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At least 235 records · Page 13

All sources NASA NTRS DOE OSTI

NASA NTRS1970

Phenomenological approach to scatterometer data interpretation

A graphic method of analyzing radar scatterometer sea clutter data leading to linear relations between scattering cross sections and tan angle of incidence of the radiation is proposed. This relation permits formulation of simple analytic relations without reference to the ocean surface spectrum. Parameters introduced depend on the wavelength of the incident radiation and its polarization, and on wind and sea states. The simplicity of the expressions derived suggests a corresponding simplicity in the physical mechanism of radar sea clutter return.

Alzofon, F. E.↗

NASA NTRS1972

Frequency distributions of lunar slopes, part C

The metric and panoramic cameras aboard the Apollo 16 spacecraft provided photographs on which photogrammetric techniques may be used to obtain precise measurements of horizontal distances and elevations. It is reported that these measurements may in turn be used to obtain slope-frequency distributions of lunar surfaces at various slope lengths and for various types of terrain and geologic map units. Bistatic radar and photoclinometric methods were also used to obtain the same data.

Wu, S. S. C.↗

NASA NTRS1976

GEOS-C C-band transponder prelaunch calibration and test data

The delay characteristics and spacecraft telemetry housekeeping data for the GEOS-C C-Band transponders are presented. The data are presented in graphical form to provide a convenient method for computing radar range measurement corrections as a function of signal strength at the transponder and spacecraft environment. The data are also presented in tabular form along with the mathematical models used to derive the curves. Also included are a list of the operating characteristics of each transponder and a description of the calibration test equipment set-up.

Selser, A. R.↗

NASA NTRS1978

Image synthesis for SAR system, calibration and processor design

The Point Scattering Method of simulating radar imagery rigorously models all aspects of the imaging radar phenomena. Its computational algorithms operate on a symbolic representation of the terrain test site to calculate such parameters as range, angle of incidence, resolution cell size, etc. Empirical backscatter data and elevation data are utilized to model the terrain. Additionally, the important geometrical/propagation effects such as shadow, foreshortening, layover, and local angle of incidence are rigorously treated. Applications of radar image simulation to a proposed calibrated SAR system are highlighted: soil moisture detection and vegetation discrimination.

Holtzman, J. C.↗

NASA NTRS1978

Stereographic cloud heights from imagery of SMS/GOES satellites

Stereographic pairs of SMS/GOES images, generated simultaneously by the spin-scan cameras of each of two geostationary satellites (SMS 1 and SMS 2, separated by 32 degrees of longitude on February 17, 1975), have been analyzed photogrammetrically to yield cloud heights with a two-sigma uncertainty of 500 meters. The 32-degree angle between the image plane of the two satellites, plus the distortions involved in transferring the image of a nearly full hemisphere of the earth onto a plane, required the development of a special instrument to permit stereographic compilation. Cloud heights measured stereographically compared favorably with heights of the same clouds measured by radar and IR methods. The same SMS image pairs were used to measure mountain-top heights with a mean deviation of 0.24 km from cartographic values.

Minzner, R. A.↗

NASA NTRS1977

Stereographic cloud heights from SMS/goes imagery

Stereographic pairs of SMS/GOES images, generated simultaneously by the spin-scan cameras of each of two geostationary satellites (SMS 1 and SMS2), separated by 32 degrees of longitude on February 1, 1975, were analyzed photogrametrically to yield cloud heights with a two-sigma uncertainty of 500 meters. These cloud heights compare favorably with heights of the same clouds measured by radar and IR methods. The same SMS image pairs were used to measure mountaintop heights with a mean deviation of 0.24 km from cartographic values.

Minzner, R. A.↗

NASA NTRS1983

Inverting a dispersive scene's side-scanned image

Consideration is given to the problem of using a remotely sensed, side-scanned image of a time-variant scene, which changes according to a dispersion relation, to estimate the structure at a given moment. Additive thermal noise is neglected in the models considered in the formal treatment. It is shown that the dispersion relation is normalized by the scanning velocity, as is the group scanning velocity component. An inversion operation is defined for noise-free images generated by SAR. The method is extended to the inversion of noisy imagery, and a formulation is defined for spectral density estimation. Finally, the methods for a radar system are used for the case of sonar.

Harger, R. O.↗

NASA NTRS1984

The Adelaide VHF radar: Capabilities and future plans

The VHF radar at Buckland Park, South Australia commenced operation in January, 1984. The radar is located adjacent to the 2-MHz ionospheric radar. The routine method for measuring horizontal wind velocity is the space antenna technique (SA) while the Doppler technique is used to measure vertical velocities. It is possible to swing the transmitting beam in the east-west plane, allowing Doppler measurements of the EW wind component.

Briggs, B. H.↗

NASA NTRS1987

Photographic fireball networks

Long term radar observations of any meteor shower yield good data for a study of the features of its cross section structure in detail. The hourly rates of meteor echoes represent usually the basic data from which shower characteristics are derived. Unfortunately, the hourly rate does not depend only on the activity of the shower in question but also on the position of the shower radiant, on the mutual radiant antenna position, and on the parameters of the radar system. It is known that the knowledge of the response function of the radar is necessary for good interpretation of the hourly echo counts. A method of long term radar shower data analysis is discussed along with preliminary results.

Ceplecha, Z.↗

NASA NTRS1992

High resolution frequency to time domain transformations applied to the stepped carrier MRIS measurements

Two narrow-band radar systems are developed for high resolution target range estimation in inhomogeneous media. They are reformulations of two presently existing systems such that high resolution target range estimates may be achieved despite the use of narrow bandwidth radar pulses. A double sideband suppressed carrier radar technique originally derived in 1962, and later abandoned due to its inability to accurately measure target range in the presence of an interfering reflection, is rederived to incorporate the presence of an interfering reflection. The new derivation shows that the interfering reflection causes a period perturbation in the measured phase response. A high resolution spectral estimation technique is used to extract the period of this perturbation leading to accurate target range estimates independent of the signal-to-interference ratio. A non-linear optimal signal processing algorithm is derived for a frequency-stepped continuous wave radar system. The resolution enhancement offered by optimal signal processing of the data over the conventional Fourier Transform technique is clearly demonstrated using measured radar data. A method for modeling plane wave propagation in inhomogeneous media based on transmission line theory is derived and studied. Several simulation results including measurement of non-uniform electron plasma densities that develop near the heat tiles of a space re-entry vehicle are presented which verify the validity of the model.

Ardalan, Sasan H.↗

NASA NTRS1991

Suppressing interfering scattered signals in swept-frequency radar measurements by using frequency domain Wiener filtering

A novel approach to the reduction of scattered, interfering signals that corrupt measurements of the signal backscattered from radar targets of interest is being developed. It is being explored with sphere measurements in an indoor microwave radar range. This method is based on the concept of Wiener filtering (which minimizes the difference between the signal plus noise and the desired signal in the time domain). In contrast to the traditional Wiener filter, in which the time domain error between two sequences are minimized, the approach reported uses the frequency domain phasor amplitudes of a swept frequency signal. It minimizes the difference (least-mean-square-magnitude) between the signal-plus-noise and the signal complex phasors, across the entire spectrum.

Weissman, David E.↗

NASA NTRS1996

Calibration of NASA Turbulent Air Motion Measurement System

A turbulent air motion measurement system (TAMMS) was integrated onboard the Lockheed 188 Electra airplane (designated NASA 429) based at the Wallops Flight Facility in support of the NASA role in global tropospheric research. The system provides air motion and turbulence measurements from an airborne platform which is capable of sampling tropospheric and planetary boundary-layer conditions. TAMMS consists of a gust probe with free-rotating vanes mounted on a 3.7-m epoxy-graphite composite nose boom, a high-resolution inertial navigation system (INS), and data acquisition system. A variation of the tower flyby method augmented with radar tracking was implemented for the calibration of static pressure position error and air temperature probe. Additional flight calibration maneuvers were performed remote from the tower in homogeneous atmospheric conditions. System hardware and instrumentation are described and the calibration procedures discussed. Calibration and flight results are presented to illustrate the overall ability of the system to determine the three-component ambient wind fields during straight and level flight conditions.

Barrick, John D. W.↗

NASA NTRS1993

Three-Dimensional Reconstruction of Asteroids from Radar Observations

A program of research has recently been initiated under the NASA Innovative Research Program to develop and test techniques for reconstructing the three-dimensional shapes of asteroids from ground-based radar observations. Presently, no methods exist to do this and the full scientific potential of current radar data sets lies untapped. The situation will become even more pronounced in approximately two years when the upgraded Arecibo radar system becomes capable of regularly producing asteroid data sets with very fine spatial resolution and high signal-to-noise ratios. If successful, the proposed research will significantly increase our knowledge of these objects. The potential and limitations of the techniques developed will be rigorously tested in a series of computer simulations and optical scattering experiments with scale models.

Hudson, Scott↗

NASA NTRS2000

An Investigation of EME as a Potential Cause of Fuel Tank Ignition

NASA researchers were tasked to study the potential for radio signals to excite an aircraft fuel quantity indication system (FQIS) enough to cause arcing, sparking or excessive heating within a fuel tank. Computational techniques were used to determine the threat from external high intensity radiated field (HIRF) transmitters nearby, like shipboard and airborne RADAR systems. Experimental methods were used to determine the threat from Portable Electronic Devices (PEDs) carried aboard by passengers. To support this work, unique electromagnetic coupling measurements were performed on a retired Boeing 747 aircraft, and new test and analysis methods were developed that may be applied to other FQIS designs as well as other aircraft electronic systems.

Ely, Jay J.↗

NASA NTRS2011

Precipitation Estimates for Hydroelectricity

Hydroelectric plants require precise and timely estimates of rain, snow and other hydrometeors for operations. However, it is far from being a trivial task to measure and predict precipitation. This paper presents the linkages between precipitation science and hydroelectricity, and in doing so it provides insight into current research directions that are relevant for this renewable energy. Methods described include radars, disdrometers, satellites and numerical models. Two recent advances that have the potential of being highly beneficial for hydropower operations are featured: the Global Precipitation Measuring (GPM) mission, which represents an important leap forward in precipitation observations from space, and high performance computing (HPC) and grid technology, that allows building ensembles of numerical weather and climate models.

Tapiador, Francisco J.↗

DOE OSTI2015

Interferometric millimeter wave and THz wave doppler radar

A mixerless high frequency interferometric Doppler radar system and methods has been invented, numerically validated and experimentally tested. A continuous wave source, phase modulator (e.g., a continuously oscillating reference mirror) and intensity detector are utilized. The intensity detector measures the intensity of the combined reflected Doppler signal and the modulated reference beam. Rigorous mathematics formulas have been developed to extract bot amplitude and phase from the measured intensity signal. Software in Matlab has been developed and used to extract such amplitude and phase information from the experimental data. Both amplitude and phase are calculated and the Doppler frequency signature of the object is determined.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1969

Comments on Doppler radar applications

The application of Doppler methods to theoretical or meteorological problems is discussed. Research for using radar to study and monitor severe thunderstorms, turbulence, and tornadoes is recommended.

Kessler, E.↗

NASA NTRS1983

The application of near-nadir Delta-k radar techniques to geodetic altimetry and oceanographic remote sensing

This paper first examines the extension of two-frequency, or Delta-k near-nadir remote sensing techniques to off-nadir radar altimetry. A different approach to sea state sensing is investigated which appears to offer much higher accuracy. The second section examines the Delta-k method of sensing rough surface area correlation or ocean wavenumber spectrum. The technique shows promise of directly sensing this parameter, in contrast with synthetic-aperture radar methods which are based on complex wave interaction mechanisms and mathematical transformations requiring the acquisition of voluminous data.

Miller, L. S.↗