Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ROUGHNESS”

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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Scattering from rough surfaces

Electromagnetic wave scattering from rough surfaces, discussing radar return differences for different polarizations

Moore, R. K.↗
NASA NTRS1972

Turbulent-boundary-layer development on a moving ground belt of rough texture

The equations presented can be used to predict the shape factor and the ratio of the momentum thickness to the relative momentum thickness with reasonable accuracy for a moving ground belt provided that the stationary quantities are known and the two following basic approximations are valid: (1) Shape factor based upon velocity relative to the ground belt is nearly independent of the ratio of belt velocity to free-stream velocity. (2) The ratio of moving-belt momentum thickness to stationary-belt momentum thickness is independent of the coordinate measured in the streamwise direction. In addition, the integral quantities, momentum thickness and displacement thickness, can be predicted for the moving ground belt by using an empirically determined polynomial whose coefficients will change with different belt roughnesses.

Roper, A. T.↗
NASA NTRS1972

A study of radiometric emission from a rough sea surface

The equations which describe the emissivity of a rough ocean surface are developed. The theory includes effects of large scale and small scale wave structure and the influence of shadowing by the large ocean waves. Also included are investigations of the emission properties of foam and the influence of the thermal boundary layer on the brightness temperature characteristics of the ocean surface.

Stogryn, A.↗
NASA NTRS1972

Microwave emission measurements of sea surface roughness, soil moisture, and sea ice structure

In order to demonstrate the feasibility of the microwave radiometers to be carried aboard the Nimbus 5 and 6 satellites and proposed for one of the earth observatory satellites, remote measurements of microwave radiation at wavelengths ranging from 0.8 to 21 cm have been made of a variety of the earth's surfaces from the NASA CV-990 A/C. Brightness temperatures of sea water surfaces of varying roughness, of terrain with varying soil moisture, and of sea ice of varying structure were observed. In each case, around truth information was available for correlation with the microwave brightness temperature. The utility of passive microwave radiometry in determining ocean surface wind speeds, at least for values higher than 7 meters/second has been demonstrated. In addition, it was shown that radiometric signatures can be used to determine soil moisture in unvegetated terrain to within five percentage points by weight. Finally, it was demonstrated that first year thick, multi-year, and first year thin sea ice can be distinguished by observing their differing microwave emissivities at various wavelengths.

Gloersen, P.↗
NASA NTRS1971

Mapping sea-surface roughness using microwave radiometry.

Microwave radiometry data (1.55 cm) taken by aircraft over the Salton Sea have been corrected for viewing angle and atmospheric effects, rectified, and mapped. No fetch-limited conditions are observed along the upwind shore despite a 15 m/sec wind, which indicates that the radiometer is sensitive to the short wavelength surface roughness but not to the longer wavelengths. The brightness temperature field can be represented as a nearly linear function of the surface wind speed.

Strong, A. E.↗
NASA NTRS1972

Radar mapping of lunar surface roughness.

Comparison of anomalous behavior at infrared and radar wavelengths provides an estimation of lunar surface structure at centimeter-to-meter sizes. Although a simple classification is used, it is shown that the combination of the infrared and radar data contains more information than any of the sets by themselves. The infrared data indicate that bare surface rocks are the source of the roughness which generates enhanced radar backscatter. The different radar maps indicate the size of surface rocks, as was demonstrated for the strewn fields of centimeter-sized rubble (the Type II anomaly). As craters age, they have a rim-bright appearance in the radar maps, and eventually lose their anomalous-behavior at infrared and 3.8-cm radar wavelengths.

Thompson, T. W.↗
NASA NTRS1972

Theoretical analysis of rough-surface shadowing from point-source radiation.

The shadowing function, defined as the probability that a point on a rough surface will be illuminated by radiation from a source at fixed height above the surface, is considered. An exact expression for this probability is derived and evaluated approximately when the surface elevation is a normal random process. The effect of surface correlation is considered and shown to be appreciable. Several numerical computations of the shadowing function are presented.

Hardin, J. C.↗
NASA NTRS1972

Characteristics of ocean-reflected short radar pulses with application to altimetry and surface roughness determination

Current work related to geodetic altimetry is summarized. Special emphasis is placed on the effects of pulse length on both altimetry and sea-state estimation. Some discussion is also given of system tradeoff parameters and sea truth requirements to support scattering studies. The problem of analyzing signal characteristics and altimeter waveforms arising from rough surface backscattering is also considered.

Miller, L. S.↗
NASA NTRS1973

The problem of a finite strip compressed between two rough rigid stamps

A finite strip compressed between two rough rigid stamps is considered. The elastostatic problem is formulated in terms of a singular integral equation from which the proper stress singularities at the corners are determined. The singular integral equation is solved numerically to determine the stresses along the fixed ends of the strip. The effect of material properties and strip geometry on the stress intensity factor is presented graphically.

Gupta, G. D.↗
NASA NTRS1973

A high frequency correction to the Kirchhoff approximation, with application to rough surface EM wave scattering

A high frequency correction to the Kirchhoff approximation is developed for application to rough surface scattering. An approximate solution to the magnetic field integral equation for perfect conductivity and plane wave excitation yields a perturbed surface current expressed as a linear function of the second derivatives of surface height. The corrected surface current vector is substituted into the far field Stratton-Chu integral and average backscattered powers for the four polarization combinations are computed on the assumption that the surface is describable as a stationary Gaussian random process. The strength of this scattering solution is that it can account for height curvature correlation without requiring small height and slope.

Jackson, F. C.↗
NASA NTRS1973

Backscattering from a two-scale rough surface with application to radar sea return

A two-scale composite surface scattering theory was developed without using the noncoherent assumption. The surface is assumed electrically homogeneous and finitely conducting; the surface roughness may be nonuniform geometrically. The special forms of the terms for excluding the non-coherent assumption and the meanings of these terms are discussed. To gain insight into the mechanisms of backscattering, the results are compared with those obtained by previous theories. The comparison with NRL data shows satisfactory agreement for both horizontal and vertical polarization, especially for incident angles larger than 30 deg. For smaller incident angles, NASA/JSC data have been chosen for comparison and close agreement is again observed.

Chan, H. L.↗