WMOD00417

• Title: Computer Processing of Digital Radar Data Gathered During HIPLEX
• Date: 4/4/1978
• Weather Modification - Doc Type: Report

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TABLE 3. Contents of optimally compressed archive file.

JOURNAL OF APPLIED METEOROLOGY

VOLUME 17

Parameter

Units

Site location
Year
Date
Time
Antenna azimuth
Antenna elevation
Maximum and minimum antenna elevation
of recorded data
Aircraft locations
Range delay
Range interval
Azimuthal recording mode
Elevation recording mode
Sampling average
. Pulse repetition frequency
Antenna scan mode
Noise level
Reflectivity values

calenda,r
Julian
h, min, s
deg
deg

deg
km
km
km
code
code
code
code
code
DVIP
DVIP

The compressed file created during this step conta.ins
only data for bins which exceed the computed noise
level. This results in a significant size reduction which
is most convenient for long-term storage. In fact,
when archived on 1600 cpi magnetic tape, a space
reduction of 10: 1 occurs when compared with the raw
data. The contents of this optimally compressed archive
file are listed in Table 3.

b. Err.or correction and B-scan compositing

This step provides the analyst his first glimpse of
processed data. Inputs are the raw, compressed data on
disk and a file describing the corrections to housekeep-
ing data. As the error correction functions are per-
formed, a single B-scan and PPI, representing all data
from all sweeps taken within a 5 min volume scan, is
composited.
Since the composite B-scan is a tool to be used for
'delineating cloud complexes, identifying mergers and
characterizing precipitation, the maximum equivalent
reflectivity (Z.) factor between two horizontally and
vertically adjacent bin values is displayed. The printed
characters represent the maximum radar reflectivities
which occurred at any given range-azimuth location
during a volume scan. B-scan and PPI formats are
also used to display echo tops for each volume scan.
This step also accumulates the number of data points
(bins) from each elevation angle in the volume scan
which exceed the noise and reflectivity thresholds re-
quested, computes the number of points contributed at
each elevation, and prints a summary at the end of
each composite. A sample of a portion of a composite
B-scan and a sample of a composite PPI are shown in
Figs. 3 and 4, respectively.
The file produced by this step is the Archival File
which is a corrected version of the optimally com-
pressed file generated during the edit phase. This jile

is recorded on magnetic tape, contammg the three-
dimensional information at its basic recorded resolution.
About 10 files can be recorded on one tape which is then
duplicated (for backup purposes) and permanently
stored in the Bureau of Reclamation tape library.
After about a year the raw data tapes are degaussed,
cleaned, verified, and used again at the field sites.
Location and identification of echo cells are accom-
plished with the composite B-scans. Presently only 20
dBZ and greater reflectivities are being displayed.
Extreme flexibility exists for the manner in which a cell
is defined. A "cell" can be defined minimally as a
single range bin, or for all range bins recorded. One
technique being used to identify cells for an extensive
study is described below.
Cells are identified if they lie between 25 and 150 km.
If a cell touches the inner or outer range boundary it
must extend at least 20 km into the area of concern,
or have at least one separate peak of 30 dBZ or greater.
Naming of the cell entity is done at this time. The ob-
jective rules for the 10 position (AAAABCDEFG)
identification are as follows:

1. AAAA: 4--position cell number from 1 to 9999
2. B: number of peak reflectivity values between 30
and 39.9 dBZ
3. C: number of peak reflectivity values between 40
and 49.9 dBZ
4. D: number of peak reflectivity values greater than
49.9 dBZ
5. E: cell origin and seeding status code according to
the following table:

First Pre-
Echo Split existing
No seed N Z V
AGI seed A X T
Hygroscopic seed H Y U

6. F: boundary code to indicate whether or not the
echo entity is a complete echo
7. G: number of cells that have merged into the
system.

Whenever a number is required, as in positions B, C,
D and G, characters 0-9 and A-Z may be used. For
example, 0032E73ZN4 would identify a study case as
cell number 32, 14 peaks between 30 and 39.9 dBZ,
7 peaks between 40 and 49.9 dBZ, 3 peaks greater than
49.9 dBZ, the unseeded cell originated through a split
of another cell, it is a complete cell entity, and 4 cells
have merged into this one cell system thus far.
This method of identification allows for a significant
amount of cell description at the same time as making
it adaptable to automatic echo identification and track-
ing, which has been developed following the processes
being described. The option for manually identifying
and tracking cells will continue.