Showing papers by "James D. Iversen published in 1988"
TL;DR: In this article, the authors used calibrated L(HH), C(HH) and Ku(VV) radar data to derive characteristic backscatter coefficients sigma(0) for three lava flow units, an alluvial fan, and a playa surface.
Abstract: The ability of the wind to move particles and the flux of windblown sand are both dependent on the topographic roughness of the surface, as measured by the aerodynamic roughness, z(0). For most surfaces, topographic roughness controls many of the characteristics of the radar return, and the magnitude of the radar backscatter can be regarded as a measure of the surface roughness at or near the wavelength scale. Radar backscatter data may therefore be useful in obtaining a value of aerodynamic roughness which can be used to assess aeolian sediment transport via remote sensing. In this study, calibrated L(HH), C(HH) and Ku(VV) radar data were used to derive characteristic backscatter coefficients sigma(0) for three lava flow units, an alluvial fan, and a playa surface. Preliminary analyses show that values of sigma(0) and z(0) both increase with topographic roughness and that there is a good correlation between the two coefficients. This correlation suggests that it may be possible to assess aerodynamic roughness directly from radar data.
25 citations
01 Jan 1988
TL;DR: In this article, the Navier-Stokes equations are solved to steady state for a finite-length, physically realistic model using an alternating-direction implicit scheme that is formally second order accurate in space and first-order accurate in time The equations are linearized and uncoupled by evaluating variable coefficients at the previous time iteration.
Abstract: The azimuthal-invariant, three-dimensional cylindrical, incompressible Navier-Stokes equations are solved to steady state for a finite-length, physically realistic model The numerical method relies on an alternating-direction implicit scheme that is formally second-order accurate in space and first-order accurate in time The equations are linearized and uncoupled by evaluating variable coefficients at the previous time iteration Wall grid clustering is provided by a Roberts transformation in radial and axial directions A vorticity-velocity formulation is found to be preferable to a vorticity-streamfunction approach Subject to no-slip, Dirichlet boundary conditions, except for the inner cylinder rotation velocity (impulsive start-up) and zero-flow initial conditions, nonturbulent solutions are obtained for sub- and supercritical Reynolds numbers of 100 to 400 for a finite geometry where R(outer)/R(inner) = 15, H/R(inner) = 073, and H/Delta-R = 15 An axially-stretched model solution is shown to asymptotically approach the one-dimensional analytic Couette solution at the cylinder midheight Flowfield change from laminar to Taylor-vortex flow is discussed as a function of Reynolds number Three-dimensional velocities, vorticity, and streamfunction are presented via two-dimensional graphs and three-dimensional surface and contour plots
1 citations