Weather radar signal processing techniques

Improvements to the Spectrum Width Estimator for the NEXRAD Network

In 2005 , 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. The goal of this project is to recommend a spectrum width estimator for the ORDA that is equivalent to the legacy estimator.

Theoretical, simulation, and data analyses showed that the ORDA spectrum width estimator on non-windowed 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.

More details about this issue can be found on my 2007 AMS Radar Conference paper.

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