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Distorted antenna surfaces forced to produce a uniform wave front. SUBFORMING employs geometric optics in determining subreflector coordinates to match main reflector surface with known distortions. Antenna with distorted paraboloidal reflecting surface forced to produce uniform wave front by using a Cassegrainian geometry with path-length-compensating subreflector. Program written in FORTRAN V for batch execution.
Wind-tunnel tests to measure unsteady aerodynamic data in the transonic region have been completed on an aspect ratio 2.0 rectangular wing with a supercritical airfoil. The geometric and structural properties of the wing are presented. (Other references contain the measured aerodynamic data.) Both measured and design airfoil coordinates are presented and compared. In addition, measured wing bending and torsional stiffness distributions and some trailing-edge flexibility influence coefficients are presented.
This paper reviews changes in the crystalline structure and geometry of lapped Mn-Zn ferrite heads in sliding contact with magnetic tape and the effects of these changes on magnetic signals. A highly textured, polycrystalline structure was produced on the surface of a single-crystal Mn-Zn ferrite head when it was finished with an aluminum oxide lapping tape. Sliding this lapped surface against a magnetic tape produced a nearly amorphous structure. The sliding process led to a degradation in readback signal of 1 to 2 dB (short-wavelength recording). Furthermore, wear of the magnetic head caused geometrical changes in the head surface. The signal read back with the worn magnetic head was sensitive to operating parameters such as head displacement and tape tension. A change in operating parameters created head-to-tape spacings and, consequently, excessive gains or losses in the readback signal.
The geometric accuracy (GA) and errors in imagery by Landsat-4 and -5 were examined using data from regions with a minimal topography. A least-squares comparison was made between ground truth digitized photographs and TM data for prominent features displayed on a 1:24,000 map. The algorithms used for the transformation of the Landsat data to a Cartesian system are provided. Landsat-5 images had a calculated error of 11.2 m (0.4 pixel) and could not be improved with skew and affine-distortion corrections. However, the digitized images, including road tracks, were considered detailed enough for standard 1:50,000 maps. Landsat-5 imagery, when fully corrected, was consistently superior to Landsat-4 data.
Landsat-4 was launched on July 16, 1982, while the launch of Landsat-5 took place on March 1, 1984. The earth-observing instruments employed were the Multispectral Scanner (MSS), which has flown since 1972 on Landsat satellites, and the Thematic Mapper (TM). The TM provides improved spatial radiance and spectral resolution. The improved capabilities of the TM, the use of different scanning mechanisms relative to the MSS, and the use of a new spacecraft with different mechanical operating characteristics led to a significant challenge in processing the TM and MSS data. The current paper has mainly the objective to present recent results which can provide information regarding the quality of processing as measured against specifications. The results obtained so far for the Thematic Mapper Image Processing System (TIPS), though limited, are found to be quite encouraging as far as the geometric processing of the TM is concerned.
Recent high quality spectral observations have allowed the derivation of constraints on the atmospheric structure of Uranus. The present analysis, which is based on the detailed modeling of a broadband geometric albedo spectrum and high resolution observations of the H2 4-0 quadrupole and 6818.9-A CH4 features, yields (1) a family of models which parameterize an upper tropospheric haze layer, (2) a lower, optically infinite cloud at a given pressure level, (3) the cloud-level methane molar fraction, and (4) the mean ortho/para ratio in the visible atmosphere. The single scattering albedo of atmospheric aerosols exhibits a steep darkening between 5890 and 6040 A.
It is shown that the logical treatment of spinning perfect fluids occurs in a metric-torsion space-time with or without mass conservation. The Lagrangian formulation of a spin density fluid is reviewed, concentrating on the relationship between spin and torsion for metric-torsion space-times. The significance of the mass constraint is discussed, and its consequences for the variation of the Lagrangian is given. That consequence is the geometrization of spin; that is, the Weyssenhoff form relating spin and the trace-free torsion is obtained without any ad hoc assumption.
To characterize and quantify the performance of the Landsat thematic mapper (TM), techniques for dimensionality reduction by linear transformation have been studied and evaluated and the accuracy of the correction of geometric errors in TM images analyzed. Theoretical evaluations and comparisons for existing methods for the design of linear transformation for dimensionality reduction are presented. These methods include the discrete Karhunen Loeve (KL) expansion, Multiple Discriminant Analysis (MDA), Thematic Mapper (TM)-Tasseled Cap Linear Transformation and Singular Value Decomposition (SVD). A unified approach to these design problems is presented in which each method involves optimizing an objective function with respect to the linear transformation matrix. From these studies, four modified methods are proposed. They are referred to as the Space Variant Linear Transformation, the KL Transform-MDA hybrid method, and the First and Second Version of the Weighted MDA method. The modifications involve the assignment of weights to classes to achieve improvements in the class conditional probability of error for classes with high weights. Experimental evaluations of the existing and proposed methods have been performed using the six reflective bands of the TM data. It is shown that in terms of probability of classification error and the percentage of the cumulative eigenvalues, the six reflective bands of the TM data require only a three dimensional feature space. It is shown experimentally as well that for the proposed methods, the classes with high weights have improvements in class conditional probability of error estimates as expected.
A third-order shear deformation theory of laminated composite plates and shells is developed, the Navier solutions are derived, and its finite element models are developed. The theory allows parabolic description of the transverse shear stresses, and therefore the shear correction factors of the usual shear deformation theory are not required in the present theory. The theory also accounts for the von Karman nonlinear strains. Closed-form solutions of the theory for rectangular cross-ply and angle-ply plates and cross-ply shells are developed. The finite element model is based on independent approximations of the displacements and bending moments (i.e., mixed finite element model), and therefore, only C sup o -approximation is required. The finite element model is used to analyze cross-ply and angle-ply laminated plates and shells for bending and natural vibration. Many of the numerical results presented here should serve as references for future investigations. Three major conclusions resulted from the research: First, for thick laminates, shear deformation theories predict deflections, stresses and vibration frequencies significantly different from those predicted by classical theories. Second, even for thin laminates, shear deformation effects are significant in dynamic and geometrically nonlinear analyses. Third, the present third-order theory is more accurate compared to the classical and firt-order theories in predicting static and dynamic response of laminated plates and shells made of high-modulus composite materials.
Various geometric radiating surface (GRS) configurations are evaluated analytically and experimentally for potential use in spacecraft thermal control systems. Egg-crate, honeycomb, flat-parallel, curved-parallel, chevron-shape, and composite fin radiator panel designs were evaluated in terms of mass, apparent emissivity, meteoroid protection, and ease of fabrication; the parallel-finned GRS in composite form was chosen as the most efficient design. The performance of the composite-finned GRS was compared with that of a silver-backed Teflon radiator. The emissivity and dissipative power capabilities of the GRS and radiator are measured. It is observed that the composite-finned GRS has 34 percent less surface area, 34 percent higher heat flux capability, greater meteoroid protection, and 2.8 times higher mass than the Teflon radiator. Future developments and applications for GRCs are discussed.
Geometric correction performance data are presented for the Landsat-5 Thematic Mapper and the Thematic Mapper Image Processing System. Temporal registration and geodetic rectification results are displayed in the form of 90 percent errors. Both error estimation and direct measurements demonstrate that the instrument and system meet performance requirements.
A geometric formulation of Beard's failure detection filter problem is stated using the concepts of (C, A)-invariant and unobservability subspaces. The notions of output separable and mutually detectable families of subspaces introduced by Beard are also clarified. It is shown that mutual detectability is a necessary and sufficient condition for the existence of a detection filter with arbitrarily assignable spectrum. Moreover, it is shown that the failure detection filter problem has a computationally simple solution when the failure events satisfy some mild restrictions. Finally, the complete duality between a generalization of Beard's detection filter problem and the restricted control decoupling problem is illustrated.
Results are reported from large aperture IUE observations of the stratospheres of Uranus and Neptune. The data were collected using 16 Cyg A and B as solar analog stars. The spectra observed were similar to geometric albedos of the predicted in terms of Rayleigh-Raman scattering in the 2200-2800 A region. A falloff was observed near visible wavelengths, a factor which might be attributable to low-altitude haze absorbing in the 3000-4000 A interval. The data also indicated that the Uranus stratosphere does not strongly absorb UV radiation, and is not a good heating source. The stratospheric haze constituents over Uranus could therefore be condensates of CH4 and H2 photochemistry.
A geometric-optical forest canopy model that treats conifers as cones casting shadows on a contrasting background explains the major anisotropies in bidirectional reflectance measurements of a conifer forest canopy. The model uses parallel-ray geometry to describe the illumination and viewing of conifers as three-dimensional cones. Both computer simulation and analytical closed-form expressions are implemented. The results show a good qualitative agreement with the directional reflectance measurements of the conifer stand, indicating that the three-dimensional nature of the canopy is a key factor in determining its directional reflectance.
Techniques are presented and their application illustrated for analysis of remotely sensed data collected with an aircraft carrying a multispectral cloud radiometer and an advanced microwave moisture sounder. The instruments were used on NASA high altitude flights to perform cloud field experiments. Sample IR and microwave brightness temperature data are provided as functions of the ice water path and of the ice water content. Quantitative models are described for deriving the cloud ice (or liquid) water content and the cloud geometric thickness from the radiometric data.
Theoretical models of planetary-atmosphere tidal fields are examined analytically, comparing models based on geometric-height coordinates with those employing log-pressure coordinates. The relationship between the linearized meteorological variables in the two systems is explored for classical tidal theory and its reduction to the Laplace tidal equation, and it is shown that identical horizontal and vertical equations are obtained. Also considered are the tidal zonal-mean bilinear flux convergences and their Eliassen-Palm formulations. Numerical results for problems involving the earth and Mars atmospheres are presented in graphs and discussed.
Two different abrasion formalisms, one based on an energy-independent geometric model and the other based on a quantum-mechanical optical model, are shown to yield comparable fragmentation cross section predictions when used as input to an abrasion-ablation frictional-spectator interaction fragmentation calculation which includes electromagnetic dissociation contributions. The results suggest that any dependence upon the incident ion's kinetic energy above 200 MeV/nucleon is weak. It is also noted that the larger surface diffusiveness of the optical model densities only affects nuclear cross sections for near-projectile-mass fragments, while for heavier nuclei, the sizable cross-section contributions from electromagnetic dissociation negate these differences.
Finite element meshes derived automatically from solid models through recursive spatial subdivision schemes (octrees) can be made to inherit the hierarchical structure and the spatial addressability intrinsic to the underlying grid. These two properties, together with the geometric regularity that can also be built into the mesh, make octree based meshes ideally suited for efficient analysis and self-adaptive remeshing and reanalysis. The element decomposition of the octal cells that intersect the boundary of the domain is discussed. The problem, central to octree based meshing, is solved by combining template mapping and element extraction into a procedure that utilizes both constructive solid geometry and boundary representation techniques. Boundary cells that are not intersected by the edge of the domain boundary are easily mapped to predefined element topology. Cells containing edges (and vertices) are first transformed into a planar polyhedron and then triangulated via element extractor. The modeling environments required for the derivation of planar polyhedra and for element extraction are analyzed.