4. Define IRIS Setup configurations.
a. In Setup > Input, specify the input characteristics of the user raingage files including
the directory where the files arrive and the name of the Input Pipe that is used to
reformat the data in the IRIS GAGE product.
See IRIS and RDA Utilities Guide .
Depending on your system there may also be a .conf file for the Input Pipe. The
input pipe is stored in /usr/sigmet/config/pipes.
b. In Setup > Product, configure the default Z-R relationship.
Typically this is set to Z=200R
1.6
(input 200 and 1.6). However, you can set it
dierently based on local experience.
Note that you can override this in the RAIN1 product configuration.
c. In Setup > Product, configure the GAGE Wait Time.
This is the time required after the end of the hour for the GAGE product to be
generated. The delay is primarily caused by the delay in the arrival of the user
raingage data over the network.
E.5 Algorithm for RAIN1 Gage Calibration
The default raingage correction algorithm provided is modeled after Brandes and Wilson
(1982). The algorithm uses a basic time step of one hour, that is, GAGE totals for each hour
are compared to the hourly radar totals (based on a default Z-R relationship) for the same
hour. The ratio (1-hour gage accumulation/1-hour radar accumulation) is the correction
factor for a gage.
The RAIN1 product is then corrected by interpolating the correction factors for all of the
gages to each pixel in the RAIN1 product and multiplying the radar pixel value by the
correction factor. The basic algorithm steps are as follows:
1. Gage Correction Factor Calculation for Each Gage
The gage correction is the ratio of the (1-hour gage accumulation)/(1-hour radar
accumulation).
• The gage accumulation is taken from the GAGE product. It must be greater than the
Minimum Valid Gage Accumulation for a gage correction factor to be calculated.
• The radar accumulation for the gage is calculated by first making an uncorrected
RAIN1 product for the hour and then averaging the pixels surrounding the gage
(according to the Averaging Distance - see Configuring RAIN1 with Raingage
Correction (page 368)).
The pixels are averaged by summing only the valid (non-thresholded) pixels and
then dividing by the number of valid pixels.
For a gage correction to be calculated, the average rainfall accumulation must be
greater than the Minimum Valid Radar Accumulation, and the number of valid (non-
thresholded) pixels must be greater than the Minimum Percentage Radar RAIN1
Coverage.
• If both the gage and radar 1-hour accumulations are valid, then a gage correction is
calculated for the gage. Otherwise, the gage is flagged as invalid.
• The maximum and minimum correction factor limits are then applied.
• This procedure is repeated for each gage.
Appendix E – Hydromet Raingage Correction
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