Use the Skip Time field if you want only the accumulations for specific time intervals. You
can set the skip time to any multiple of the accumulation period. For example, if you want a
3-hour integration only for the periods ending at 03:00, 06:00, 09:00, ..., set the Skip Time
field to 03:00.
If the RAIN1 input is corrected by means of raingage input data, then there is a delay in
the CATCH product since the input RAIN1 product is delayed as it waits for the arrival of
the raingage data.
Scheduling CATCH products is the same as scheduling RAINN products.
More information
‣
RAIN-N: N-Hour Rain Accumulation (page 59)
5.1.4
CATCH Algorithm
The CATCH product algorithm takes the RAIN1 products for the specified integration time
(hours) and performs the following steps:
1. For each subcatchment, all pixels in the RAIN1 product that are within or touching the
subcatchment perimeter are added together and then divided by the total number of
pixels.
Thresholded pixels are treated as 0 rainfall.
The result is the average hourly rainfall for the subcatchment.
2. This is repeated for each hour and each subcatchment.
3. The sum over all hours in the integration time is taken for each subcatchment to get a
total average accumulation for the time period.
If the Issue Warn button is enabled, this sum is checked against the catch file warning
threshold (adjusted by the Oset and Multiplier) and a single IRIS warning is issued for
all subcatchment areas that exceed the threshold.
For each subcatchment, the final output file contains:
• The LAT/LON of the label point, the point name and index number.
• The hourly average accumulations over the selected integration time.
These are used for the bar graph display.
• The total average accumulation for the integration time.
• The fraction of pixels in the subcatchment that had non-zero precipitation.
The output file does not contain the subcatchment boundary definitions. This has
implications for display when the CATCH product is transferred to another machine. See
Displaying CATCH (page 126).
Chapter 5 – Configuring and Scheduling Optional IRIS Products
RESTRICTED 125
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