Vaisala IRIS, User Manual

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2. Configure the TOPS product:
Data : Display
• Z Height
•
T
Height
The product can bederived from either Z or T data. If Z is selected as the
Product Data parameter, but at run time only T is available (or vice versa), the
product runs with the available data parameter.
dBZ Contour
You can select the threshold contour level in dBZ. The TOPS algorithm then
makes a downward search at constant range in cylindrical coordinates to
determine when the threshold is crossed. It then interpolates in height to obtain
the height of the threshold contour. Similar to the
CAPPI , there must be an
elevation tilt both above and below the contour to obtain a valid top height.
3. When the downward search detects a dBZ value greater than the threshold, there are
the following cases:
Normal Case
The dBZ value in the next higher ray (elevation angle) at the same surface range
is used to interpolate the height of the contour that must lie in between.
Undetected Echo Aloft
If there is no detectable echo in the next higher ray aloft, then an interpolation
cannot be done. However, a top must exist somewhere between these 2 rays. In
this case, the top height is taken as the height of the point where the detection of
dBZ >> Threshold was made.
No Ray Aloft
If there is no higher elevation angle aloft, then a top exists somewhere aloft, but
there is no information as to how much higher the top may be. In this case a
special color (indicated by "
??? " in the legend) denotes that an indeterminate top
exists.
For example, at ranges less than 5 km (3.1 mi) in the volume scan shown in the
following figure, the algorithm cannot determine tops that are above the highest
elevation angle.
0
5
10
10 20 30 40 50
44.9
34.9 26.5
18.3 13.9
11.1 9.3
7.4
6.4
5.5
4.6
3.6
2.7
1.7
0.8
Figure 29 Example of 15-tilt Volume Scan
Chapter 3 – Configuring IRIS Products
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