WMOD00521

• Project Name: Project Skywater
• Title: Project Skywater SWR-75 Radars
• Date: 3/28/1978
• Weather Modification - Doc Type: Report

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i by 16, 32, 64, or 128 and are placed in a
storage register. At the same time, the shift
registers are zeroed so that no residue values
~e left from succeeding azimuths.

""this is not a free running DVIP but rather a
block DVIP, the DVIP has the capability of dis-
playing 17 levels of discrete contouring in
shades of black, dark gray, light gray, and
white. These display functions are dialed in by
thumb wheels at each of the 17 levels. The DVIP
was designed for 17 levels which are in 5-dB
steps across the 85-dB dynamic range of the
logarithmic receiver. The resolution of the
DVIP is 1/3 dB; therefore, across the 17 level
8S-dB range there can be equated 0 to 255 units
called DVIP's. Each DVIP unit represents
1/3 dB, and 15 DVIP's represent the 5 dB between
each of the 17 levels. The DVIP is set up so
that level 4 is equal to a power return of
, -101 dBm, then level 5 is -96 dBm, and so forth
to level 17, which is -36 dBm. The lowest value
that can be realistically processed by the DVIP
is -103 dBm, at which time the logarithmic
receiver curve flattens out and logging takes
over. A value of -103 'dBm is the equivalent of
39 DVIP units, and any signal below this limit
is lost in the noise. A "Blue Sky" elimination
feature is incorporated in the DVIP, and a
39-DVIP elimination level is set on the control
switch so that any radial that does not contain
a signal above the -103-dBm level will not be
recorded, This feature results in a tremendous
saving in magnetic tape and in processing time.

On the face of the DVIP drawer is a row of 17
lights to allow easy recognition of the
intensity of the returned signal. The returned
~nal, which has been averaged in range,
~uth, and time, will cause an appropriate
level light to be illuminated. Every range bin
could have a different averaged signal, and
therefore it would be possible to have more
than a single light illuminated at a given time.
It is possible to determine the 'maximum value of
the averaged returned signal by noting the
highest valued level light that is illuminated.
The intensity of the cloud echoes can be deter-
mined by utilizing a row of 17 switches imme-
diately below the level lights. These switches,
when activated at a particular level, will
remain activated until reset. As a result of the
level switch activation, only video equal to or
greater than the selected level will be dis-
played. Therefore, by successively increasing
the level of suppression, the maximum intensity
to within 4.67 dB of its actual value can be
determined for any desired cloud echo.

As mentioned previously, each of the 17 levels
can be displayed as a black, dark gray, light
gray, or white area on the PPI or RHI scopes.
Proper selection of the level brightness pro-
vides a contour pattern which allows recognition
of areas of equal intensity within a cloud echo
and the associated values of dBz which are
occurring. Areas with strong gradients of
reflectivity may cause uncertainties if there
are too many repetitions of the black-through-
bright selections.

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The radar has the capability of three modes of
operation during data recording. These modes
are known as A mode, A+B mode, and RHI, The
A mode and the B mode have independent selection
of PRF and samples to be averaged. The A mode
may operate independently, but the B mode can
only be operated in conjunction with A mode,
thus the connotation A+B mode. The A mode is
used when it is desired to record a fixed eleva-
tion angle. This fixed angle is selectable to
the nearest tenth of a degree using' the three
thumb wheel switches in the A scan window on the
operator's control console.

The B mode is used in concert with the A mode
when recording a sequence of 3600 azimuth scans
at increasing elevation angles to form a volume
scan. The B mode start and stop elevation
angles are operator-selectable to the nearest
degree by use of thumb wheel settings in the
B Mode Start and B Mode Stop dials. The eleva-
tion angles to be recorded are controlled by an
Elevation Increment switch, which is selectable
at 0.50, 10, 20, or 30. A volume scan consists
of the 3600 scan at the preset A scan elevation
angle; the 3600 scan at the elevation of the
B Mode Start; the 3600 scans at each elevation
increment be~een B Mode Start and B Mode Stop,
and the 3600 scan at the elevation angle equal
to the B Mode Stop. During recording of a
volume scan, no data are recorded during the
transitory period of the antenna step from one
elevation to the next plus a 3-second delay.
This delay was incorporated to allow the antenna
damping to settle out. After this delay has
timed out, a 3600 scan is initiated and no data
are lost at any elevation.

The A mode and/or the A+B mode may be initiated
in either of two ways. The Point of Control
switch on the Operator's console must be in the
AUTO position in either case. The Single Record
switch may be depressed and one A mode scan or
one A+B mode volume scan are immediately
initiated. At the completion of either mode,
no further recording.w~~ld be done until_ th~_
Single Record switch is depre$sed again. A series
a-f' Single Record switch depressions would give
sequential volume scans. If it is desired to
take a series of A scans or volume scans, it
would be easier to initiate this sequence by
use of the automatic Timer. The Timer will
repeat the sequence at intervals of I, 2, 5, 10,
15, or 30 minutes, or continuously. Once the
Timer is preset, depressing the Start Timer
switch will activate the selected sequence 20
seconds after releasing the switch. A "beep"
will be heard as. the. Start Timer switch is
depressed and the "beep" will b. heard again
after the end of any sequence time except in
the Continuous position. The A mode scan or
A+B volume scan will be repeated until such
time as the Timer is switched off or the Point
of Control is switched from AUTO to RADAR.

The RHI mode of recording is initiated by
switching the Elevation Mode on the RHI controls
to AUTO. The PRF rate and the samples to be
averaged are controlled by the A mode scan
switches. The upper limit for the RHI scan is
controlled by the B Mode Stop' switch, while the
lower limit is always at zero, The antenna scan
rate during RHI recording moves at the slowest