7. If it is determined that false alarms are occurring, there are several approaches you can
take to balance sensitivity against false alarm rate.
In tuning your system to reduce false alarms, it is important to make gradual changes
and evaluate them on test cases that you have recorded. Some examples of actions that
you can take to reduce false alarms are as follows (note the reverse of each example
can be used to increase sensitivity):
• Gradually increase the range filter in the SHEAR Product Configuration menu from 1
to 2 km (0.6 to 1.2 mi).
• Increase the SHEAR magnitude threshold in the WARN Product Configuration
menu.
• Increase the threshold AREA size in the WARN Product Configuration menu up to
2 km (1.2 mi).
• Require that 2 low-level scans from the same task both detect the SHEAR in the
WARN product: a two-look test.
• Add a warning criterion that requires reflectivity aloft. This can be based on a dBZ
PPI at a higher angle.
Make sure dry microbursts are not common in your area. If they are, you may need to
use a VIL criterion and employ more elevation angles in your associated task.
Chapter 5 – Configuring and Scheduling Optional IRIS Products
RESTRICTED 187
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