Doppler Weather Radar Research and Development
NSSL Project 7 – Investigation of Advancements in Radar Technology toward the Improvement of Hazardous Weather Detection and Warnings:
Open Radar Data Acquisition (ORDA) Spectrum Width Estimation
Funding Type: CIMMS Task II
Objectives
Recommend a spectrum width estimator for the ORDA that is equivalent to
the legacy estimator.
Accomplishments
Recently, the NEXRAD network was upgraded with the Open Radar Data Acquisition
(ORDA) subsystem, which includes new receivers, signal processors,
and control subsystems. Before this upgrade, the legacy RDA estimated
the spectrum width using the standard pulse-pair technique. The new
signal processor implements a similar spectrum width estimator, but
relies on a Discrete Fourier Transform (DFT)-based estimator to compute
the first few lags of the time-series autocorrelation function. In
general, the new and legacy autocorrelation estimators are not equivalent,
resulting in inconsistent spectrum width estimates.
Theoretical, simulation, and data analyses showed that the ORDA spectrum width estimator on nonwindowed data is positively biased, especially for narrow spectrum widths. Given that biased estimates would negatively impact the performance of algorithms that rely on the spectrum width (e.g., the radar echo classifier, or the new turbulence detection algorithm), we proposed changes to the new spectrum width estimator to make it unbiased, mathematically equivalent to the pulse-pair implementation, and naturally able to handle data window effects. These changes were approved for operational implementation by the NEXRAD Technical Advisory Committee and are currently underway.
This project has been completed.
Publications
Torres, S. M., C. D. Curtis, D. S. Zrnic, and M. Jain, 2007: Analysis of
the new NEXRAD spectrum width estimator. Preprints, 33rd
International Conf. on Radar Meteorology, Cairns, Australia. Amer. Meteor. Soc., P7.8.
Spectrum width fields from ORDA computed from the same time-series data using a rectangular data window (left) and a Hamming data window (right). Apparent differences in these fields are a consequence of the biased nature of the ORDA autocorrelation estimator.