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3. If needed, construct a volume scan.
Some products require volume scan tasks, either PPI Full or PPI Sector scans taken at
multiple elevation angles. Volume scan products include:
• BEAM
• CAPPI
• MAX
• TOPS
• VIL
• XSECT
• VVP
• WIND
For these products, multiple elevation angles are required in the associated task. There
is a tradeoff between the number of elevation angles, the quality of the product and the
task scan time. More elevation angles produce higher quality products at the expense
of taking more time to complete the volume scan.
A typical volume scan is shown in the following figure. In this example, the height
resolution is 1 km (0.6 mi) at 60 km (37.3 mi) range, for heights less than 10 km (6.2 mi).
A 1° beam is 1 km (0.6 mi) wide at 60 km (37.3 mi), so this scheme matches the antenna
resolution. If close range work is important, you must add higher elevation angles to
cover the upper regions.
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 1 Example of 15-tilt Volume Scan
When constructing a volume scan task configuration, it is a good idea to do a drawing
such as the one in the example, with a 1:1 vertical:horizontal scale so that you get a true
picture of the sampling geometry.
The example is corrected for earth curvature, as are all IRIS products.
Also, because of beam widening effects, the accuracy of all products degrades with
range. For example, the beam width at 120 km (74.6 mi) range is 2 km (1.2 mi) across
for an antenna with a 1° beam. This is a fundamental limitation of radar sampling.
3.2.2 Configuring Map Projections
Chapter 3 – Configuring IRIS Products
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