Roughness effects on heat transfer in the supersonic region of a conical nozzle
Conical nozzle roughness on heat transfer in supersonic region
Reshotko, M.↗
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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.↗
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.↗
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.↗
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.↗
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.↗
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.↗
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.↗
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.↗
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.↗
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.↗
Surface roughness measured by optical signatures
To measure roughness of metal surfaces by nondestructive means direct laser beam at surface and record distribution pattern of intensity of reflected light to obtain optical signature for comparison with calibrated surface. Signature of machined surface with scratch compared to that of regularly-patterned machined surface may also detect imperfections.
Salvinski, R. J.↗
The influence of steel roughness and granulation on the accuracy of part thickness measurement by means of ultrasounds
Nondestructive measurement of the thickness of one-sided parts can be successfully conducted with the aid of ultrasounds. Using an ultrasonic defectoscope equipped with a highly precise device for thickness measurement, the experimental results obtained and the parameters that influence them are discussed. It is known that the manner of attaching the probe to the surface to be tested is influenced by the roughness of the surface. Likewise, in view of the fact that measurement results are influenced by the velocity of ultrasounds in the material to be investigated, they are also conditioned by the size of the structure. These factors and the manner in which they influence measurement results are also described.
Sontea, S.↗
Imaging radars provide terrain texture and roughness parameters in semi-arid environments
Geoscience potentialities and limitations of available imaging radars are examined for alluvial valley-playa terrain environments. In such arid environments, a dual-sensor combination of an imaging radar with aerial photography is shown to provide a practical method for monitoring gross changes in surface textures of alluvial fans and playa surface conditions. It also appears feasible to infer surface materials and relative surface roughness with an improved degree of interpretive reliability.
Macdonald, H. C.↗
A theory of wave scatter from an inhomogeneous medium with a slightly rough boundary and its application to sea ice
An analytical theory of electromagnetic wave scattering from an inhomogeneous medium with a slightly rough boundary surface is formulated. The inhomogeneity in the medium is assumed to vary continuously in the vertical direction and to have a small random variation in the horizontal direction. The medium is assumed to consist of two layers. Maxwell's equations are solved by using the small perturbation method together with Fourier transform technique. The resulting differential equations are solved by using WKB and variation of parameter methods. Field amplitudes in each medium are determined by taking boundary conditions into account. The expressions for first order polarized radar backscatter cross-section are obtained. An attempt is made to apply the developed theory to compute sea ice scatter. Numerical calculations are performed for polarized radar backscatter cross-section at two frequencies, 13.3 GHz and 400 MHz. It is shown that WKB method is applicable at both of these frequencies. Theoretical results are compared with the experimental results obtained from NASA Earth Resources Program mission 126. Theoretical results and experimental results are in good agreement.
Parashar, S. K.↗
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.↗
Depolarization of light back scattered from rough dielectrics
The depolarization of laser light backscattered from inhomogeneous dielectrics was investigated both experimentally and theoretically. A theoretical model that includes backscattering from both the surface and subsurface was developed by use of the Kirchhoff approach. The subsurface polarized and depolarized backscattered components are independent of surface roughness. The model predicts results in agreement with experimental measurements performed with a dual-polarized laser backscattering system. The measurements indicate that a significant contribution to the total backscattered power results from subsurface contributions; in some cases, this contribution completely masks the effects due to the surface.
Wilhelmi, G. J.↗
A comparison of Skylab S-193 and aircraft views of surface roughness and a look toward SEASAT
An extensive aircraft underflight program was conducted along the Skylab groundpath for the purpose of documenting wind, wave, and atmospheric conditions affecting the amplitude of the active and passive microwave signatures. The S-193 microwave system senses a roughness parameter at the ocean surface that is proportional to the surface windspeed. The aircraft program is described, and some comparisons of satellite and aircraft results are presented. The principal result of the comparison of active radar is that direct inferences of the surface windspeed are possible, but subject to considerable scatter, and that this scatter appears to be due to interaction between long gravity and short Bragg waves and backscatter due to rain as well as errors in correcting for azimuth dependence. An unforeseen opportunity to observe a Pacific hurricane by both Skylab and NOAA aircraft has contributed to the development of a simplified wave forecasting scheme applicable to hurricanes, and more general conditions, which combines the better qualities of both spectral and height/period forecasting techniques. Horizontal polarization data obtained by the aircraft in Hurricane Ava, and in other experiments, which led to this development are presented.
Ross, D.↗