Furuno GD-280, Руководство оператора

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12-3
12.2.4 Quantization
The entire picture is converted to a digital from called "Quantized Video." A sweep range is
divided into small segments and each range element is "1" if there is radar echo return above a
threshold level, or "0" if there is no return.
The digital radar signal is then analyzed by a ship-sized echo discriminator. As the antenna
scans, if there are five consecutive radar pulses with 1's indicating an echo presence at the exact
same range, a target "start" is initiated. Since receiver noise is random, it is not three-bang
correlated, and it is filtered out and not classified as an echo.
The same is true of radar interference. Electronic circuits track both the closet and most distant
edges of the echo. At the end of the scanning of the echo, the discriminator indicates the
measured maximum range extent and total angular extent subtended by the echo. If the echo is
larger than a ship-sized echo in range extent and/or angular width, adjusted as a function of
range, it is declared to be a coastline and the closest edge is put into the memory as a map of the
area.
This land outline is used to inhibit further acquisition and tracking of ship-sized echoes beyond
the closest coast outline. Five consecutive scans of coastal outline are retained in memory to
allow for signal variation. All smaller echoes are declared to be ship sized and the middle of the
leading edge is used to provide precise range and bearing coordinates of each echo on every
scan. This range/bearing data is matched to previous data and analyzed from scan-to-scan for
consistency. When it is determined to be as consistent as a real target, automatic acquisition
occurs and tracking is initiated.
Continued tracking and subsequent calculation develop the relative course and speed of the
target just as a man would do when plotting the relative course and speed of the target on the
scope with a grease pencil.
The true course and speed of own ship are computed from own ship's gyro and speed inputs,
and the resulting course and speed of each tracked target is easily computed by vector summing
of the relative motion with own ship's course and speed. The resulting true or relative vector is
displayed for each of the tracked targets. This process is updated continually for each target on
every scan of the radar.