Vaisala RVP900, User Manual

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• If there is no clutter present, GMAP does little or no filtering.
• GMAP repairs the damage to overlapped (near zero velocity) weather targets.
• The DFT window is determined automatically to be the least aggressive possible to
remove the clutter. This reduces the variance of the moment estimates.
GMAP Model Assumptions
GMAP the following assumptions about the model for clutter, weather, and noise:
• The spectrum width of the weather signal is greater than that of the clutter. This is a
fundamental assumption required for all Doppler clutter filters.
• The Doppler spectrum consists of ground clutter, a single weather target, and noise. Bi-
modal weather targets, aircraft or birds mixed with weather would violate this
assumption.
• The width of the clutter is approximately known. This is determined primarily by the
scan speed and to a lesser extent by the climatology of the local clutter targets. The
assumed width is used to determine how many interior clutter points are removed.
• The shape of the clutter is approximately Gaussian. This shape is used to calculate how
many interior clutter points are removed.
• The shape of the weather is approximately Gaussian. This shape is used to reconstruct
filtered points in overlapped weather.
GMAP Algorithm Steps
The following figure shows the steps used to implement the GMAP approach.
Chapter 7 – Processing Algorithms
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