Ultra-Wideband Signals for Target Detection in Foliage
Abstract
In this report we have demonstrated the properties of precursor-like waveforms that are important if these waveforms are to be considered for radar detection of targets embedded in foliage. These properties are: (1) Precursor-like waveforms are greatly attenuated in comparison with the excitation signal due to the fact that the precursor formation medium must be highly dispersive and has a rapidly increasing attenuation with frequency. The precursor-like waveforms are formed from sideband energy of the excitation signal in a medium that has greatly attenuated the carrier frequency and upper sideband energy. (2) Precursor-like behavior is exhibited only after propagating through several skin depths of the medium at the carrier frequency of excitation. This insures that the carrier and upper sidebands of the excitation are greatly attenuated. (3) Precursor-like behavior of the response waveform persists with target scattering when the target is embedded in a dispersive. Debye medium. Target scattering attenuates low frequency portions of the spectrum due to Rayleigh scattering from the target at very low frequencies. As long as there remains a substantial portion of the response spectrum that is equalized over a band between the Rayleigh scattering and the carrier frequency, the precursor-like behavior of the time response will be observed. In this case, the duration of the precursors will be increased due to the low frequency bandwidth limitations imposed on the spectrum by the target Rayleigh scattering. (4) Foliage is weakly dispersive when compared to water and results in weak or negligible precursor formation in the coherent or ensemble average waveform at reasonable foliage depths. According to the experimental observations of trees and their wood fibers, as modeled by Brown and Curry, wood conductivity due to the ionic conductivity of salts and minerals in the tree sap dominates Debye losses.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2004
- Accession Number
- ADA432646
Entities
People
- Bertus Weijers
- Elihu J. Tichovolsky
- J. L. Poirier
- John K. Schindler
- Kristopher T. Kim
- Kung-hau Ding
- Leonid I. Perlovsky
Organizations
- Air Force Research Laboratory