Search NASA⌕ Search

SEARCH · Search NASA

Results for “'Polarimetric”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Application of Cloude's target decomposition theorem to polarimetric imaging radar data

In this paper we applied Cloude's decomposition to imaging radar polarimetry. We show in detail how the decomposition results can guide the interpretation of scattering from vegetated areas. For multifrequency polarimetric radar measurements of a clear-cut area, the decomposition leads us to conclude that the vegetation is probably thin compared to even the C-band radar wavelength of 6 cm. For a frosted area, we notice an increased amount of even number of reflection scattering at P-band and L-band, probably the result of penetration through the coniferous canopy resulting in trunk-ground double reflection scattering. However, the scattering for the forested area is still dominated by scattering from randomly oriented cylinders. It is found that these cylinders are thicker than in the case of clear-cut areas, leading us to conclude that scattering from the branches probably dominates in this case.

Vanzyl, Jakob J.↗
NASA NTRS1992

Processing of polarimetric SAR data for soil moisture estimation over Mahantango watershed area

Microwave remote sensing technique has a high potential for measuring soil moisture due to the large contrast in dielectric constant of dry and wet soils. Recent work by Pults et al. demonstrated the use of X/C-band data for quantitative surface soil moisture extraction from Airborne Synthetic Aperture Radar (SAR) system. Similar technique was adopted using polarimetric SAR data acquired with the JPL-AIRSAR system over the Mahantango watershed area in central Pennsylvania during July 1990. The data sets reported include C-, L-, and P-bands of 10, 13, 15, and 17 July 1990.

Rao, K. S.↗
NASA NTRS1993

Application of Cloude's target decomposition theorem to polarimetric imaging radar data

We apply Cloude's decomposition to imaging radar polarimetry. We derive the general expressions for the eigenvalues and eigenvectors for the case of terrain with reflection symmetry, and show in detail how the decomposition results can guide the interpretation of scattering from vegetated areas. For multi-frequency polarimetric radar measurements of a clear-cut area, the decomposition leads us to conclude that the vegetation is probably thin compared to even the C-band radar wavelength of 6 cm. For a forested area, we notice an increased amount of even number of reflection scattering at P-band and L-band, probably the result of penetration through the coniferous canopy resulting in trunk-ground double reflection scattering. The scattering for the forested area is still dominated by scattering from randomly oriented cylinders, however. It is found that these cylinders are thicker than in the case of clear-cut areas, leading us to conclude that scattering from the branches probably dominate in this case.

Vanzyl, Jakob J.↗
NASA NTRS1993

Polarimetric thermal emission from periodic water surfaces

Experimental results and theoretical calculations are presented to study the polarimetric emission from water surfaces with directional features. For our ground-based Ku-band radiometer measurements, a water pool was constructed on the roof of a building in the Jet Propulsion Laboratory, and a fiberglass surface with periodic corrugations in one direction was impressed on the top of the water surface to create a stationary water surface underneath it. It is observed that the measured Stokes parameters of corrugated fiberglass-covered water surfaces are functions of azimuth angles and agree very well with the theoretical calculations. The theory, after being verified by the experimental data, was then used to calculate the Stokes parameters of periodic surfaces without fiberglass surface layer and with rms height of the order of wind-generated water ripples. The magnitudes of the azimuthal variation of the calculated emissivities at horizontal and vertical polarizations corresponding to the first two Stokes parameters are found to be comparable to the values measured by airborne radiometers and SSM/I. In addition, the third Stokes parameter not shown in the literature is seen to have approximately twice the magnitude of the azimuth variation of either T(sub h) or T(sub v), which may make it more sensitive to the row direction, while less susceptive to noises because the atmospheric and system noises tend to be unpolarized and are expected to be cancelled out when the third Stokes parameter is derived as the difference of two or three power measurements, as indicated by another experiment carried out at a swimming pool with complicated surroundings. The results indicate that passive polarimetry is a potential technology in the remote sensing of ocean wind vector which is a crucial component in the understanding of global climate change. Issues related to the application of microwave passive polarimetry to ocean wind are also discussed.

Yueh, S. H.↗
NASA NTRS1994

Three-frequency, polarimetric, airborne SAR observations of the Greenland ice sheet

Synthetic aperture radar (SAR) images of the Greenland ice sheet collected by an airborne system clearly reveal the four melting facies of this sheet defined 30 years ago from snow stratigraphy studies by glaciologists. In particular, the radar echoes from the percolation facies have radiometric and polarimetric characteristics that are unique among terrestrial surfaces, but that resemble the exotic radar echoes recorded from the icy Galilean satellites. There, the radar signals interact with subsurface, massive ice features created in the cold, dry snow by seasonal melting and refreezing events. The subsurface features act as efficient reflectors of the incident radiation most likely via internal reflections. In the soaked-snow facies, the radar reflectivity is much lower because radar signals are attenuated by the wetter snow before they can interact with subsurface structures. Inversion algorithms to derive geophysical information from the SAR data are developed in both cases to estimate snow wetness in the soaked-snow facies and the mass of ice water retained in the percolation facies.

Rignot, E.↗
NASA NTRS1993

Field observations using an AOTF polarimetric imaging spectrometer

This paper reports preliminary results of recent field observations using a prototype acousto-optic tunable filter (AOTF) polarimetric imaging spectrometer. The data illustrate application potentials for geoscience. The operation principle of this instrument is different from that of current airborne multispectral imaging instruments, such as AVIRIS. The AOTF instrument takes two orthogonally polarized images at a desired wavelength at one time, whereas AVIRIS takes a spectrum over a predetermined wavelength range at one pixel at a time and the image is constructed later. AVIRIS does not have any polarization measuring capability. The AOTF instrument could be a complement tool to AVIRIS. Polarization measurement is a desired capability for many applications in remote sensing. It is well know that natural light is often polarized due to various scattering phenomena in the atmosphere. Also, scattered light from canopies is reported to have a polarized component. To characterize objects of interest correctly requires a remote sensing imaging spectrometer capable of measuring object signal and background radiation in both intensity and polarization so that the characteristics of the object can be determined. The AORF instrument has the capability to do so. The AOTF instrument has other unique properties. For example, it can provide spectral images immediately after the observation. The instrument can also allow observations to be tailored in real time to perform the desired experiments and to collect only required data. Consequently, the performance in each mission can be increased with minimal resources. The prototype instrument was completed in the beginning of this year. A number of outdoor field experiments were performed with the objective to evaluate the capability of this new technology for remote sensing applications and to determine issues for further improvements.

Cheng, Li-Jen↗
NASA NTRS1993

Polarimetric radar data decomposition and interpretation

Significant efforts have been made to decompose polarimetric radar data into several simple scattering components. The components which are selected because of their physical significance can be used to classify SAR (Synthetic Aperture Radar) image data. If particular components can be related to forest parameters, inversion procedures may be developed to estimate these parameters from the scattering components. Several methods have been used to decompose an averaged Stoke's matrix or covariance matrix into three components representing odd (surface), even (double-bounce) and diffuse (volume) scatterings. With these decomposition techniques, phenomena, such as canopy-ground interactions, randomness of orientation, and size of scatters can be examined from SAR data. In this study we applied the method recently reported by van Zyl (1992) to decompose averaged backscattering covariance matrices extracted from JPL SAR images over forest stands in Maine, USA. These stands are mostly mixed stands of coniferous and deciduous trees. Biomass data have been derived from field measurements of DBH and tree density using allometric equations. The interpretation of the decompositions and relationships with measured stand biomass are presented in this paper.

Sun, Guoqing↗
NASA NTRS1994

On the polarimetric variability of Y Cygni

The behavior of the B-band polarimetric data of Y Cygni is analyzed. A period search of the data indicates that the only significant periods arise due to the frequency with which the system had been observed. Around the eclipsing phases there is evidence to suggest that the primary star possesses a stellar wind. speculations regarding the possible envelope geometry are also commented upon.

Fox, G. K.↗
NASA NTRS1994

Radio continuum polarimetric imaging of high redshift radio galaxies

Multifrequency images of total and polarized radio continuum emission from the two high redshift radio galaxies 0902+343 (z = 3.40) and 0647+415 (4C 41.17, z = 3.80) are presented. These images represent the most sensitive polarimetric study of high redshift ratio galaxies to date. The emission from both galaxies is substantially polarized, up to 30% in some regions, and both sources sit behind deep 'Faraday screens,' producing large rotation measures, over 10(exp 3) rad/sq. m in magnitude, and large rotation measure gradients across the sources. Such large rotation measures provide further evidence that high redshift radio galaxies are situated in very dense environments. Drawing the analogy to a class of low redshift powerful radio galaxies with similarly large rotation measures, we suggest that 0902+343 and 0647+415 are situated at the centers of dense, x-ray 'colling flow' clusters, and that the cluster gas is substantially magnetized. The remarkable similarity between the optical and radio morphologies of 0647+415 on scales as small as 0.1 sec is presented. We consider, and reject, both synchrotron and inverse Compton radiation as possible sources of the optical emission. We also consider both scattering of light out of a 'cone' of radiation from an obscured nucleus, and jet-induced star formation, and find that both models encounter difficulties in explaining this remarkably close radio-optical alignment. High resolution spectral index images reveal compact, flat spectrum components in both sources. We suggest that these components are the active nuclei of the galaxies. Lastly, high resolution images of 0902+343 show that the southernmost component forms a 'ring' of 0.2 sec radius. We discuss the possibility that this ring is the result of gravitational lensing, along the lines proposed by Kochanek & Lawrence (1990).

Carilli, C. L.↗
NASA NTRS1995

Computing Thickness Of Sea Ice From Polarimetric SAR Data

Artificial neural network developed for computing thickness of sea ice from polarimetric synthetic-aperture-radar (SAR) data. Once neural network trained, no further intervention needed: when stimulated with SAR scattering data, quickly responds with estimate of thickness of sea ice.

Huynh, Dave D.↗
NASA NTRS1995

Mapping Vegetative Ground Cover From Polarimetric SAR Data

Three-frequency quad-polarization data used to distinguish among different types of cover. MAPVEG computer program performs first-level classification of NASA/JPL AIRSAR polarimetric synthetic-aperture-radar (SAR) data into simple ground-cover types. Classification images generated used to separate vegetated from nonvegetated areas; useful in determining soil moisture in areas free of vegetation. Classification separates forests from surrounding vegetation, and used to identify clear-cut areas. Urban areas and potential marshlands examples of other identifiable classes. Written in FORTRAN 77.

Chapman, Bruce↗
NASA NTRS1995

Calibrating Polarimetric Radar With Only Natural Targets

Method of calibrating polarimetric radar images involves use of natural, distributed targets only; no need to place artificial point calibration targets like corner-cube reflectors in target scene. Method based on few simplifying mathematical assumptions that, in turn, based on known electromagnetic-scattering characteristics of natural targets.

Yueh, Simon H.↗
NASA NTRS1995

Program Classifies Multiple-Frequency Polarimetric SAR Data

POLMAP computer program classifies multifrequency, polarimetric synthetic-aperture-radar (SAR) data into homogeneous classes of radar back-scatter. Software implements maximum-a-posteriori classification scheme. Performs by use of simulated-annealing procedure, takes much longer to compute than ICM solution, but it maximizes posteriori distribution of classes for whole scene. Input statistics of image classes must be created by some independent means, and supplied as input to POLMAP. Used as input to image processing application program. Written in FORTRAN 77.

Rignot, Eric↗
NASA NTRS1996

Dust Around Herbig Ae Stars: Additional Constraints from their Photometric and Polarimetric Variability

For the Herbig Ae stars with Algol-like minima (UX Ori, WW Vul, etc), the effects of circumstellar dust include: excess infrared emission, anomalous ultraviolet extinction, the 'blueing' of the stars in minima accompanying by an increase of intrinsic polarization. Using a Monte-Carlo code for polarized radiation transfer we have simulated these effects and compared the results obtained for different models with the observational data available. We found that the photometric and polarimetric behavior of the stars provided essential additional constraints on the circumstellar dust models. The models with spheroidal shell geometry and compact (non-fluffy) dust grains do not appear to be able to explain all the data.

Krivova, N. A.↗
NASA NTRS1996

Modeling Wetland Vegetation using Polarimetric SAR

A three-year project to study small-scale topographic changes and relict geomorphic features on barrier islands using synthetic aperture radar (SAR) is described. A study area on the Texas coast consisting of Galveston Island and Bolivar Peninsula was overflown by the NASA/JPL DC 8 AIRSAR in April 1995. Data was acquired in the fully polarimetric mode using C-, L-, and P-bands and in the TOPSAR configuration with C- and L-bands in interferometric mode. The study area will be overflown again in late spring 1996. The data will be registered to global positioning system (GPS) surveyed points to form high resolution digital elevation models (DEM) and then analyzed to investigate possible topographic changes.

Slatton, K. Clint↗
NASA NTRS1997

The polarimetric capabilities of NICMOS

The polarimetric capabilities of Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) are demonstrated from data obtained during the Early Release Observations of IRC+10216 and CRL 2688 (the Egg Nebula). Preflight Thermal Vacuum tests revealed that each polarizer has a unique polarizing efficiency, and that the position angle offsets differ from the nominal positions of O deg, 120 deg and 240 deg. Therefore an algorithm different from that of an ideal polarizer is required for proper reduction of astronomical polarimetry data. We discuss this new algorithm and the results of its application to NICMOS data. We also present preliminary estimates of the Instrumental Polarization, the sensitivity of the grisms to polarized light, and the accuracy of NICMOS imaging polarimetry for faint and low polarization objects. Finally, we suggest strategies for maximizing the success of NICMOS polarimetry observations.

Hines, D. C.↗
NASA NTRS1998

Near Simultaneous Spectroscopic and Polarimetric Observations of Be Stars

Near simultaneous optical spectroscopic (on four nights) and linear continuum (B, V, R and I bands) polarimetric (on seven nights) observations of 29 Be stars were carried out during November - December 1993. The program Be stars displayed wavelength dependence of intrinsic polarizations with no frequency dependence of position angles. Measured values of linear intrinsic polarizations of these Be stars were all less than 1.6%. The Be and Be-shell stars displayed no clear distinction in their polarization values. Observed polarizations at B, V, R and I bands were compared with the theoretically computed linear polarization values of the program stars. It has been suggested that these observed polarizations indicate that the envelopes of the Be stars may have a range of oblateness. Early-type Be stars displayed relatively higher polarizations than the late-type ones. Full widths at half intensity maximum of H(sub alpha) profiles and the intrinsic linear continuum polarizations are closely correlated with the projected rotational velocities of the program stars. Photospheric-absorption-corrected equivalent widths of H(sub alpha), profiles [W((alpha)] and the radii of H(sub alpha) emitting envelopes (R(sub e)) are non-linearly correlated with the intrinsic continuum polarizations of these stars. However, W((alpha) and R(sub e) are linearly correlated. Detail discussion of these results are presented in this paper.

Ghosh, K. K.↗
NASA NTRS1998

Three-Dimensional Road Network by Fusion of Polarimetric and Interferometric SAR Data

In this paper a fuzzy classification procedure is applied to polarimetric radar measurements, and street pixels are detected. These data are successively grouped into consistent roads by means of a dynamic programming approach based on the fuzzy membership function values. Further fusion of the 2D road network extracted and 3D TOPSAR measurements provides a powerful way to analyze urban infrastructures.

Gamba, P.↗