Tong Gan

Error estimation of spectral parameters for high‐resolution wind and turbulence measurements by wind profiler radars

Using numerical simulations, we investigated a method for calculating the spectral parameters from Doppler spectra collected by high-resolution wind profiler radars (WPRs). Because high-resolution WPRs collect a huge amount of Doppler spectra, calculations must be simple and fast. The proposed method has two steps. In the first step, the echo range (Recho), in which the Doppler spectrum point with peak intensity is contained and all the smoothed Doppler spectrum points have intensities that are greater than the noise intensity, was determined. For producing the smoothed Doppler spectrum, a running average with equal weight (RA) or multitaper method (MTM) was used. In the second step, the spectral parameters were calculated using the Doppler spectrum points within Recho. By comparing the performance of the computation methods using RA and MTM, we concluded that the computation method using RA is more suitable because it has better estimation performance for small spectrum widths and the calculations are faster. Estimation error of the spectral parameters depends on the determination accuracy of the Doppler spectrum peak and Recho. Furthermore, for the case of a 512-point Doppler spectrum and 13-point RA, the estimation errors tend to be independent of the signal-to-noise ratio (SNR) when the peak level of the Doppler spectrum (pest) is ∼8 dB or more greater than the noise intensity. For pest of <∼8 dB, the estimation errors are well correlated to pest and the SNR. Therefore, the number of incoherent integration times should be determined by considering the SNR and pest.

Spectral parameters estimation in precipitation for 50 MHz band atmospheric radars

Fifty megahertz band atmospheric radars (ARs) can detect clear air echoes and hydrometeor echoes simultaneously. However, in order to calculate spectral parameters (i.e., echo power, Doppler velocity, and spectrum width) of the clear air echo accurately, the clear air echo must be separated from the hydrometeor echo well. In this study, we propose methods (top method and two-echo method) for calculating the spectral parameters in precipitation region. The top method is used when raindrops or solid hydrometeors with small echo intensities exist. The top method sets an echo cut level by using the peak intensity of the clear air echo. The echo cut level is used for separating clear air echoes from hydrometeor echoes. The two-echo method is used when solid hydrometeors with large echo intensities exist. The two-echo method sets the echo cut level by using the local minimum of echo intensity between the clear air echo and the hydrometeor echo. Measurement results obtained by the vertical beam of the middle and upper atmosphere radar during a precipitation event on 26 October 2009 were used for evaluating the performance of the top and two-echo methods. The echo cut levels of the top and two-echo methods were determined from numerical simulation. The measurement results demonstrate that the top and two-echo methods are useful for reducing errors of spectral parameters.