Figure 6 FCAST Example Configuration
1. Select Type > FCAST.
2. In Type, select the input product type and name.
Select a product that can produce a reasonable echo motion.
If you are using the product to forecast the motion of a VIL features, base the forecast
on a VIL product.
In the example, a CAPPI product of dBZ is selected.
3. Specify the Threshold Level.
The algorithm applies a weighting function to the data based on this level. Values
above this level are amplified and values below this level are suppressed by the
weighting function.
When you choose the level, look at a display in loop mode and get a feeling for what
color boundary moves in a representative way.
Usually you want to select a weak value to make sure it is always present when there
are echoes. In the example, 30 dBZ is selected.
4. Specify the Correlation threshold.
The correlation algorithm returns a speed, direction and a correlation value which
serves as a quality indicator.
The value that you enter here is used as a threshold. If the calculated correlation value
in the product is larger than the threshold that you set, a forecast product is generated.
Otherwise no forecast product is generated.
The example requires a correlation of 50 %. A larger value would be more restrictive. A
smaller value is more likely to pass unreliable motion estimates when the data are noisy.
5. Specify Max Velocity in km/hr.
It is also possible that the forecast product has a suciently high correlation, but makes
an absurd velocity perhaps because of random noise.
To prevent this, enter the maximum velocity that you would expect to see for weather
echoes in your area. A value of 120 km/hr (74.6 mi/hr) is a reasonable first guess.
IRIS Product and Display User Guide M211319EN-H
38 RESTRICTED
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