If the DWELL product is based on a PPI product where the elevation selection in the PPI
product configuration is set to the wild card *, then you must take care in scheduling to
avoid excess CPU loading and performance degradation.
To prevent the DWELL product being produced on the completion of every PPI
sweep,Vaisala recommends that you set the Product Scheduler > Skip Time to the time
required to complete a volume scan or longer.
Input Product Filters
You can apply the following input data filters to each input product before it is merged into
the DWELL:
• Min Filter
Discards any pixel in the input product with data value less than the specified minimum
value. For velocity, absolute value is used.
For the example of a PPI in dBZ, if the minimum value is set to 10 dBZ, all pixels with
values less than this are discarded.
• Max Filter
Discards any pixel in the input product with a data value greater than the specified
maximum value. For velocity, absolute value is used.
For the example of a PPI in of dBZ, if the maximum value is set to 50 dBZ, all pixels in
the input product with values greater than this are discarded.
• Contrast Filter
Discards any pixel in the input product with data value not exceeding the
corresponding data value in the computed background field plus a selectable
threshold. For velocity, the absolute value of the dierence between the background
field and input product pixel is used. The background field is obtained by first creating a
smoothed version of the DWELL product.
For the example of a VIL product, if the contrast threshold is set to 3 (mm) (0.12 in),
then a pixel in an input product must have a VIL 3 mm (0.12 in) greater than the
corresponding pixel in the background field.
If a pixel fails any of these tests, then it is set to thresholded, that is, no data.
Data Merge
After filtering, each pixel in the input is "merged" into the corresponding pixel in the DWELL
output. If, for example, there are 10 input products to merge, there can be up to 10 possible
values for assigning the output value. The merge algorithm uses the maximum value. In the
case of velocity, the absolute value is used.
Depending on the user selection, the algorithm then stores either the time of the merged
pixel or its data value. Time is stored as the "age" of the pixel relative to the most recent
input product in the DWELL sequence.
In the case of merging WARN products, the centroid statistics are merged together, that is, a
new WARN product is created that combines all of the centroids in the time sequence of
input WARN products.
IRIS Product and Display User Guide M211319EN-H
144 RESTRICTED
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