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Proceedings with Extended Abstracts (single PDF file) - Radio ...

Proceedings with Extended Abstracts (single PDF file) - Radio ...

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The overall processing flow of the NIMA algorithm is shown in Figure 1. Some of the majorprocessing steps are illustrated in Figures 2-3 using an example spectrum from the northbeam of the Juneau Lemon Creek pro<strong>file</strong>r containing ground clutter, RFI, and point targetcontaminants. Figure 2 shows the averaged spectra both as stacked spectra and as the spectralintensity contour over Doppler velocity (x) and range (y). Median filtering in velocity andrange mitigates the effects of point target contamination and smoothes the spectral surface tofacilitate mathematical analysis.Figure 2. Stacked spectra (left), equivalent spectral intensity contour <strong>with</strong> POP moments (center), and 2dmedian-filtered spectra (right) from Lemon Creek pro<strong>file</strong>r.Spectral intensity scaling is used to emphasize different parts of the spectral surface. Usingrange-normalized scaling of the 2d median filtered values emphasizes the intensity contour inregions of low signal-to-noise (SNR). Mathematical analysis using equation (1) over a smallregion surrounding each point of the resulting spectral surfaces yields information about thelocal curvatures and gradients of the surface.2 2zxy ( , ) = ax ( − x0) + bx ( −x0)( y− y0) + cy ( − y0) + d( x− x0) + ey ( − y0)+ f (1)A number of these derived fields are calculated and membership maps are used to translateeach into a “Doppler Peak membership field.” Fuzzy logic is then used combine these into acombined Doppler Peak membership field. As illustrated in Figure 3, spectral regions <strong>with</strong>high Doppler peak membership values are grouped into “features” that can be classified aspotentially atmospheric, clutter, and/or RFI. The highest scoring atmospheric feature is usedto identify the spectral points from which to calculate the moments.400Figure 3. Combined Doppler Peak membership field (left), resulting Doppler peak features (center), andNIMA moments overlaid on the 1d (velocity) median-filtered spectra used to calculate the moments (right).Confidence in the moments is shown in the side plot.

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