or twelve inch focal length lenses providing image scales of two miles to the inch and one mile to the inch respectively. RC-10 mounting stations include the ER-2 Q-bay, nose pod and the right and left wing pods.

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Polarimetric Scanning Radiometer - C/X Band

Remote sensing of soil moisture using C- and X-band microwave frequencies provides less penetration of vegetation and soil probing depth than L-band, but is more amenable to implementation using airborne or spaceborne antennas of practical size. The Japanese AMSR-E imaging radiometer on board the NASA EOS Aqua satellite is one such sensor capable of retrieving soil moisture using a microwave channel at 6.9 GHz with ~75 km spatial resolution. Aqua was launched in May 2002, and will provide a global soil moisture product based on AMSR-E data. The C-band channels on the future NPOESS Conical Microwave Imager and Sounder (CMIS) will provide new operational capabilities for mapping soil moisture. Sea surface temperature is also observable under most cloud conditions using passive microwave C-band radiometry.

To provide airborne mapping capabilities for measuring both soil moisture and sea surface temperature a second operational PSR scanhead was built incorporating fully polarimetric C- and X-band radiometers inside a standard PSR scanhead drum. The C-band radiometer in PSR/CX provides vertically and horizontally polarized measurements within four adjacent subbands at 5.80-6.20, 6.30-6.70, 6.75-7.10, and 7.15-7.50 GHz. In addition, the radiometer provides fully polarimetric measurements at 6.75-7.10 GHz. The use of four subbands and polarimetric capability has provided a unique means of demonstrating and optimizing algorithms for RFI mitigation.

PSR/CX was originally implemented using only a C-band radiometer (as PSR/C) in preparation for SGP99. In preparation for SMEX02 an X-band radiometer was added to provide vertically and horizontally polarized measurements within four bands at 10.60-10.68, 10.68-10.70, 10.70-10.80, and 10.60-10.80 GHz. Fully polarimetric measurements are provided within 10.60-10.80 GHz. The combined dual-band system provides additional information on soil moisture, along with the capability to measure precipitation and the near-surface wind vector over water backgrounds. The X-band channels also provide additional RFI mitigation capability.

Applications of PSR/CX include ocean surface emissivity studies, soil moisture mapping, sea ice mapping, and imaging of heavy precipitation.

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