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Results for “RADAR SCATTERING”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Incoherent Scatter Radar Studies of the Mesosphere

All current incoherent backscatter radars can make mesospheric or D region measurements under at least some conditions. The conditions under which measurements are possible are derived and shown for each radar. Conditions examined include overall system sensitivity, electron and ion spectral line widths and power distributions, and time/height averaging effects. The radar equations is derived and calibrations of the radar system is discussed. Total power only and combined total power and ion line spectral measurements are described in terms of ease of use, applicability to various radars, and parameters of aerodynamic interest derivable from the measurements.

Mathews, J. D.↗
NASA NTRS1988

Radar scattering and soil moisture

Research is being conducted on microwave scattering from vegetation. The objective is to develop techniques for measuring parameters of the vegetation canopy (such as biomass) needed for understanding global biogeochemical cycles and to develop techniques for correcting microwave measurements of soil moisture for the effects of the vegetation canopy. Measurements of vegetation and soil moisture are important for understanding the environment on a global scale. For example, moisture in the soil is an important, highly variable, element in the global hydrologic cycle. The hydrologic cycle, in turn, is strongly coupled to weather and climate through moisture (and energy) fluxes at the surface. The amount and distribution of vegetation is an important element in biogeochemical cycles; and knowledge of both the vegetation canopy and soil moisture is of practical importance in agricultural management. These theories are examined.

Levine, D. M.↗
NASA NTRS1989

Wavelet analysis introduction and application to radar scattering from water waves

Double-parameter expansions, leading to an instantaneous multiscale analysis, are used to obtain time-frequency graphs from time-series data for interpretation of scatterometer response to sea surface geometry. This method is used to define, as well as possible, one-dimensional signal input (elevation and slope). However, some important fundamental parameters, such as the asymmetric development of short scales in crests and troughs, the long-wave amplitude modulation, the different zero-crossings, and so forth, are easily extracted from the wavelet images.

Chapron, B.↗
NASA NTRS1992

The dynamic cusp at low altitudes: A case study combining Viking, DMSP, and Sondrestrom incoherent scatter radar observations

A case study involving data from three satellites and a ground-based radar are presented. Focus is on a detailed discussion of observations of the dynamic cusp made on 24 Sep. 1986 in the dayside high-latitude ionosphere and interior magnetosphere. The relevant data from space-borne and ground-based sensors is presented. They include in-situ particle and field measurements from the DMSP-F7 and Viking spacecraft and Sondrestrom radar observations of the ionosphere. These data are augmented by observations of the IMF and the solar wind plasma. The observations are compared with predictions about the ionospheric response to the observed particle precipitation, obtained from an auroral model. It is shown that observations and model calculations fit well and provide a picture of the ionospheric footprint of the cusp in an invariant latitude versus local time frame. The combination of Viking, Sondrestrom radar, and IMP-8 data suggests that we observed an ionospheric signature of the dynamic cusp. Its spatial variation over time which appeared closely related to the southward component of the IMF was monitored.

Watermann, Jurgen↗
NASA NTRS1999

High-Latitude Incoherent-Scatter Radar Measurements for the ISTP Program

Over the course of this contract, the ISTP mission became a reality and proved to be one of NASA's success stories. SRI and the NSF-sponsored Sondrestrom radar contributed significantly to the success. We provided dedicated radar experiment time with operation modes specifically designed to complement the ISTP spacecraft. Data collected during coronal mass ejection events indicated that at times significant energy is fed from the ionosphere to the magnetosphere. A model of global conductance is emerging from combined POLAR and Sondrestrom data sets. We initiated a study to investigate the behavior of the global energy budget during the evolution of magnetospheric storms and substorms using a number of ground-based and satellite data sets.

Kelly, John D.↗
NASA NTRS2001

Near-Nadir Radar Scattering from Venus

Analysis of Magellan altimeter data using a fractal-surface scattering model. Additional information is contained in the original extended abstract.

Campbell, Bruce A.↗
NASA NTRS1999

MOLA-derived Roughness Data Used to Predict Surface Scattering for Mars Subsurface Radar Sounding

The Mars Express orbiter, to be launched by the European Space Agency in 2003, will carry a low-frequency radar sounding instrument, MARSIS (Mars Advanced Radar for Subsurface and Ionospheric Sounding). The primary goal of MARSIS is to map the distribution of water, both solid and (if present) liquid, in the upper several km of the martian crust. Detecting discontinuities in the crust, such as an ice-water transition, presents many challenges for a Mars orbital radar sounder. One challenge that must be overcome is the presence of radar scattering (echoes) from the surface of Mars, expected to be detected by the sounder antennas at the same time as any echoes aris-ing from subsurface interfaces. As the transmitted spherical wavefront spreads within the crust of Mars,. it also interacts with surface topography at off-nadir positions, creating a "clutter" signal that can mask the subsurface echoes. The MARSIS instrument will utilize Doppler filtering to limit the off-nadir clutter in the along-track direction, and a nadir-null secondary antenna to identify strong off-nadir clutter from the cross-track direction. To evaluate the effects of off-nadir surface clutter and the capability of these schemes to reduce the clutter, it is necessary to predict the range of scattering behavior that may be expected from martian surface topography. In this paper, we utilize Mars Orbital Laser Altimeter (MOLA) data from the current Mars Global Surveyor mission to characterize the topographic roughness of a variety of martian terrain types, at scales relevant to the MARSIS clutter problem. Segments of MOLA altimetry profiles are reduced to the topographic parameters rms slope and fractal dimension, which then are used as inputs to a near-nadir radar scattering model to predict the strength of the clutter signal. Additional information is contained in the original extended abstract.

Plaut, J. J.↗
NASA NTRS2004

Measurements of Ocean Surface Scattering Using an Airborne 94-GHz Cloud Radar: Implication for Calibration of Airborne and Spaceborne W-band Radars

Scattering properties of the Ocean surface have been widely used as a calibration reference for airborne and spaceborne microwave sensors. However, at millimeter-wave frequencies, the ocean surface backscattering mechanism is still not well understood, in part, due to the lack of experimental measurements. During the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE), measurements of ocean surface backscattering were made using a 94-GHz (W-band) cloud radar onboard a NASA ER-2 high-altitude aircraft. The measurement set includes the normalized Ocean surface cross section over a range of the incidence angles under a variety of wind conditions. Analysis of the radar measurements shows good agreement with a quasi-specular scattering model. This unprecedented dataset enhances our knowledge about the Ocean surface scattering mechanism at 94 GHz. The results of this work support the proposition of using the Ocean surface as a calibration reference for airborne millimeter-wave cloud radars and for the ongoing NASA CloudSat mission, which will use a 94-GHz spaceborne cloud radar for global cloud measurements.

Li, Li-Hua↗
NASA NTRS1965

Scattering theories and radar return

Scattering theories and radar return - theory of bistatic radar return from statistically rough surface and literature survey on scattering theories

SURFACE ROUGHNESS↗
NASA NTRS1999

Estimating Vegetation Parameters from Interferometric and Polarimetric Radar Using Physical Scattering Models

Radar data from vegetated land surfaces depend on many structural and compositional parameters describing the terrain. Because early, noninterferometric radar systems usually constituted an insufficient observation set from which to estimate parameters of the terrain, statistical regression techniques were used which incorporated some level of apriori knowledge or field measurements. With the advent of radar interferometry and polarimetric interferometry, potentially at multiple baselines, the observation set is now approaching that required to quantitatively estimate the parameters describing a vegetated land surface. Quantitative estimation entails formulating a physical scattering model relating the radar observations to the vegetation and surface parameters on which they depend. This paper describes the physics of candidate scattering models, and shows how the models determine the estimable parameter set. It also indicates the measurement accuracy of parameters such as vegetation height, height-to-base-of-live-crown, and surface topography with multibaseline polarimetric interferometry.

Treuhaft, Robert N.↗
NASA NTRS1978

The calculated and observed ionospheric properties during Atmospheric Explorer-C satellite crossings over Millstone Hill

Results are presented for calculated and observed incoherent scatter radar data on ionospheric and atmospheric properties during the crossings of the Atmospheric Explorer-C satellite over the Millstone Hill, Massachusetts incoherent scatter radar station. The incoherent scatter radar measured electron density vertical profiles and electron and ion temperatures. These values yielded the exospheric temperature and the vertical distribution of neutral gas temperature. The satellite measured electron and ion temperatures and densities, neutral gas composition, and photoelectron spectra. Measurements were also made of solar UV and EUV fluxes, the vertical profile of the NO number density, and the vertical profile of the 6300 A airglow-volume emission rate. The results are compared to those of a time-dependent coupled model of the ionospheric E- and F-regions. Good agreement is found between satellite results, incoherent scatter radar measurements, and model calculations. Along the orbital path satellite measurements show significant latitudinal gradients in the measured properties.

Roble, R. G.↗
NASA NTRS2003

Fault Creep along the Southern San Andreas from Interferometric Synthetic Aperture Radar, Permanent Scatterers, and Stacking

Interferometric synthetic aperture radar (InSAR) provides a practical means of mapping creep along major strike-slip faults. The small amplitude of the creep signal (less than 10 mm/yr), combined with its short wavelength, makes it difficult to extract from long time span interferograms, especially in agricultural or heavily vegetated areas. We utilize two approaches to extract the fault creep signal from 37 ERS SAR images along the southem San Andreas Fault. First, amplitude stacking is utilized to identify permanent scatterers, which are then used to weight the interferogram prior to spatial filtering. This weighting improves correlation and also provides a mask for poorly correlated areas. Second, the unwrapped phase is stacked to reduce tropospheric and other short-wavelength noise. This combined processing enables us to recover the near-field (approximately 200 m) slip signal across the fault due to shallow creep. Displacement maps fiom 60 interferograms reveal a diffuse secular strain buildup, punctuated by localized interseismic creep of 4-6 mm/yr line of sight (LOS, 12-18 mm/yr horizontal). With the exception of Durmid Hill, this entire segment of the southern San Andreas experienced right-lateral triggered slip of up to 10 cm during the 3.5-year period spanning the 1992 Landers earthquake. The deformation change following the 1999 Hector Mine earthquake was much smaller (4 cm) and broader than for the Landers event. Profiles across the fault during the interseismic phase show peak-to-trough amplitude ranging from 15 to 25 mm/yr (horizontal component) and the minimum misfit models show a range of creeping/locking depth values that fit the data.

Lyons, Suzanne↗