Deconvolution of target signature for a scene with bistatic impulse radiating antennas and a sphere
A model for an impulse radiating antenna (IRA) has been developed in WIPL-D. A scene using a bistatic pair of these IRAs is modeled with a sphere target and is simulated in the frequency domain. The input to the antenna is a Gaussian pulse, and the current on the receive antenna is plotted vs. frequency. This receiver response is proportional to the scattered field from the sphere. The frequency domain data are processed to give the time domain response. The objective of this work is to deconvolve the signature of the scatterer from the receiver transient response. Additional separate simulations for each scene component and electromagnetic interaction were needed and were performed using WIPL-D. The process is successful for this scene, which does not include a ground plane. The analysis of the simulated data and deconvolution of the target signature are done in Matlab.
Analysis of the impulse radiating antenna
A procedure is developed for analyzing the radiation on the impulse radiating antenna. High- and low-frequency asymptotes for the radiation on axis are developed, and comparison to a wire-grid model run under the Nuclear Electromagnetics Code is favorable. These preliminary results indicate no late-timing ringing of the radiated waveform.<<ETX>>
The Earth's Angular Momentum Budget on Subseasonal Time Scales
Irregular length of day (LOD) fluctuations on time scales of less than a few years are largely produced by atmospheric torques on the underlying planet. Significant coherence is found between the respective time series of LOD and atmospheric angular momentum (AAM) determinations at periods down to 8 days, with lack of coherence at shorter periods caused by the declining signal-to-measurement noise ratios of both data types. Refinements to the currently accepted model of tidal Earth rotation variations are required, incorporating in particular the nonequilibrium effect of the oceans. The remaining discrepancies between LOD and AAM in the 100- to 10-day period range may be due to either a common error in the AAM data sets from different meteorological centers, or another component of the angular momentum budget.