Vaisala IRIS, User Manual

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6. In Shear Type , select which type of shear you want to compute:
• Radial Shear
The bin-to-bin difference in the radial velocity.
• Azimuthal Shear
The azimuth-to-azimuth difference in the radial velocity.
• Elevation Shear
The difference between the radial velocity at the selected and next higher elevation
angle. Requires a volume scan.
• Combined Shears
The RMS value of the radial, azimuth, and/or elevation shear. This is sometimes
referred to as the total shear.
7. In VVP , select the name of a VVP product.
The wind speed and direction from the nearest VVP wind product of this name is used
to remove the effects of the mean wind on the azimuth shear calculation.
This
VVP product must be scheduled to run. Use of the azimuth or combined shear is
not recommended without this correction.
8. In VVP Age , specify the maximum number of minutes between the data for the VVP
product and the data for this product.
This prevents old
VVP winds from being misapplied. If a VVP product is not found in
this time window, the mean wind correction is not applied when computing the
azimuth shear.
9. Define SLINE settings:
Count and Time
Enter the number of forecast points and the time interval between each forecast
point and select
Ok .
The time you specify is inserted in the field.
Max Time Step
The forecast of shear line motion uses the previous shear line product.
Max Time Step specifies how far back in time the previous SLINE product can be.
If none exists in this time frame, no forecast is made.
Max Velocity
Enter the maximum expected velocity. If the computed velocity exceeds this
value, the shear line is considered to be a new feature, and no forecast is made.
Shear Threshold
Enter the minimum speed difference per km that must be present to indicate a
shear line. Winds that do not meet this speed are ignored.
Threshold Area
Enter the minimum size of the wind shear area in square km that must be present
to indicate a shear line. Wind shear areas below this threshold are ignored.
RMS Fit Tolerance
Enter the standard deviation allowed when fitting the shear line. The line is
discarded if the points do not fit within this tolerance, indicating a random
scattering of points and not a shear line.
Minimum Sline Length
Enter the minimum length distance in km used to estimate a shear line. Shear
lines that are below this length are ignored.
IRIS Product and Display User Guide M211319EN-H
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