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NASA NTRS2015

Spectrographic Polarimeter and Method of Recording State of Polarity

A single-shot real-time spectropolarimeter for use in astronomy and other sciences that captures and encodes some or all of the Stokes polarization parameters simultaneously using only static, robust optical components with no moving parts is described. The polarization information is encoded onto the spectrograph at each wavelength along the spatial dimension of the 2D output data array. The varying embodiments of the concept include both a two-Stokes implementation (in which any two of the three Stokes polarization parameters are measured) and a full Stokes implementation (in which all three of the Stokes polarization parameters are measured), each of which is provided in either single beam or dual beam forms.

Sparks, William B.↗

NASA NTRS2014

High-Resolution Spectroscopy of the Lunar Sodium Exosphere

We have applied high-resolution Fabry-Perot spectroscopy to the study of the lunar sodium exosphere for the study of exospheric effective temperature and velocity variations. Observing from the National Solar Observatory McMath-Pierce Telescope, we used a dual-etalon Fabry-Perot spectrometer with a resolving power of 180,000 to measure line widths and Doppler shifts of the sodium D2 (5889.95 Å) emission line. Our field of view was 360 km, and measurements were made in equatorial and polar regions from 500 km to 3500 km off the limb. Data were obtained from full moon to 3 days following full moon (waning phase) in March 2009. Measured Doppler line widths within 1100 km of the sunlit east and south lunar limbs for observations between 5 and 40 deg lunar phase imply effective temperatures ranging between 3260 +/- 190 and 1000 +/- 135 K. Preliminary line center analysis indicates velocity displacements between different locations off the lunar limb ranging between 100 and 600 m/s from the lunar rest velocity with a precision of +/-20 to +/-50 m/s depending on brightness. Based on the success of these exploratory observations, an extensive program has been initiated that is expected to constrain lunar atmospheric and surface-process modeling and help quantify source and escape mechanisms.

Lunar↗

NASA NTRS2016

Advanced Antenna Design for NASA's EcoSAR Instrument

Advanced antenna arrays were designed for NASA's EcoSAR airborne radar instrument. EcoSAR is a beamforming synthetic aperture radar instrument designed to make polarimetric and "single pass" interferometric measurements of Earth surface parameters. EcoSAR's operational requirements of a 435MHz center frequency with up to 200MHz bandwidth, dual polarization, high cross-polarization isolation (> 30 dB), +/- 45deg beam scan range and antenna form-factor constraints imposed stringent requirements on the antenna design. The EcoSAR project successfully developed, characterized, and tested two array antennas in an anechoic chamber. EcoSAR's first airborne campaign conducted in the spring of 2014 generated rich data sets of scientific and engineering value, demonstrating the successful operation of the antennas.

phased array↗

NASA NTRS1989

Lightning trends as a precursor to microbursts

The feasibility of using lightning-rate data to aid in the early warning of microburst occurrence in moist environments is illustrated. Convective tendency images were generated for a small microburst-producing storm that developed in northern Alabama on July 20, 1986 during the Cooperative Huntsville Meteorological Experiment. Radar observations were obtained from the NCAR CP2 10-cm dual-polarization Doppler radar, while the measurements of total lightning activity were provided by the National Severe Storm Laboratory, a mobile laboratory that was located under the storm throughout its lifetime. The scenario for the evolution of wet microburst producing thunderstorms is described.

Buechler, Dennis E.↗

NASA NTRS1987

Imaging Radar Polarimeter

Radar measures full polarization tensor of each element in scene in one sweep. New system comprises dual-polarized antenna, single transmitter, and four-channel receiver and digital recorder installed in aircraft, plus digital processor on ground. Produces radar-backscatter images corresponding to 10- by 10-km regions on ground. Signals recorded from orthogonal linearly polarized antennas combined in computer after flight to synthesize any desired combination of transmitted and received polarizations. Data recorded on single flight processed to provide multiple images.

Zebker, Howard A.↗

NASA NTRS1985

Dual polarization VLBI observations of stellar binary systems at 5 GHz

The binary systems Sigma CrB, SZ Psc, HR 1099, UX Ari, HR 5110, Algol, and Cyg X-1 are characterized in terms of marcsec-scale radio structure on the basis of dual-polarization observations at 4.969-4.997 GHz, obtained with an international VLBI array comprising the 100-m Effelsberg, 36-m Haystack, 42-m Green Bank, 26-m Fort Davis, 130-m-equivalent VLA, and 40-m Owens Valley telescopes (system temperatures 40-70 K) at 22-14 h UT on July 26-27, 1983. The data are presented in graphs and tables and discussed in detail. Single Gaussian brightness distributions with theta(FWHM) = 0.5-2.0 marcsec and brightness temperatures (2-200) x 10 to the 8th K are determined for four sources; core-halo structures are found for UX Ari and Algol; and an upper limit of 50 microarcsec is established for the angular separation of the regions of left and right circular polarization. The gross features seen in RS CVn systems are explained in terms of a simple expanding-coronal-loop model of flare events.

Mutel, R. L.↗

NASA NTRS2016

Single-Event Latchup Testing of the Micrel MIC4424 Dual Power MOSFET Driver

We conducted 47 exposures of four different MIC4424 devices and did not observe any SEL or high-current events. This included worst-case conditions with a LET of 81 MeV-sq cm/mg, applied voltage of 18.5 V, a case temperature greater than 120 C, and a final fluence of 1x10(exp 7)/sq cm. We also monitored both the outputs for the presence of SETs. While the period of the 1 MHz square wave was slightly altered in some cases, no pulses were added or deleted. 1. Purpose: The purpose of this testing is to characterize the BiCMOS/DMOS Micrel MIC4424 dual, non-inverting MOSFET driver for single-event latchup (SEL) susceptibility. These data will be used for flight lot evaluation purposes. 2. Devices Tested: The MIC4423/4424/4425 family are highly reliable BiCMOS/DMOS buffer/driver MOSFET drivers. They are higher output current versions of the MIC4426/4427/4428. They can survive up to 5V of noise spiking, of either polarity, on the ground pin. They can accept, without either damage or logic upset, up to half an amp of reverse current (either polarity) forced back into their outputs. Primarily intended for driving power MOSFETs, the MIC4423/4424/4425 drivers are suitable for driving other loads (capacitive, resistive, or inductive) which require low-impedance, high peak currents, and fast switching times. Heavily loaded clock lines, coaxial cables, or piezoelectric transducers are some examples. The only known limitation on loading is that total power dissipated in the driver must be kept within the maximum power dissipation limits of the package. Five (5) parts were provided for SEL testing. We prepared four parts for irradiation and reserved one piece as an un-irradiated control. More information about the devices can be found in Table 1. The parts were prepared for testing by removing the lid from the CDIP package to expose the target die. The parts were then soldered to small copper circuit adapter boards for easy handling. These parts are fabricated in a bulk BiCMOS/DMOS technology. Since we do not know the number of overlayers used in the fabrication processes, linear energy transfer calculations are determined based on the top-surface incident ion species and kinetic energy.

Power MOSFET↗

NASA NTRS1973

Parabolic cylinder antennas

Some of the features of single and dual parabolic-cylinder reflector antenna systems are discussed in terms of wave conversions, field divergence, and wavefronts in Fresnel and Fraunhofer regions. Beam-squinting, by mechanical displacement and electrical phase gradient methods, is introduced together with the combination of these methods. In the case of dual parabolic cylinders there is also a discussion of surface-truncation, parametric representation of surface intersections, main-aperture blockage by the subsystem, and beam squinting. A few diffraction patterns are presented to illustrate the type of data available via a formulation equivalent to the complex-vector Kirchhoff-Kottler formulation. Main and cross-polarization components of the solution are available as they are inherently part of the field solution in the Cartesian coordinate system. A means of displaying main and cross-polarization components for arbitrary beam-scanning in space is outlined. Extensions to monopulse tracking with variable-beamwidth (zooming) capability are introduced.

Schmidt, R. F.↗

NASA NTRS1983

Differential reflectivity (Z-DR) measurements of rainfall compared with ground-based disdrometer measurements

The dual-polarization differential-reflectivity (Z-DR) radar technique of Seliga and Bringi (1976) is used to determine rainfall rates and drop sizes over a site located at a distance of 47.1 km, and the results are analyzed using the empirical calibration relations of Seliga et al. (1983) and compared with electromechanical-disdrometer measurements. The data are presented in graphs and found to be well correlated, demonstrating the validity of the Z-DR estimates and the improvement introduced by applying the empirical relations rather than an a priori drop-size distribution.

Direskeneli, H.↗

NASA NTRS1975

Soil moisture detection from radar imagery of the Phoenix, Arizona test site

The Environmental Research Institute of Michigan (ERIM) dual-polarization X and L band radar was flown to acquire radar imagery over the Phoenix (Arizona) test site. The site was covered by a north-south pass and an east-west pass. Radar response to soil moisture was investigated. Since the ERIM radar does not have accurately measured antenna patterns, analysis of the L band data was performed separately for each of several strips along the flight line, each corresponding to a narrow angle of incidence. For the NS pass, good correlation between the radar return and mositure content was observed for each of the two nearest (to nadir) angular ranges. At higher angular ranges, no correlation was observed. The above procedure was not applied to the EW pass due to flight path misalignments. The results obtained stress the importance of radar calibration, the digitization process, and the angle of incidence.

Cihlar, J.↗

NASA NTRS2001

Duplex Direct Data Distribution System

The NASA Glenn Research Center (GRC) is developing and demonstrating communications and network technologies that are helping to enable the near-Earth space Internet. GRC envisions several service categories. The first of these categories is direct data distribution or D3 (pronounced "D-cubed"). Commercially provided D3 will make it possible to download a data set from a spacecraft, like the International Space Station. as easily as one can extract a file from a remote server today, using a file transfer protocol. In a second category, NASA spacecraft will make use of commercial satellite communication (SATCOM) systems. Some of those services will come from purchasing time on unused transponders that cover landmasses. While it is likely there will be gaps in service coverage, Internet services should be available using these systems. This report addresses alternative methods of implementing a full duplex enhancement of the GRC developed experimental Ka-Band Direct Data Distribution (D3) space-to-ground communication link. The resulting duplex version is called the Duplex Direct Data Distribution (D4) system. The D4 system is intended to provide high-data-rate commercial direct or internet-based communications service between the NASA spacecraft in low earth orbit (LEO) and the respective principal investigators associated with these spacecraft. Candidate commercial services were assessed regarding their near-term potential to meet NASA requirements. Candidates included Ka-band and V-band geostationary orbit and non-geostationary orbit satellite relay services and direct downlink ("LEO teleport") services. End-to-end systems concepts were examined and characterized in terms of alternative link layer architectures. Alternatives included a Direct Link, a Relay Link, a Hybrid Link, and a Dual Mode Link. The direct link assessment examined sample ground terminal placements and antenna angle issues. The SATCOM-based alternatives examined existing or proposed commercial SATCOM services that could be available in the 2005 time frame. The alternatives were evaluated and compared in terms of average daily system throughput and cost per bit. Throughput was estimated based on hypothetical scenarios supporting the International Space Station and polar orbiting missions. The feasibility of using standard TCP and a modified TCP was evaluated and risks were identified. An estimate of the TCP acknowledgment data rate required to support a return channel rate of 622 Mbps was developed using OPNET.

Greenfield, Israel↗

NASA NTRS2005

Recent Advances in Radar Polarimetry and Polarimetric SAR Interferometry

The development of Radar Polarimetry and Radar Interferometry is advancing rapidly, and these novel radar technologies are revamping Synthetic Aperture Radar Imaging decisively. In this exposition the successive advancements are sketched; beginning with the fundamental formulations and high-lighting the salient points of these diverse remote sensing techniques. Whereas with radar polarimetry the textural fine-structure, target-orientation and shape, symmetries and material constituents can be recovered with considerable improvements above that of standard amplitude-only Polarization Radar ; with radar interferometry the spatial (in depth) structure can be explored. In Polarimetric-Interferometric Synthetic Aperture Radar (POL-IN-SAR) Imaging it is possible to recover such co-registered textural plus spatial properties simultaneously. This includes the extraction of Digital Elevation Maps (DEM) from either fully Polarimetric (scattering matrix) or Interferometric (dual antenna) SAR image data takes with the additional benefit of obtaining co-registered three-dimensional POL-IN-DEM information. Extra-Wide-Band POL-IN-SAR Imaging - when applied to Repeat-Pass Image Overlay Interferometry - provides differential background validation and measurement, stress assessment, and environmental stress-change monitoring capabilities with hitherto unattained accuracy, which are essential tools for improved global biomass estimation. More recently, by applying multiple parallel repeat-pass EWB-POL-D(RP)-IN-SAR imaging along stacked (altitudinal) or displaced (horizontal) flight-lines will result in Tomographic (Multi- Interferometric) Polarimetric SAR Stereo-Imaging , including foliage and ground penetrating capabilities. It is shown that the accelerated advancement of these modern EWB-POL-D(RP)-IN-SAR imaging techniques is of direct relevance and of paramount priority to wide-area dynamic homeland security surveillance and local-to-global environmental ground-truth measurement and validation, stress assessment, and stress-change monitoring of the terrestrial and planetary covers. In addition, various closely related topics of (i) acquiring additional and protecting existing spectral windows of the Natural Electromagnetic Spectrum (NES) pertinent to Remote Sensing; (ii) mitigating against common "Radio Frequency Interference (RFI)" and intentional Directive Jamming of Airborne & Space borne POL-IN-SAR Imaging Platforms are appraised.

Boerner, Wolfgang-Martin↗

NASA NTRS1998

On the Predictability of Substorms Following Sharp Northward Turnings of the IMF

It has been shown that there is an association between changes of the interplanetary magnetic field (IMF) that are expected to lead to a reduction in magnetospheric convection (northward turnings, reductions) and the onset of the expansion phase of substorms. This has been previously demonstrated by analyses of IMF data during time intervals associated with identified substorm onsets. Here we examine whether observations of northward turnings of the IMF can be used to predict the occurrence of substorms. We first identified sharp northward turnings that follow an interval of steady, southward IMF using measurements from the Wind spacecraft during the first 180 days of 1997. We also required that the northward turning be observed by either IMP-8 or GEOTAIL, in addition to Wind, and that one of the observing satellites be sufficiently close to the Earth-Sun line, or that the two observing satellites be sufficiently separated, that we are reasonably certain that the northward turning affected the magnetosphere. We also used the dual observations to estimate the arrival of the northward turning at the Earth. Using these criteria, we predicted 17 substorms. We then searched for the following signatures of substorm onset around the time of the predicted onset: auroral brightening followed by auroral bulge expansion observed by Polar UVI, geosynchronous particle injection, geosynchronous magnetic field dipolarization, and an appropriate magnetic disturbance at the surface of the Earth. Of the 17 predictions of substorms, 10 were successful in that a substorm onset was observed within 12 min of the predicted onset, 1 is indeterminate due to a lack of data at the Earth, 1 had unusual activity that we have not been able to identify, and 5 were unsuccessful. The failure of these last 5 predictions is explicable. Two of the northward turnings that failed to produce substorms were preceded by the lowest average of the set. The remaining 3 were the only cases in which the northward turning was accompanied by a simultaneous sharp increase. The increase would be expected to offset the decrease in convection that would otherwise be expected to be associated with a northward turning. These results indicate that it is an IMF change that leads to a reduction in convection, rather than just a northward turning or reduction that is associated with substorms, and that at least some substorms can be predicted by measurements of the IMF.

Blanchard, G. T.↗

NASA NTRS1993

Airborne full polarization radiometry using the MSFC Advanced Microwave Precipitation Radiometer (AMPR)

The applications of vertically and horizontally polarized brightness temperatures in both atmospheric and surface remote sensing have been long recognized by many investigators, particularly those studying SMMR and SSM/I data. Here, the large contrast between the first two Stokes' parameters (T(sub V) and T(sub H)) can be used for detection of sea ice, measurement of ocean surface wind speed, and measurement of cloud and water vapor opacity. High-resolution aircraft data from instruments such as the NASA/MSFC AMPR is crucial for verifying radiative transfer models and developing retrieval algorithms. Currently, the AMPR is outfitted with single-polarization channels at 10, 18, 37 and 85 GHz. To increase its utility, it is proposed that additional orthogonal linearly polarized channels be added to the AMPR. Since the AMPR's feedhorns are already configured for dual orthogonal linearly polarized modes, this would require only a duplication of the currently existing receivers. To circumvent the resulting polarization basis skew caused by the cross-track scanning mechanism, the technique of Electronic Polarization Basis Rotation is proposed to be implemented. Implementation of EPBR requires precise measurement of the third Stokes parameter and will eliminate polarization skew by allowing the feedhorn basis skew angle to be corrected in software. In addition to upgrading AMPR to dual polarization capability (without skew), the modifications will provide an opportunity to demonstrate EPBR on an airborne platform. This is a highly desirable intermediate step prior to satellite implementation.

Gasiewski, Al J.↗

NASA NTRS1979

A decision-directed network for dual-polarization crosstalk cancellation

Frequency reuse in the specific form of dual-polarized microwave communication systems has grown in importance in recent years as a practical means of radio spectrum conservation. Ideally the capacity of a given frequency allocation can be doubled through dual-polarization. However, hardware imperfections and propagation effects, particularly rain depolarization, prevent the achievement of this doubling without severe system performance degradation. A decision-directed cross-polarization correction network is presented whose operation depends on only simple base-band signal processing. No pilot tones or frequency offsets are required. The loop can work with any two-dimensional signal set for digital data transmission. The loop has been experimentally verified and provides a means of doubling the data capacity with little performance degradation.

Weber, W. J., III↗

NASA NTRS1987

Retrieval of surface roughness parameters from dual-frequency measurements of radar backscattering coefficients

The use of dual-frequency data of backscattering coefficients at a fixed angle to estimate surface roughness parameters is evaluated. Radar backscattering coefficients at 1.5 and 4.25 GHz are calculated using a model based on Kirchhoff approximation of electromagnetic wave scatttering from a rough soil surface. Plots of the calculated backscattering coefficients for Kansas soil moisture contents at the C- and L-band frequencies and HH polarization are analyzed. The effects of changes in correlation length on the backscattering coefficients are investigated. The calculated backscattering coefficients are compared with scatterometer data collected at 1.5 and 4.25 GHz, and it is detected that the model and field data correlate well. The data reveal that it is possible to retrieve the surface roughness parameters from measured radar data.

Mo, Tsan↗

NASA NTRS2000

Low-Cost Tracking Ground Terminal Designed to Use Cryogenically Cooled Electronics

A computer-controlled, tracking ground terminal will be assembled at the NASA Glenn Research Center at Lewis Field to receive signals transmitted by the Glenn's Direct Data Distribution (D3) payload planned for a shuttle flight in low Earth orbit. The terminal will enable direct data reception of up to two 622-megabits-per-second (Mbps) beams from the space-based, K-band (19.05-GHz) transmitting array at an end-user bit error rate of up to 10(exp -12). The ground terminal will include a 0.9-m-diameter receive-only Cassegrain reflector antenna with a corrugated feed horn incorporating a dual circularly polarized, K-band feed assembly mounted on a multiaxis, gimbaled tracking pedestal as well as electronics to receive the downlink signals. The tracking system will acquire and automatically track the shuttle through the sky for all elevations greater than 20 above the horizon. The receiving electronics for the ground terminal consist of a six-pole microstrip bandpass filter, a three-stage monolithic microwave integrated circuit (MMIC) amplifier, and a Stirling cycle cryocooler (1 W at 80 K). The Sterling cycle cryocooler cools the front end of the receiver, also known as the low-noise amplifier (LNA), to about 77 K. Cryocooling the LNA significantly increases receiver performance, which is necessary so that it can use the antenna, which has an aperture of only 0.9 m. The following drawing illustrates the cryoterminal.

Wald, Lawrence W.↗

NASA NTRS1980

Whistler mode wave packets in the earth's foreshock region

Measurements of the velocity of discrete whistler-mode wave packets in the region upstream of the earth's bow shock are presented. Data from the dual magnetometers aboard the ISEE 1 and 2 spacecraft was used to determine the time delay between the appearance of a wavefront at each spacecraft in order to obtain the wave velocity in the spacecraft frame, and from it the intrinsic wave phase velocity. Results from the 11 events characterized by sufficiently large velocities reveal the wave packets to exhibit a nearly perfectly circular polarization with the packet field rotating in the left-hand sense about the ambient field direction in the spacecraft frame. In the plasma rest frame, these waves are found to be right-handed polarized waves with frequencies several times the proton gyrofrequency which are attempting to propagate upstream against the solar wind but are in fact being carried towards the earth by the solar wind flow.

Hoppe, M.↗