Radial velocity and wind measurement with NIMA-NWCA: Comparisons with human estimation and aircraft measurements

The National Center for Atmospheric Research (NCAR) Improved Moments Algori thm (NIMA) calculates the first and second moments (radial velocity and spe ctral width) of wind-profiler Doppler spectra and provides an evaluation of confidence in these calculations. The first moments and their confidences are used by the NCAR Winds And Confidence Algorithm (NWCA), to estimate the horizontal wind. NIMA-NWCA has been used for several years in a real-time application for three wind profilers in Juneau, Alaska. This paper presents results of an effort to evaluate the first moments produced by NIMA and ho rizontal winds produced by NIMA-NWCA through comparison with estimates from "human experts'' and also presents a comparison of NIMA-NWCA winds with in situ aircraft measurements. NIMA uses fuzzy logic to separate the atmosphe ric component of Doppler spectra from ground clutter and other sources of i nterference. The fuzzy logic rules are based on similar features humans con sider when identifying atmospheric and contamination signals in Doppler spe ctra. Furthermore, NIMA attempts to mimic the human experts' assignment of confidence to the moments. A Human Moment Analysis (HMA) tool was developed to assist the human experts in quantifying moments. This tool is described and a methodology of tuning NIMA rules based on human truth specification is presented. NIMA performed well on a dataset specifically chosen to be di fficult. The average absolute error between the HMA estimate and NIMA-deriv ed radial wind estimate was slightly more than 0.3 m s(-1) when data with l ow NIMA confidence were excluded, which is comparable to the Doppler spectr um resolution. The correlation between winds derived from NIMA-NWCA and fro m HMA first-moment estimates exceeded 0.96 when the data with low NWCA conf idence were excluded. The correlation coefficient between NIMA winds and in situ measurements by aircraft was 0.93 when aircraft winds that were belie ved to be accurate were used.