Wind Measurement by Conventional Radar with a Dual Beam pattern

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  • a Air Force Cambridge Research Laboratories, Sudbury, Mass.
  • | b ARACON Geophysics Company, Inc., Concord, Mass.
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Abstract

A method of measuring wind velocities by a dual beam modification to conventional (non-Doppler) radars is described. The two beams are disposed slightly to either side of the antenna bore-sight axis. This results in a double-peaked Doppler velocity (frequency) spectrum which is centered on the radial velocity component and whose peaks are spaced proportionally to the transverse velocity component. Such a dual beam Doppler radar is therefore able to measure the complete vector velocity. But the conventional radar can measure only the echo fluctuation spectrum. For any Doppler spectrum, there is a unique fluctuation spectrum, and in the case of the double peaked Doppler spectrum, the fluctuation spectrum has a secondary peak at a frequency corresponding to the peak spacing. Thus, the conventional radar can also measure the transverse velocity component. While spectrum contamination by turbulence and wind shear may cause the peaks to blend with one another, it is shown that the variance of the fluctuation spectrum for the dual beam mode minus that of the single beam is nevertheless uniquely related to transverse target velocity. Various applications to meteorology are described. The techniques are also directly applicable to the measurement of aircraft ground velocity using airborne radars.

Abstract

A method of measuring wind velocities by a dual beam modification to conventional (non-Doppler) radars is described. The two beams are disposed slightly to either side of the antenna bore-sight axis. This results in a double-peaked Doppler velocity (frequency) spectrum which is centered on the radial velocity component and whose peaks are spaced proportionally to the transverse velocity component. Such a dual beam Doppler radar is therefore able to measure the complete vector velocity. But the conventional radar can measure only the echo fluctuation spectrum. For any Doppler spectrum, there is a unique fluctuation spectrum, and in the case of the double peaked Doppler spectrum, the fluctuation spectrum has a secondary peak at a frequency corresponding to the peak spacing. Thus, the conventional radar can also measure the transverse velocity component. While spectrum contamination by turbulence and wind shear may cause the peaks to blend with one another, it is shown that the variance of the fluctuation spectrum for the dual beam mode minus that of the single beam is nevertheless uniquely related to transverse target velocity. Various applications to meteorology are described. The techniques are also directly applicable to the measurement of aircraft ground velocity using airborne radars.

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