Synonyms: 
DC8
DC-8
NASA DC8
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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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Polarimetric Ku-Band Scatterometer

PolSCAT is a Ku-band polarmetric scanning scatterometer operating at 13.95 GHz. with an approved NASA license. The transmitting polarizations of PolSCAT, alternating between Vertical and Horizontal, from pulse to pulse. Two receivers detect the V and H polarized radar echoes simultaneously allowing for measurements of VV, HH, VH, and HV radar responses. It provides scalable resolution, between 3,000 and 20,000 feet AGL.

The PolSCAT antenna assembly includes two axis gimbals for conically scanning, parabolic antenna, which is controlled from 0° (nadir) to 65 degrees. It was designed and built to investigate the benefits of active microwave for the remote sensing of high resolution snow-water-equivalent (SWE).

PolSCAT’s flexible design is compatible with many aircraft. It has flown on the NCAR C-130, NASA’s DC-8, P-3, and Twin Otter International’s, Twin Otter. Flown more than 500 hours in support of NASA’s Cold Land Process (CLPX) campaigns, PolSCAT is a very mature instrument.

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Passive Active L- and S-band Sensor

PALS is a combined polarimetric radiometer and NASA licensed radar sharing a rotating planar array antenna. The PALS instrument includes a combined L-band radiometer and scatterometer , operating at 1.413 GHz and 1.26 GHz respectively. It was designed and built to investigate the benefits of combining passive and active microwave sensors for Ocean salinity and Soil moisture remote sensing. It is the prototype for the Aquarius and SMAP missions and its flexible design is compatible with many aircraft.

The PALS radar and radiometer time share a dual pole, dual frequency planner array antenna. The antenna configuration can be fixed or rotating. It provides scalable resolution, between 3,000 and 20,000 feet AGL. It is an Aquarius and SMAP test bed.

PALS has flown on the NCAR C-130, NASA’s P-3 and Twin Otter International’s, Twin Otter. It is a very mature instrument, and has flown more than 800 hours, in support of NASA campaigns.

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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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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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Polarimetric Scanning Radiometer - Original Scanhead

The PSR/A scanhead provides either full-Stokes vector or tri-polarimetric sensitivity at the radiometric bands of 10.7, 18.7, and 37 GHz, and thus is well suited for the NPOESS Integrated Program Office’s internal government (IG) studies of ocean surface wind vector measurements. PSR data has been used to demonstrate the first-ever retrieval of ocean surface wind fields using conically-scanned polarimetric radiometer data. The results have suggested that the NPOESS specification for wind vector accuracy will be achievable with a polarimetric two-look system.

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Polarimetric Scanning Radiometer

The Polarimetric Scanning Radiometer (PSR) is a versatile airborne microwave imaging radiometer developed by the Georgia Institute of Technology and the NOAA Environmental Technology Laboratory (now NOAA/ESRL PSD) for the purpose of obtaining polarimetric microwave emission imagery of the Earth's oceans, land, ice, clouds, and precipitation. The PSR is the first airborne scanned polarimetric imaging radiometer suitable for post-launch satellite calibration and validation of a variety of future spaceborne passive microwave sensors. The capabilities of the PSR for airborne simulation are continuously being expanded through the development of new mission-specific scanheads to provide airborne post-launch simulation of a variety of existing and future U.S. sensors, including CMIS, ATMS, AMSU, SSMIS, WindSat, TMI, RAMEX, and GEM.

The basic concept of the PSR is a set of polarimetrc radiometers housed within a gimbal-mounted scanhead drum. The scanhead drum is rotatable by the gimbal positioner so that the radiometers (Figure 2.) can view any angle within ~70° elevation of nadir at any azimuthal angle (a total of 1.32 pi sr solid angle), as well as external hot and ambient calibration targets. The configuration thus supports conical, cross-track, along-track, fixed-angle stare, and spotlight scan modes. The PSR was designed to provide several specific and unique observational capabilities from various aircraft platforms. The original design was based upon several observational objectives:

1. To provide fully polarimetric (four Stokes' parameters: Tv, Th, TU, and TV) imagery of upwelling thermal emissions at several of the most important microwave sensing frequencies (10.7, 18.7, 37.0, and 89.0 GHz), thus providing measurements from X to W band;
2. To provide the above measurements with absolute accuracy for all four Stokes' parameters of better than 1 K for Tv and Th, and 0.1 K for TU and TV;
3. To provide radiometric imaging with both fore and aft look capability (rather than single swath observations);
4. To provide conical, cross-track, along-track, and spotlight mode scanning capabilities; and
5. To provide imaging resolutions appropriate for high resolution studies of precipitating and non-precipitating clouds, mesoscale ocean surface features, and satellite calibration/validation at Nyquist spatial sampling.

The original system has been extended - as discussed below - to greatly exceed the original design objectives by providing additional radiometric channels and expanded platform capabilities.

The PSR scanhead was designed for in-flight operation without the need for a radome (i.e., in direct contact with the aircraft slipstream), thus allowing precise calibration and imaging with no superimposed radome emission signatures. Moreover, the conical scan mode allows the entire modified Stokes' vector to be observed without polarization mixing.

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Applanix POS System

POS AV is a hardware and software system specifically designed for direct georeferencing of airborne sensor data. By integrating precision GNSS with inertial technology, POS AV enables geospatial projects to be completed more efficiently, effectively, and economically. POS AV is engineered for aerial cameras, scanning lasers, imaging sensors, synthetic aperture radar, and LIDAR technology.

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