Wake and interreflection effects in the calculation of free molecular flow drag coefficients
Monte Carlo calculation of drag coefficients in free molecular flow with wake and reflection effects
Ballance, J. O.↗
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Results for “reflection coefficient”
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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Optical absorption in triphenylmethylarsonium tetracyanoquinodimethan single crystals.
Optical abosrption coefficients for triphenylmethylarsonium tetracyanoquinodimethan complex single crystal, evaluating reflectance
Mookherji, T.↗
Combined environmental effects on polymers
A series of space simulation tests on FEP Teflon and other polymeric thermal control coatings was conducted using UV, electrons, protons and Lyman-alpha wavelength vacuum UV radiation. Interest was centered on simulating synchronous altitude radiation environment conditions. Physical changes in materials included loss of specularity and introduction of a high density of photographable tracking defects on a microscopic scale. An example shows the discharge of trapped electrons when dielectric strength is exceeded. This leaves a portion of the Teflon volume no longer clear, but diffusely transmitting and reflecting. Thermophysical changes included degradation of solar absorptance coefficients as much as five-fold. The situation that prevails for earth orbit contrasted with polymer performance in the solar wind. It is suggested that conductive overcoatings be developed for polymers and other flexible materials, comparable or superior to those available for fused silica SSMs.
Fogdall, L. B.↗
Solar and atmospheric effects on satellite imagery derived from aircraft reflectance measurements
Solar and atmospheric effects on satellite imagery were investigated by measuring terrain reflectance from low-flying aircraft. Radiometric data were recorded over three test sites in California, Georgia, and South Dakota. Radiance from Skylab (EREP) S190A and ERTS-1 (Landsat-1) sensors was linearly correlated with wide-band terrain reflectance. The results support the proposition that the coefficients of the regression equation are the path radiance and a quantity representing the product of total irradiance and beam transmittance at the time of satellite overflight. These coefficients should be useful as linear conversion coefficients for extending spectral signatures in computer-aided classification work on satellite imagery.
Dana, R. W.↗
Instrument measures many optical properties in visible and IR
Electro-optical system measures reflectance, reflectance ratio, transmission, absorption, refractive index, and absorption coefficient in both visible and infrared (IR) spectral regions. System effectively combining capabilities of ellisometer, reflectometer, and spectrophotometer is expected to find application in environmental and material composition testing fields.
Batten, C. E.↗
Analytical description of an imperfect Fabry-Perot etalon
A novel method is presented for the investigation of Fabry-Perot etalon defects, incorporating the effects of microsurface imperfection, bowing, and departure from parallelism, as well as the effect of finite aperture on the etalon, into the perturbation function. The tolerance imperfections of reflective layers can be incorporated into the transfer coefficients of a noncorrugated thin-film system, and any defect can be investigated either separately or in combination with others through the use of the appropriate analytical or numerical simulation of the corrugated function. In the context of numerical computation, the present method permits the simulation and evaluation of different specific situations. The expressions derived for the transfer coefficients of a corrugated, equidistant thin film system may be applicable to other branches of applied optics.
Prikryl, I.↗
Optimal landing of a helicopter in autorotation
The landing of a helicopter in autorotation is formulated as a nonlinear optimal control problem. A unique feature in the present formulation is the addition of path inequality constraints on both the control and the state vectors. The control variable inequality constraint is a reflection of the limitation on the rotor thrust coefficient. The state-variable inequality constraint is an upper bound on the vertical sink-rate of the helicopter during descent. Optimal trajectories are calculated for entry conditions well within the height-velocity (H-V) restriction curve, with the helicopter initially in hover or in forward flight. The optimal solutions exhibited control techniques similar to those used by helicopter pilots in actual autorotational landings. The study indicates that, subject to pilot acceptability, a substantial reduction could be made in the H-V restriction zone using optimal control techniques.
Lee, A. Y.↗
Adhesives For Use In Vacuum, Radiation, And Cold
Report presents results of literature searches and tests of eight adhesives for use in high-radiation, low-temperature, vacuum environment of Galileo spacecraft mission to Jupiter. Used as bonding agents for thermal blankets, instruments, structural members, and coatings. Adhesives tested for contamination, reflectance, bond integrity, color, transmittance, outgassing, dielectric constant, coefficient of thermal expansion, optical interference, peel strength, and shear strength. Some of tests conducted at temperature of liquid nitrogen (-150 degree C).
Bouquet, Frank L.↗
A parametric study of bleed in shock boundary layer interactions
A numerical investigation was conducted to study the effect of bleed configuration on oblique-shock wave/turbulent boundary-layer interactions. Bleed is applied through a normal slot across the shock impingement location. The numerical solution to the compressible Navier-Stokes equations is obtained for the turbulent flow throughout the interaction zone and inside the bleed slot for bleed mass flow rates up to 57 percent of the boundary layer mass flow upstream of the interaction. The results indicate that the bleed slot performance improves as the slot width decreases and the length to width ratio increases. This is reflected as an increase in the bleed discharge coefficient and total pressure, and a reduction in the boundary layer momentum and displacement thickness downstream.
Hamed, A.↗
An alternative approach to estimating rainfall rate by radar using propagation differential phase shift
In this work it is shown that for frequencies from 3 to 13 GHz, the ratio of the specific propagation differential phase shift phi(sub DP) to the rainfall rate can be specified essentially independently of the form of the drop size distribution by a function only of the mass-weighted mean drop size D(sub m). This significantly reduces one source of substantial bias errors common to most other techniques for measuring rain by radar. For frequencies 9 GHz and greater, the coefficient can be well estimated from the ratio of the specific differential attenuation to phi(sub DP), while at nonattenuating frequencies such as 3 GHz, the coefficient can be well estimated using the differential reflectivity. In practice it appears that this approach yields better estimates of the rainfall rate than any other current technique. The best results are most likely at 13.80 GHz, followed by those at 2.80 GHz. An optimum radar system for measuring rain should probably include components at a both frequencies so that when signals at 13.8 GHz are lost because of attenuation, good measurements are still possible at the lower frequency.
Jameson, A. R.↗
A UGO/EUTD Solution for the Scattering and Diffraction from Cubic Polynomial Strips
A uniform geometrical optics (UGO) and an extended uniform geometrical theory of diffraction (EUTD) solution is developed for the scattering and diffraction from perfectly conducting cubic polynomial strips. The new solution overcomes the difficulties of the classic GO/UTD solution near caustics and composite shadow boundaries. The approach for constructing the UGO/EUTD solution is based on a spatial domain physical optics (PO) radiation integral representation for the scattered field which is then reduced using a uniform asymptotic procedure. New uniform reflection, zero-curvature diffraction, and edge diffraction coefficients are derived and involve the ordinary and incomplete Airy integrals as canonical functions. Higher order effects such as double edge diffraction, edge-excited creeping waves, and whispering gallery modes are not examined in this work. The UGO/EUTD solution is very efficient and provides useful physical insight into the various scattering and diffraction processes. It is also universal in nature and can be used to effectively describe the scattered fields from flat, strictly concave or convex, and concave-convex boundaries containing edges. Its accuracy is confirmed via comparison with some reference moment method (MM) results.
Constantinides, Evagoras D.↗
Influence of a fat layer on the near infrared spectra of human muscle: quantitative analysis based on two-layered Monte Carlo simulations and phantom experiments
The influence of fat thickness on the diffuse reflectance spectra of muscle in the near infrared (NIR) region is studied by Monte Carlo simulations of a two-layer structure and with phantom experiments. A polynomial relationship was established between the fat thickness and the detected diffuse reflectance. The influence of a range of optical coefficients (absorption and reduced scattering) for fat and muscle over the known range of human physiological values was also investigated. Subject-to-subject variation in the fat optical coefficients and thickness can be ignored if the fat thickness is less than 5 mm. A method was proposed to correct the fat thickness influence. c2005 Optical Society of America.
NASA Discipline Life Sciences Technologies↗
Characteristics of Coplanar Waveguide on Sapphire for High Temperature Applications (25 to 400 degrees C)
This paper presents the characteristics of coplanar waveguide transmission lines fabricated on R-plane sapphire substrates as a function of temperature across the temperature range of 25 to 400 C. Effective permittivity and attenuation are measured on a high temperature probe station. Two techniques are used to obtain the transmission line characteristics, a Thru-Reflect-Line calibration technique that yields the propagation coefficient and resonant stubs. To a first order fit of the data, the effective permittivity and the attenuation increase linearly with temperature.
Ponchak, George E.↗
Characteristics of Coplanar Waveguide on Sapphire for High Temperature Applications (25 to 400 C)
This paper presents the characteristics of coplanar waveguide transmission lines fabricated on R-plane sapphire substrates as a function of temperature across the temperature range of 25 to 400 C. Effective permittivity and attenuation are measured on a high temperature probe station. Two techniques are used to obtain the transmission line characteristics, a Thru-Reflect-Line calibration technique that yields the propagation coefficient and resonant stubs. To a first order fit of the data, the effective permittivity and the attenuation increase linearly with temperature
Ponchak, George E.↗
Solid-state spectral transmissometer and radiometer
An in situ instrument designed to measure the spectral attenuation coefficient of seawater and the ocean remote-sensing reflectance from 400 to 750 nm is in the test and development stage. It employs a 256 channel, charge-coupled type of linear array measuring the spectral intensities diffracted by a grating. Examples of the types of data delivered by this instrument have been simulated using a breadboard laboratory instrument and an above-water, solid-state radiometer. Algorithms developed using data from these instruments provide measures of chlorophyll a plus phaeophytin a concentrations from less than 0.1 to 77.0 mg/cu m, gelbstoff spectral absorption coefficients, and detrital spectral backscattering coefficients for waters of the west Florida shelf.
Carder, K. L.↗
Investigation of Cloud Interior Structure Using a Tomographic Technique Based on Radon Transform. Application to the Measurements Made by the Research Scanning Polarimeter During CAMP2Ex
The Research Scanning Polarimeter (RSP) is an airborne along-track scanner measuring the polarized and total reflectances in 9 spectral channels. The RSP's uniquely high angular resolution coupled with the high frequency of measurements allows for characterization of liquid-water cloud droplet sizes using the rainbow structure observed in the polarized reflectance measurements. The RSP observations also provide for derivation of 2D field of extinction coefficient inside the cloud using a tomographic technique. This technique utilizes the family of cloud shapes derived using "cutout" technique and corresponding to a number of thresholds in total reflectance (separating bright cloud from its darker background). These shapes can be interpreted as level curves of an abstract "reflectance density", which is then used for derivation of the directional cloud optical thickness (dCOT) tomogram. The latter is a collection of dCOTs parameterized by the angles and offsets of the corresponding view rays (chords) relative to the cloud center. After this, the inverse Radon Transform (the mathematical basis of the X-ray com-puter tomography) is applied to the dCOT tomogram yielding 2D spatial distribution of the extinction coefficient. The later can be converted into droplet number concentration using the droplet size profiles derived from the RSP's polarized reflectance measurements. After tests on synthetic data this technique was applied to real RSP measurements from NASA's Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) conducted in the vicinity of the Philippines during the Southwest Monsoon (August–September 2019). We have investigated the interiors of a number of clouds observed during CAMP2Ex focusing on Cu and CuCg (Tcu) cases. Our retrievals were routinely compared with the correlative measurements by lidar (HSRL-2) and cloud radar (APR-3) that were deployed on the same airborne platform (NASA P-3B) during this field experiment.
Research Scanning Polarimeter↗
A technique for constructing spectral reflectance curves from Viking lander camera multispectral data
A technique for evaluating the construction of spectral reflectance curves from multispectral data obtained with the Viking lander cameras is presented. The multispectral data is limited to 6 channels in the wave-length range 0.4 to 1.1 microns, and several of the channels suffer from appreciable out-of-band response. The technique represents the estimated reflectance curves as a linear combination of known basic functions with coefficients determined to minimize the error in the representation, and it permits all channels, with and without out-of-band response, to contribute equally valid information. The technique is evaluated for known spectral reflectance curves of 8 materials felt likely to be present on the Martian surface. The technique provides an essentially exact fit if the the reflectance curve has no pronounced maxima and minima. Even if the curve has pronounced maxima and minima, the fit is good and reveals the most dominant features. Since only 6 samples are available some short period features are lost. This loss is almost certainly due to undersampling rather than out-of-band channel response.
Park, S. K.↗
LAI inversion from optical reflectance using a neural network trained with a multiple scattering model
The inversion of the leaf area index (LAI) canopy parameter from optical spectral reflectance measurements is obtained using a backpropagation artificial neural network trained using input-output pairs generated by a multiple scattering reflectance model. The problem of LAI estimation over sparse canopies (LAI < 1.0) with varying soil reflectance backgrounds is particularly difficult. Standard multiple regression methods applied to canopies within a single homogeneous soil type yield good results but perform unacceptably when applied across soil boundaries, resulting in absolute percentage errors of >1000 percent for low LAI. Minimization methods applied to merit functions constructed from differences between measured reflectances and predicted reflectances using multiple-scattering models are unacceptably sensitive to a good initial guess for the desired parameter. In contrast, the neural network reported generally yields absolute percentage errors of <30 percent when weighting coefficients trained on one soil type were applied to predicted canopy reflectance at a different soil background.
Smith, James A.↗