Large-scale anisotropy in stably stratified rotating flows

We present results from direct numerical simulations of the Boussinesq equations in the presence of rotation and/or stratification, both in the vertical direction. The runs are forced isotropically and randomly at small scales and have spatial resolutions of up to $1024^3$ grid points and Reynolds numbers of $\approx 1000$. We first show that solutions with negative energy flux and inverse cascades develop in rotating turbulence, whether or not stratification is present. However, the purely stratified case is characterized instead by an early-time, highly anisotropic transfer to large scales with almost zero net isotropic energy flux. This is consistent with previous studies that observed the development of vertically sheared horizontal winds, although only at substantially later times. However, and unlike previous works, when sufficient scale separation is allowed between the forcing scale and the domain size, the total energy displays a perpendicular (horizontal) spectrum with power law behavior compatible with $\sim k_\perp^{-5/3}$, including in the absence of rotation. In this latter purely stratified case, such a spectrum is the result of a direct cascade of the energy contained in the large-scale horizontal wind, as is evidenced by a strong positive flux of energy in the parallel direction at all scales including the largest resolved scales

Advanced Meteorological Temperature Sounder (AMTS) simulations

Simulation studies are reported on temperature retrievals from AMTS and their effect on atmospheric analysis. Observations are simulated from radiosonde reports and observed cloud cover. Temperature retrievals are performed and RMS temperature and thickness errors are calculated relative to the radiosonde profiles and compared to similarly generated HIRS statistics. Significant improvement over HIRS is found throughout the atmosphere but especially in the stratosphere and lower troposphere

A hybrid MPI-OpenMP scheme for scalable parallel pseudospectral computations for fluid turbulence

A hybrid scheme that utilizes MPI for distributed memory parallelism and OpenMP for shared memory parallelism is presented. The work is motivated by the desire to achieve exceptionally high Reynolds numbers in pseudospectral computations of fluid turbulence on emerging petascale, high core-count, massively parallel processing systems. The hybrid implementation derives from and augments a well-tested scalable MPI-parallelized pseudospectral code. The hybrid paradigm leads to a new picture for the domain decomposition of the pseudospectral grids, which is helpful in understanding, among other things, the 3D transpose of the global data that is necessary for the parallel fast Fourier transforms that are the central component of the numerical discretizations. Details of the hybrid implementation are provided, and performance tests illustrate the utility of the method. It is shown that the hybrid scheme achieves near ideal scalability up to ~20000 compute cores with a maximum mean efficiency of 83%. Data are presented that demonstrate how to choose the optimal number of MPI processes and OpenMP threads in order to optimize code performance on two different platforms.Comment: Submitted to Parallel Computin

Anti-jamming techniques for multichannel SAR imaging

An airborne broadband jammer present in the mainbeam of a Synthetic Aperture Radar (SAR) can potentially destroy a large region of the SAR image. In addition to this, multipath reflections from the ground, known as hotclutter or terrain scattered interference will add a non-stationary interference component to the image. The goal of interference suppression for SAR is to successfully suppress these interferences while not significantly effecting the image quality by blurring, reducing the resolution or raising the sidelobe level. This paper provides an analysis of the degradation from hot-clutter, the limited restoration that slow-time Space Time Adaptive Processing (STAP) can provide and how fast-time STAP can improve the final image.Luke Rosenberg and Doug Gra

Fast-time filtering with multichannel SAR

Large regions of a Synthetic Aperture Radar (SAR) image can potentially be destroyed by an airborne broadband jammer. Jammer components include both the direct-path and multipath reflections from the ground, known as hotclutter or terrain scattered interference. Using multiple antennas on a SAR provides spatial degrees of freedomand allows for beamforming to reject the direct-path signal. However, to effectively suppress non-stationary hot-clutter components, fast-time taps fromwithin a pulse have shown to be effective for airborne radar, [1]-[2]. The goal of interference suppression for SAR is to successfully suppress these interferences while not significantly effecting the image quality by blurring, reducing the resolution or raising the side-lobe level. This paper looks at two fast-time STAP algorithms, the Minimum Variance Distortionless Response (MVDR) and the Generalised Sidelobe Canceller (GSC) to study the effect of non-stationary interference suppression for SAR images.Luke Rosenberg and Doug Gra

Robust interference suppression for multichannel SAR

Forming a Synthetic Aperture Radar (SAR) image while suppressing a broadband jammer can potentially destroy large regions of the image. In addition to this, multipath reflections from the ground, known as hot-clutter or terrain scattered interference will add a non-stationary interference component to the image. The goal of interference suppression for SAR is to successfully suppress these interferences while not significantly effecting the image quality by blurring, reducing the resolution or raising the side-lobe level. Using multiple antennas on a SAR provides spatial degrees of freedom and allows for adaptive beamforming to suppress the jammer signals. This paper presents two constrained spatial techniques which reduce the interference level without significantly effecting the image quality

Reduced rank interference suppression for multichannel SAR

Large regions of a Synthetic Aperture Radar (SAR) image can potentially be destroyed by an airborne broadband jammer. Jammer components include both the direct-path and multipath reflections from the ground, known as hot-clutter (HC) or terrain scattered interference. Using multiple antennas on a SAR provides spatial degrees of freedom and allows for beamforming to reject the direct-path signal. Previous studies have shown that derivative constraints when combined with fast-time taps can suppress HC while maintaining a reasonable SAR image. This approach however requires an expensive matrix inverse and may not be implementable in real time. This paper therefore presents a fast-time Space Time Adaptive Processing (STAP) algorithm with a reduced rank constrained Generalised Sidelobe Canceller (GSC).Luke Rosenberg, Doug Grayhttp://www.dlr.de/hr/Portaldata/32/Resources/dokumente/eusar/EUSAR2006-Final-Conference-Program-2006-May-05.pd

Investigation of sputtering effects on the moon's surface Eleventh quarterly status report, 25 Oct. 1965 - 24 Jan. 1966

Implications of Lunar 9 moon probe, sputtering yield reduction due to surface roughness, water formation by solar wind bombardment, photometric function of moon, and chemical sputterin

Fast-time STAP performance in pre and post range processing adaption as applied to multichannel SAR

Hot-clutter cancellation using fast-time Space Time Adaptive Processing (STAP) can occur either pre or post range processing (RP) and to date, there has not been a direct comparison on which method offers the best results. This paper provides an analytic comparison which is verified with simulation and aims to provide insight into the location of the adaptive filter which would provide the best hot-clutter suppression. The covariance models are tested with signal models used in a multichannel Synthetic Aperture Radar (SAR)

Different homogeneity detectors for improving space-time adaptive radar performance in heterogeneous clutter

© Copyright 2006 IEEESecondary data selection for estimation of the clutter covariance matrix in space-time adaptive processing (STAP) is normally obtained from cells (range rings) in close proximity of the cell under test. The aim of this paper is the analysis of performance improvement of Space-Time Adaptive radars when secondary data selection is obtained by discriminating between quasi-homogeneous areas on the ground which generate clutter with different statistics (i.e. clutter edges including littoral, farmland-wooded hills or rural-urban interfaces). The algorithm presented in this paper, referred to as the Different Homogeneity Detector (DHD), has been tested with simulated data obtained by using a general clutter model and a uniform linear array.Massimo Bertacca, Douglas A. Gray, Luke Rosenber