USER’S MANUAL__________________________________________________________________
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power is also calculated (T0). The autocorrelations are sent to the range
averaging and moment extraction steps.
2.9.3 RVP900 DFT/FFT Processing
The DFT/FFT mode allows clutter cancelation to be performed in the
frequency domain. DFT is used in general, with FFTs used if the requested
sample size is a power of two.
Three standard windows are supported to provide the best match of
window width to the spectrum dynamic range:
- Rectangular
-Hamming
- Blackman
- Exact Blackman
- Von Han
After the FFT step, clutter cancelation is done with the options of using
GMAP, a selectable fixed width filter that interpolates across the noise or
any overlapped weather, or an adaptive filter which automatically
determines the optimal width. This technique preserves overlapped
weather as compared to time domain notch filters, which always attenuate
overlapped weather to some extent, depending on the spectrum width.
After clutter cancelation, R0, R1, and R2 are computed by inverse
transform and these are used for moment estimation.
2.9.4 Random Phase Processing for
Second Trip Echo
Second trip echoes can be a serious problem for applications that require
operation at a high PRF. Second trip echoes can appear separately, or can
be overlaid on first trip echoes (second trip obscuration). The random
phase technique
3
separates the first and second trip echoes so that:
- In nearly all cases, the second trip echo can be removed from the first
trip, even in the case of overlapped first and second trip echoes. The
benefit is a clean first trip display.
- The second trip echoes can be recovered and placed at their proper
range at first trip/second trip signal ratios of up to 40 dB difference for
overlapped echoes. Because of the WDR of weather echoes, this
power limit is sometimes exceeded.
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