Space-time processing for suppression of bottom reverberation
The major problem for sonars operating in shallow water is the detection of low Doppler targets in the presence of severe bottom reverberation. For a modern sonar with an azimuthally omni-directional transmitter; the Doppler of bottom reverberation is proportional to /spl nu/cos /spl theta/ where /spl nu/ is the speed of the sonar platform and /spl theta/ is measured from the bow or heading direction. For a towed array receiver, reverberation of various Doppler arriving on sidelobes limits the effectiveness of advanced waveforms. This smearing of sidelobe reverberation over a Doppler range of /spl plusmn//spl nu/ makes it difficult to detect targets with speeds less than that of the sonar platform. Standard adaptive beamforming algorithms are ineffective due to the conflict between desire for narrow frequency bins for good Doppler confinement and wide frequency bins for rapid convergence. We present space-time processing algorithms that overcome these difficulties and permit the detection of low Doppler targets from moving platforms.
Geometric comb waveforms for reverberation suppression
The major problem for sonar systems operating in shallow water is reverberation from the ocean bottom. A new class of waveforms is described which combines high range resolution with excellent Doppler properties for detecting moving targets in stationary reverberation. The waveforms consist of multiple simultaneously transmitted CW tone pulses. The tones are non-uniformly spaced in frequency to break up range ambiguities. A special subclass is the geometric comb in which the frequency spacing between the adjacent components follows a geometric progression. Analytic approximations can be used to obtain the important properties of this class, resulting in a practical design methodology. The resulting waveforms have excellent Doppler properties and an unambiguous high resolution range estimation capability. Techniques for reducing the peak-to-average power ratio are discussed.<<ETX>>
A slowly rotating coil system for AC field measurements of Fermilab Booster correctors
A method for measurement of rapidly changing magnetic fields has been developed and applied to the testing of new room temperature corrector packages designed for the Fermilab Booster Synchrotron. The method is based on fast digitization of a slowly rotating tangential coil probe, with analysis combining the measured coil voltages across a set of successive magnet current cycles. This paper presents results on the field quality measured for the normal and skew dipole, quadrupole, and sextupole elements in several of these corrector packages.