Vaisala IRIS - SHEAR Algorithm

4. In EL Angle, define the elevation angle of data you want to display.
Wind shears associated with gust fronts and microbursts are usually low-level
phenomena, so angles of 1° or less are typically used to detect these.
5. Define Rng / Az Filter.
The first number defines the range length scale for the SHEAR product, in km. This
distance determines the size of the skip that the SHEAR product can tolerate when
dierencing over missing data. It also specifies the length of the radial smoother, which
is applied before the XY smoother.
The second number is the azimuth length scale in degrees.
The skipping and azimuth range length are analogous to the range filter.
6. In Shear Type, select which type of shear you want to compute:
• Radial Shear
The bin-to-bin dierence in the radial velocity.
• Azimuthal Shear
The azimuth-to-azimuth dierence in the radial velocity.
• Elevation Shear
The dierence 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 eects 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.
More information
‣
RHI: Range Height Indicator (page 64)
‣
Display Parameters (page 27)
‣
Product Parameters (page 23)
‣
Associating Products with Tasks (page 17)
5.6.1
SHEAR Algorithm
The SHEAR algorithm shown in the following figure is for radial shear. The azimuth shear is
similar in "B-scan" space (range-azimuth).
Chapter 5 – Configuring and Scheduling Optional IRIS Products
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