32nd Conference on Broadcast Meteorology/31st Conference on Radar Meteorology/Fifth Conference on Coastal Atmospheric and Oceanic Prediction and Processes

Sunday, 10 August 2003: 5:15 PM
Single antenna interferometry to measure wind
Guifu Zhang, NCAR/RAP, Boulder, CO; and R. J. Doviak, J. Vivekanandan, and T. Y. Yu
Poster PDF (257.9 kB)
Wind velocity can be measured by the Doppler method, interferometry technique and tracking reflectivity echoes by correlation (TREC). The Doppler method is routinely used to measure radial velocity. The Doppler method uses the phase of auto-correlation function of received signal to estimate radial wind, which is prone to aliasing. The interferometry technique with a spaced antenna (SA) radar system has advantages in obtaining transverse velocity with fine resolution, and has been successfully used to measure transverse wind. Both the Doppler method and the interferometry technique directly measure wind (velocity of randomly distributed scatterers), and they are able to determine wind even if the target medium is statistically homogenous. The TREC method tracks individual features in radar reflectivity to determine the feature motions. However, when reflectivity is not conserved, reflectivity motion is not same as the wind velocity and also the TREC method does not work when the reflectivity field is homogenous.

The interferometry technique uses the magnitude of cross-correlation function and the problem of phase aliasing is not involved. The problem of using interferometry technique for wind measurement is that it has been largely dependent on a spaced antenna (SA) radar system, in which scattered signals are received at different receivers and are correlated to estimate the transverse wind. Also, a large beam width is required to have accurate wind measurement for a turbulent medium. To our knowledge, however, the interferometry technique with a single-aperture radar has not been investigated.

In this paper, we propose single antenna interferometry technique to measure wind and study the feasibility in practical applications. We propose Angular Interferometry (AI) technique to determine transverse wind and Range Interferometry (RI) technique to measure radial wind. The radial wind velocity is estimated from the ratio of the range cross-correlation magnitudes at positive and negative lags, and transverse wind is obtained from that of angular correlation magnitudes. It is noted that neither the AI nor RI technique is a TREC method as both AI and RI are applicable even if the reflectivity field is homogeneous. The feasibility of the method is studied through error analysis of wind estimates. The standard deviations of the estimated wind velocities are derived, and their sensitivity to resolution, sample time, and turbulence are analyzed. It shows that the AI technique needs small beam size to measure wind accurately, opposite to the SA technique, while RI technique requires fine range resolution to perform well.

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