Vaisala IRIS, User Manual

Page: 35 / 394

Because of earth curvature, ground clutter and beam blockage, radars are poor at looking
for features close to the surface.
This means that the
BASE product cannot detect echo bases to very low levels.
When precipitation in excess of the specified dBZ contour is reaching the ground, or near
to reaching the ground, the
BASE product displays a special color to indicate that there is
a BASE , but its height cannot be determined.
1. Select Type > BASE .
2. Configure the BASE product:
Data:Display
Choose from
dBT Height
,
dBZ Height
, or
dBZc Height
Max Range
Select the maximum range for the product. Recall that earth curvature effects are
greater at greater ranges.
You can display a PPI at your lowest elevation angle and use the cursor tool to
see what heights are possible to observe at various ranges.
For example, for a 0.5° elevation angle at 100 km (62.1 mi), the beam is centered
at 2.3 km (1.4 mi). It is not possible to detect echo bases lower than this.
dBZ Contour
Select the dBZ threshold for the echo base.
3. Apply the AZ/EL Smoother .
Enter the values in degrees, first for the azimuth and then for the elevation direction.
Typical values are 1.0, 1.0.
More information
‣
Display Parameters (page 27)
‣ Product Parameters (page 23)
‣
Associating Products with Tasks (page 17)
‣
TOPS: Echo Tops (page 86)
Chapter 3 – Configuring IRIS Products
RESTRICTED 33