Antenna and Radar Control

Scan Mode

Use Scan Mode to select the following modes.

Azimuth and Elevation for PPI and RHI Scans

For PPI Sector and RHI scans, you must specify start and stop limits for the swept antenna coordinate, and a list of discrete angles for the unswept coordinate.

There is a duality between the PPI and RHI scans in that the lists and limits that apply in one case can be carried over to the other case by reversing the roles of azimuth and elevation.

Elevation for PPI Full and PPI Sector Scans

To set up the antenna elevation limits for a PPI Sector and PPI Full scans, enter the list of elevation angles to be used on successive sweeps:

1. Select Elevation button to show a window containing up to 40 elevation angles and make your selections.
2. Select Apply > Exit. (Select Clear to start over.)

When you finish editing, the menu entry shows the number of specified tilt angles and the minimum and maximum angles.

Azimuth for PPI Full Scans

Azimuth and Elevation for PPI Sector Scans

When a PPI Sector scan runs, the antenna scans back and forth between the azimuth limits at a rate that achieves the requested azimuthal resolution between each processed ray. The first sweep of the scan is performed using the first elevation angle from the elevation list; the second sweep using the second angle, and so on.

To set up the antenna azimuth limits for a PPI Sector scan, enter the start and stop angles, in the Azimuth field, type the limits to the nearest whole or 1/10°. The following table shows an example of how the sector is defined clockwise from the first limit to the second limit.

Azimuth and Elevation for RHI Scans

For RHI scans, the set-up procedure is similar to PPI Sector, except that you:

• Enter the start and stop limits in the Elevation field.
• Enter the angle list in the Azimuth field.

The elevation limits for RHI scans are constrained by the limits specified in the setup utility. See IRIS and RDA Utilities Guide (M211316EN).

Azimuth and Elevation for Manual Scans

For manual scans, the Elevation and Azimuth fields show NA because the antenna is controlled interactively.

Resolution

The resolution is the required spacing between successive data rays in the scanned direction.

You can select a resolution from a menu or type the value in the field.

Resolution for PPI Full and PPI Sector Scans

For PPIs, specifying 1.0° resolution means that for every degree of azimuth there is a new set of samples of, for example, the reflectivity at all ranges. The range is limit 0.352 .... 2.000.

During PPI scanning, antenna and signal processing are coordinated so that data are collected at the specified resolution interval. Sampling is the nearest N*(Resolution) starting with 0°.

For example, if the resolution is 1.0, rays of data are collected at 0, 1, 2, ... degrees. If the scan speed is set to Auto, the PPI antenna scan rate is adjusted automatically to scan as rapidly as possible to achieve the requested resolution.

The Radar Status shows the achieved scan rate.

Resolution for RHI Scans

In RHI scans, the elevation angular velocity used for the scan is not constant. A fixed velocity results in too much time being spent at high elevation angles where only the initial 20 km (or so) of the ray contains useful data. Also, too little height resolution would be obtained for low elevation angles and far ranges. To compensate, the elevation velocity for RHI scans is a function of the elevation angle itself — the velocity increases as the angle increases.

For RHI scans, IRIS picks and displays the closest Resolution between 0.2, 0.4, 0.6, and 0.8.

The selected resolution represents the desired angular ray spacing at 0° elevation. This generally corresponds to a small elevation velocity near 0°, but by the time the antenna reaches its zenith the elevation velocity is approximately 10 times greater. The RHI velocity algorithm attempts to maintain constant distance spacing along the maximum range and height boundaries of the scan to produce a properly filled data presentation.

Resolution for Manual Scans

For manual scans, IRIS picks and displays the closest Resolution among 90, 180, 270, and 360, either continuous or non-continuous.

If you plan to use manual scanning, you must pre-configure scans for the situation. Specify the number of rays of data that you want stored (up to 1024 angles or rays) and how long IRIS should continue to collect data, as follows:

For more information, see Scheduling and Running Manual Scan Tasks.

Scan Speed

When testing a task, observe the actual scan rate in the Radar Status Menu.

If you are in the Auto mode, you can tune the scan rate by changing the fields in the radar status menu and then retesting. For example, to increase the scan rate in Auto mode, you can:

• Increase the PRF
• Decrease the number of Samples
• Decrease the scan Resolution

For more information, see the setup/ingest utility in the IRIS and RDA Utilities Guide (M211316EN).

Pulse Width

Some systems support multiple pulse widths.

Select the pulse width in microseconds (for example 1.0 μsec). IRIS picks the closest available value.

Most systems support one or more of 0.50, 1.00, 2.00, and 5.00 μsec.

The PRF is automatically reduced to the maximum permissible value if the new choice exceeds the duty cycle limit of the transmitter.

Polarization

This field is available for dual polarization systems. The following table shows the polarization options.