Data Corrections

Clutter Map Z

When no Doppler filtering is available, you can use clutter mapping to remove clutter.

Make a volume scan in a weather situation without any precipitation to represent typical clutter in your images.
Tag this product as Clutter Map in the Ingest Summary menu, and turn it on in the task configuration.

It modifies the Z data to remove any signal weaker than the clutter scan.

Alternatively, to remove clutter from the RAIN1 products, tag a RAIN1 product as clutter map.

Target Detect Zc

Target Detect Zc computes Zc with uniform weather removed. Any input signal of more than 2 range bins in a row is smoothed and then only peaks are passed. The goal is to pick out targets against a weather background.

Only use Target Detect Zc for target tracking.

Beam Blockage Zc

Because of obstructions to the radar horizon (towers, buildings, mountains) the radar beam can be partially or totally obstructed.

Use Beam Blockage Zc to use the Ingest process to compute Zc by correcting the measured Z values for partial beam blockage.

Beam Blockage Zc can make corrections up to 10 dB. Larger corrections (for example, more than 90% of the beam power lost) are not practical.

To use beam blockage, you must configure the beam_block.conf file in the IRIS configuration directory (/etc/vaisala/irisrda) .

For example, configure the file for each elevation angle used in the volume scan:

Azimuth angle span
Range at which the blockage starts
Blockage in dB up to 10 dB
Elevation angle tolerance

For more information on the file format, see the example beam_block.conf file shipped with your system.

These feature works best when dynamic angle synchronization is used so that the azimuth rays are collected over the same angle span every time (or example, for 1° resolution, the angle spans would be 0.5 ...1.5, 1.5 ... 2.5, and so on).

The blockage correction is based on the assumption that part of the beam is blocked, and part continues on to reflect from weather targets. Thus all signal returns beyond the blockage have a lower power than the correct value. To correct for this, IRIS adds the appropriate constant to all range bins beyond the blockage. There is no correction to handle complete beam blockage. Up to 2 beam blockages are supported in each direction.

Unfold Vc

Use VVP unfolding to unfold Doppler speeds in individual range bins, when the value is compared to a reference VVP product.

Unfolding for IRIS-corrected velocity, Vc, is especially important for NDOP (Multiple Doppler) product. For more information, see IRIS Product and Display Guide (M211319EN).

You must create a reference VVP product with a product name UNFOLD to perform this correction.

Attenuation Zc

Attenuation Zc computes a Zc by correcting for the intervening attenuation.

In the Ingest setups, set a Z attenuation constant and exponent, maximum Z for correction and maximum cumulative correction. For each task, decide if you want to use the attenuation correction.

Values are suggested for X- and C-bands. Vaisala does not recommend the attenuation option for S-band.

If multiple corrections are turned on for Zc, the order of operations is:

Beam blockage
Intervening attenuation
Target detection

Remove Fallspeed in Vc

Radial winds are assumed to be caused by the horizontal winds only. The fallspeed of the hydrometeors (of order 1 m/s for snow to 10 m/s for rain) can make a significant contribution to the radial velocity.

To estimate and remove this effect, the water phase (snow or rain) of hydrometeors must be known. If you use this correction, add the height of the melting level to the setup information. This correction is mainly used when making the NDOP product.

See SRI product in the IRIS Product and Display Guide (M211319EN) for information on setting the melting level dynamically.

Storm Relative Vel Vc

Removes the storm motion from the radial velocities. The source of the storm motion is an IRIS FCAST product, which you must configure with a product name STORM.