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Results for “RADAR REFLECTOR”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Demonstration of radar reflector detection and ground clutter suppression using airborne weather and mapping radar

A navigation system which utilizes minimum ground-based equipment is especially advantageous to helicopters, which can make off-airport landings. Research has been conducted in the use of weather and mapping radar to detect large radar reflectors overland for navigation purposes. As initial studies have not been successful, investigations were conducted regarding a new concept for the detection of ground-based radar reflectors and eliminating ground clutter, using a device called an echo processor (EP). A description is presented of the problems associated with detecting radar reflectors overland, taking into account the EP concept and the results of ground- and flight-test investigations. The echo processor concept was successfully demonstrated in detecting radar reflectors overland in a high-clutter environment. A radar reflector target size of 55 dBsm was found to be adequate for detection in an urban environment.

Anderson, D. J.↗
NASA NTRS1965

Inflatable radar reflector unit Patent

Inflatable radar reflector unit - lightweight, highly reflective to electromagnetic radiation, and adaptable for erection and deployment with minimum effort and time

Radnofsky, M. I.↗
NASA NTRS1993

On the estimation of the correlation dimension and its application to radar reflector discrimination

Recently, system theorists have recognized that low order systems of nonlinear differential equations can give rise to solutions which are neither periodic, constant, nor predictable in steady state, but which are nonetheless bounded and deterministic. This behavior, which was first described in the study of weather systems, has been termed 'chaotic.' Much study of chaotic systems has concentrated on analysis of the systems' phase space attractors. It has been recognized that invariant measures of the attractor possess inherent information about the system. One such measure is the dimension of the attractors. The dimension of a chaotic attractor has been shown to be noninteger, leading to the term 'strange attractor;' the attractor is said to have a fractal structure. The correlation dimension has become one of the most popular measures of dimension. However, many problems have been identified in correlation dimension estimation from time sequences. The most common methods for obtaining the correlation dimension have been least squares curves fitting to find the slope of the correlation integral and the Takens Estimator. However, these estimates show unacceptable sensitivity to the upper limit on the distance chosen. Here, a new method is proposed which is shown to be rather insensitive to the upper limit and to perform in a very stable manner, at least in the absence of noise. The correlation dimension is also shown to be an effective discriminant in distinguishing between radar returns resulting from weather and those from the ground. The weather returns are shown to have a correlation dimension generally between 2.0 and 3.0, while ground returns have a correlation dimension exceeding 3.0.

Barnett, Kevin D.↗
NASA NTRS1990

Cheap Corner Reflectors For Radar

Corner reflectors for radar constructed easily and inexpensively. Wire mesh on plastic pipe forms retroreflective panels of triangular or square shape. Panels joined by bolts and wingnuts. Overlapping panel edges ensure mutual perpendicularity. Materials for new reflectors found in hardware and building-supply stores. No special skills or tools needed for assembly.

Caro, E. R.↗
NASA NTRS1987

Radar polarimeter measures orientation of calibration corner reflectors

Radar polarimeter signals from a set of trihedral corner reflectors located in the Goldstone Dry Lake in California were analyzed, and three types of scattering behavior were observed: (1) Bragg-like slightly rough surface scattering that represents the background signal from the dry lake, (2) trihedral corner reflector scattering that returns the incident polarization, and (3) two-bounce corner reflector scattering resulting from a particular alignment of a trihedral reflector. A radar calibration approach using trihedral corner reflectors should be designed such that precise alignment of the reflectors is ensured, as three-bounce and two-bounce geometries lead to very different cross sections and hence very different inferred calibration factors.

Zebker, Howard A.↗
NASA NTRS1989

A chamber experiment for the feasibility study of an artificial plasma reflector for OTH radar applications

The feasibility of using two intersecting beams for plasma generation in the upper atmosphere as an over-the-horizon radar reflector was investigated. A cube was filled with dry air to a pressure corresponding to the simulated altitude, and two components of a split microwave beam were fed into the cube at right angles. Plasma layers were generated where the two beams intersected. Three critical issues were addressed: (1) reflectivity of the generated plasma layers; (2) propagation of high power microwave pulses; and (3) lifetime of the plasma.

Kuo, S. P.↗
NASA NTRS1984

Radar-visible wind streaks in the Altiplano of Bolivia

Isolated knobs that are erosional remnants of central volcanoes or of folded rocks occur in several areas of the Altiplano are visible on both optical and images. The optically visible streaks occur in the immediate lee of the knobs, whereas the radar visible streaks occur in the zone downwind between the knobs. Aerial reconnaissance and field studies showed that the optically visible streaks consist of a series of small ( 100 m wide) barchan and barchanoid dunes, intradune sand sheets, and sand hummocks (large shrub coppice dunes) up to 15 m across and 5 m high. On LANDSAT images these features are poorly resolved but combine to form a bright streak. On the radar image, this area also appears brighter than the zone of the radar dark streak; evidently, the dunes and hummocks serve as radar reflectors. The radar dark streak consists of a relatively flat, smooth sand sheet which lacks organized aerolian bedforms, other than occasional ripples. Wind velocity profiles show a greater U value in the optically bright streak zone than in the radar dark streak.

Greeley, R.↗
NASA NTRS2008

Development of the Aquarius Antenna Deployment Mechanisms and Spring/Damper Actuator

The Aquarius Instrument s large radar reflector dish needed to be stowed for launch, and then deployed on-orbit. The Deployment Subsystem consisted of a cantilevered boom structure and two single-axis hinge mechanisms to accurately deploy and position the reflector dish relative to the radar feed horns. The cantilevered design demanded high stiffness and accuracy from the deployment mechanism at the root of the boom. A preload-generating end-of-travel latch was also required. To largely eliminate the need for control systems, each deployment mechanism was actuated by a passive spring motor with viscous-fluid damping. Tough requirements and adaptation of a heritage actuator to the new application resulted in numerous challenges. Fabrication, assembly, and testing encountered additional problems, though ultimately the system was demonstrated very successfully. This paper revisits the development to highlight which design concepts worked and the many important lessons learned.

Johnson, Joel A.↗
NASA NTRS1986

SIR-B radar imagery of volcanic deposits in the Andes

Synthetic-aperture radar imagery from the Shuttle Imaging Radar - mission B (SIR-B) was collected in October 1984 over the central Andes between 20 deg S and 24 deg S and also south of 42 deg S. Despite signal-strength problems that drastically reduced the signal-to-noise ratio of the images, volcanic features of both areas show up well. In particular, ignimbrite sheets formed by large explosive eruptions stand out as very strong radar reflectors. High backscatter is apparently caused by erosional relief on the ignimbrites at scales ranging from the radar wavelength (23 cm for SIR-B) to the 30-200-m scale of quebradas (gullies and canyons). The consistent regional erosional pattern appears unrelated to the emplacement of the ignimbrites, and is probably caused by preferential eolian erosion in the directions of the prevailing wind. Hand-held space photographs, ground observations, and Landsat Thematic Mapper imagery support the interpretation of the ignimbrite radar signature. The Chilean volcano Michinmahuida was imaged by four radar data takes at different incidence angles, which show tectonic, glacial, and volcanic features of that nearly inaccessible and often cloud-covered region. Stereo viewing of radar images from two data takes greatly enhances the geologic interpretation of this rugged area.

Fielding, E. J.↗
NASA NTRS2003

Analysis of Near Simultaneous Jimsphere and AMPS High Resolution Wind Profiles

The high-resolution wind profile of the Automated Meteorological Profiling System (HRAMPS) is the proposed replacement for the Jimsphere measurement system used to support NASA Shuttle launches from the Eastern Test Range (ETR). Samples of twenty-six ETR near simultaneous Jimsphere and HRAMPS wind profiles were obtained for Shuttle program HRAMPS certification studies. Shuttle systems engineering certification is to ensure that spacecraft and launch vehicle systems performance and safety evaluations for each launch (derived from flight simulations with Jimsphere wind profile data bases) retain their validity when HRAMPS profiles are used on day-of-launch (DOL) in trajectory and loads simulations to support the commit-to-launch decision. This paper describes a statistical analysis of the near simultaneous profiles. In principle the differences between a Jimsphere profile and an HRAMPS profile should be attributed to tracking technology (radar versus GPS tracking of a Jimsphere flight element) and the method for derivation of wind vectors from the raw tracking data. In reality, it is not technically feasible to track the same Jimsphere balloon with the two systems. The aluminized Mylar surface of the standard Jimsphere flight element facilitates radar tracking, but it interferes with HRAMPS during simultaneous tracking. Suspending a radar reflector from an HRAMPS flight element (Jimsphere without aluminized coating) does not produce satisfactory Jimsphere profiles because of intermittent radar returns. Thus, differences between the Jimsphere and HRAMPS profiles are also attributed to differences in the trajectories of separate flight elements. Because of small sample size and a test period limited to one winter season, test measurements during extreme high winds aloft could not have been expected and did not occur. It is during the highest winds that the largest differences between Jimsphere and HRAMPS would occur because the distance between flight elements would be larger. Jimsphere radar tracking noise increases as a function of balloon displacement downrange. The Jimsphere data processing compensates for tracking signal/noise degradation by increasing the smoothing interval. The Jimsphere wind profile effective resolution is a function of downrange distance and altitude, whereas the effective resolution of the HRAMPS should be independent of those variables. The procedure used for editing Jimsphere spikes in Shuttle DOL profiles was not implemented for the Jimsphere profile measurements during the AMPS field tests. For this analysis a code was developed that essentially mimics DOL Jimsphere spike editing. Jimsphere profiles have somewhat more noise in the wavelength range less than 200m defined as the noise floor. No differences between Jimsphere and HRAMPS wind profile pairs have been found that would support denial of HRAMPS certification for application in Shuttle DOL applications. The reliability of the HRAMPS system, which is an important certification issue, is not addressed in this study.

Adelfang, S. I.↗
NASA NTRS1978

Orbital radar evidence for lunar subsurface layering in Maria Serenitatis and Crisium

Data from the lunar-orbiting Apollo 17 radar sounding experiment (60-m wavelength) have been examined in both digital and holographic formats, and it is concluded that there are two subsurface radar reflectors below the surface in Mare Serenitatis and one reflector below the surface in Mare Crisium. The mean apparent depths of the reflectors below the surface of the former Mare are 0.9 and 1.6 km, while the reflector below the surface of the latter Mare has a mean depth of 1.4 km. These reflectors represent basin-wide subsurface interfaces. Techniques for reducing surface backscatter (clutter) in the data are described, and reasons for thinking that the distinct alignments in radar returns represent subsurface reflecting horizons are explained

Peeples, W. J.↗
NASA NTRS1977

The rings of Saturn - Two-frequency radar observations

Results are reported for a two-frequency dual-polarization radar-echo study of Saturn's rings which involved monostatic operation at a wavelength of 3.5 cm and bistatic operation at 12.6 cm. The radar observations show that the rings effectively depolarize linearly and circularly polarized incident waves at the two wavelengths; that the ring particles are unusually efficient radar reflectors, yielding approximately the same high total cross section at both wavelengths; and that there is an apparent excess of power at the 'central' Doppler shifts when compared with homogeneous scattering models based on the optically observed ring distributions. Several possible explanations for these three radar properties are considered. It is found that a model which hypothesizes a thick cloud of irregular water-ice chunks a few centimeters or larger in radius and a model which postulates a monolayer of multimeter-sized water-frost-coated metallic chunks both seem capable of explaining the first two radar properties. But no consistent explanation is found for the excess low-frequency spectral power.

Goldstein, R. M.↗
NASA NTRS2000

Radar Reflectivity of the Martian Polar Regions

Radar experiments provide a unique method of probing the surfaces and subsurfaces of planetary bodies. Information on surface and subsurface structures and properties can be extracted from radar data. There is a well developed history of radar investigations of the planet Mars, beginning with the first reports of variations of scattering properties as a function of martian longitude in the mid-1960's. Because of the rapid rotation of Mars, the standard technique of delay-doppler mapping cannot be used as effectively as it is on Mercury and Venus, making it a more difficult radar target. Techniques have been developed to overcome this difficulty, including an inversion technique to combine many doppler-only (CW) experiments from different viewing geometries into a map of surface reflectivity, and new random long-code techniques. These techniques still suffer from ambiguities, however. A third technique which does not suffer from these ambiguities is the combination of the powerful Goldstone transmitter with the VLA as the receiving instrument to create a combined radar imaging instrument. We have used this combined radar instrument to image the surface of Mars in 3.5-cm radar reflectivity during the 1988, 1992/93, and 1999 oppositions. During the 1988 experiments, the residual south polar ice cap (RSPIC) was the brightest radar reflector on the planet - intrinsically brighter than even the Tharsis lava flows. This was quite an unexpected result. In contrast, during the 1992/93 experiments, the residual north polar ice cap (RNPIC) was not nearly so bright, and in fact showed no enhancement at all, This was puzzling, given the 1988 results for the RSPIC. We attributed the lack of a radar reflection enhancement to a combination of three effects: the geometry was different; the season was different; and the intrinsic scattering from the residual ice caps was different. The 1999 experiments provided a chance to test the relative importance of these three effects, since the RNPIC would be visible in a geometry very similar to the RSPIC in 1988, and the season would also be very similar. Preliminary reduction of the data taken in 1999 shows that the RNPIC did in fact show a radar reflectivity enhancement, but that it was still not as bright as the RSPIC in 1988. Details regarding the radar reflectivity of the residual ice caps, as well as the surrounding polar layered terrains (in light of our radar reflectivity data) will be discussed. Additional information is contained in the original extended abstract.

Butler, B. J.↗
NASA NTRS1978

Regional deformation of mare surfaces

The possible tectonic significance of large topographic irregularities within Mare Serenitatis is discussed, and the characteristics of sinuous rilles are considered as possible indicators of structural deformation. It is shown that most sinuous rilles have been structurally warped and that their slopes lie within the laminar flow range. The sinuous rilles may have been formed in the domain of turbulent flow, if the ratios of meander wavelength to channel width can be taken as indicators. Some surface tectonic deformation occurring before the broad uplift of the basin center is suggested by the surface topography and radar reflectors in the Mare Serenitatis.

Scott, D. H.↗
NASA NTRS1988

Space-Spurred Metallized Materials

Among a score of applications for a space spinoff reflective material called TXG is the emergency blanket manufactured by Metallized Products, Inc. Used by ski patrol to protect a skier shaken by a fall, the blanket retains up to 80% of user's body heat preventing post accident shock or chills. Carried by many types of emergency teams, blanket is large when unfolded, but folds into a package no larger than a deck of cards. Many other uses include, emergency blankets, all weather blanket, tanning blanket, window shields, radar reflector life raft canopies, etc.

Source record↗
NASA NTRS2006

Minimum mass design of large-scale space trusses subjected to thermal gradients

Lightweight, deployable trusses are commonly used to support space-borne instruments including RF reflectors, radar panels, and telescope optics. While in orbit, these support structures are subjected to thermal gradients that vary with altitude, location in orbit, and self-shadowing. Since these instruments have tight dimensional-stability requirements, their truss members are often covered with multi-layer insulation (MLI) blankets to minimize thermal distortions. This paper develops a radiation heat transfer model to predict the thermal gradient experienced by a triangular truss supporting a long, linear radar panel in Medium Earth Orbit (MEO). The influence of self-shadowing effects of the radar panel are included in the analysis, and the influence of both MLI thickness and outer covers/coatings on the magnitude of the thermal gradient are formed into a simple, two-dimensional analysis. This thermal model is then used to size and estimate the structural mass of a triangular truss that meets a given set of structural requirements.

thermal truss analysis↗