Rapid-Scanning Measurements of Wind-Produced Doppler on an Asymmetrical Microwave Transhorizon Propagation Path

摘要

Conventional methods for monitoring winds aloft have inherent spatial and/or temporal limitations that severely restrict their usefulness. An alternate solution is the use of transhorizon bistatic radio techniques. By using a phase-coherent system with some form of beam-swinging capability, it is possible to measure the wind-produced Doppler shifts associated with moving off-path scatterers. In this experiment a rapid data-gathering system is used to remotely probe the wind-field velocity structure in the common volume region of a 164-km transhorizon propagation path. The phase-stable system operates at 3.2 GHz and employs a 12-element horizontal receiving antenna array. The amplitudes and relative phases of the output signals from the individual elements are sequentially sampled and recorded at a 40-Hz rate. Off-line processing of the amplitude and phase data samples is used to 'scan' in azimuth a 0.3 deg wide fan beam through a 3.88 deg sector and to obtain virtual simultaneous Doppler spectra measurements at a continuum of angles within the sector scanned. An algorithm developed to identify the apparent source direction of each spectral component permits an appropriate weighting to be applied to the spectra on the basis of angle-of-arrival. The average Doppler shift (spectrum centroid) as a function of the array pointing angle is interpreted in terms of the average transverse wind speed and direction.