Baron Services DSSR-250C Host Computer Commands
RVP8 User’s Manual
March 2006
Host Computer Commands
6. Host Computer Commands
This chapter describes the digital commands that the host computer must use to set up and
control the RVP8 processor for recording data. Each command is described in detailed in a
separate section of this chapter. Note that a command mnemonic, or shorthand reference name,
is given in each section heading. These names are frequently used to refer to particular
commands.
The write–up for each command includes a description of what the command does and a
pictorial layout of the bits in the 16-bit command word. Commands consist of an initial
command word containing an opcode in the low five bits. If additional arguments are required,
they are listed as “Input 1”, “Input 2”, etc. Finally, if the command produces output, those
words are listed as “Output 1”, “Output 2”, etc. Often each word is broken down into several
independent fields, each consisting of one or more bits. In such cases, the pictorial layouts show
the placement of the bit fields within the word, and each field is described individually. All data
transferred to or from the RVP8 are in the form of 16-bit words.
Before attempting to program the RVP8, it is a good idea to at least skim through the
descriptions of every command. The instruction set has been designed to be as concise and
orthogonal as possible. User programs should always execute the IOTEST command on
power-up to ensure that the interface connections are all intact. The diagnostic result registers
from GPARM should also be checked initially to verify that the RVP8 passed all internal checks.
Since all internal RVP8 tables and parameters are set to reasonable values on power-up, it is
conceivable that PROC commands could be issued immediately to acquire and process radar
data. More realistically, however, the default information is first modified to meet the users
needs.
To set up for data acquisition and processing the following sequence of commands might be
executed. Trigger and pulse width are first established using the SETPWF commands. Range
bin placement and processor options are then chosen using LRMSK, and SOPRM, and receiver
noise samples are taken with SNOISE. The noise levels are not automatically sampled on
power-up, so SNOISE must be issued at least once by the user. LFILT is executed if clutter
filters are needed. If data rays are to be synchronized with antenna motion, then LSYNC is used
to specify a table of antenna angles. After all setups are complete, PROC commands are issued
to actually collect, process, and output the data. Errors detected during the execution of
commands are noted by the RVP8 and can be monitored using GPARM.
The RVP8 contains a 4096-word first-in-first-out (FIFO) buffer through which all output data
flow. This buffer is included to simplify the requirements of the user’s interface hardware. The
FIFO holds each sequential word generated by the RVP8 until such time as the user is ready to
accept it. Thus, when reading from the processor, it is permissible to fall behind by as many as
4096 words before any slowdown in performance occurs. The RVP8 writes to the FIFO at full
speed as long as it is not full, and the internal processing is not affected by the exact speed at
which user I/O actually occurs. This continues as long as the average I/O rate on, perhaps 10ms
intervals, matches the average rate at which data are being produced.
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The sequence of events described above is altered when the FIFO becomes completely full.
Then, when the processor generates the next output word, it waits in an idle loop until the user
makes room in the FIFO by reading out one or more words. Until this space becomes available,
the RVP8 simply waits and does not proceed any further with its internal processing. This, of
course, leads to a slowdown in performance, but it is not a disastrous one. The user always
obtains correct data no matter how long it takes to read it. One could take advantage of this fact
to synchronize the acquisition of data by the RVP8 with the post-processing and display of that
data by the user. In this case, RVP8 would be instructed to output data at the maximum rate, the
user would read these words at the user’s maximum rate, and the overall system would
automatically run at the slower of those two speeds.
When the output FIFO is full and the RVP8 has the next word ready for output, there is another
way that the idle wait loop can be exited, that is, if the processor detects that the user is
performing a write I/O cycle. Since the user should have been reading data by now, the presence
of a write cycle is taken to mean that some more important condition has arisen. As such, the
wait loop is terminated and the RVP8 accepts the write data soon afterward. If the new data are
commands, they are executed right away, but any output they try to produce may be lost in a
similar manner. The net effect is that the processor continues to execute all commands correctly,
but that their output is discarded.
The discarded output data are not in fact lost. Rather, the data are eventually replaced with an
equal number of zeros. Each time the RVP8 discards an output word, it also increments an
internal 24-bit count. When FIFO space becomes available in the future, the processor replaces
all of the missing data with zero-valued placeholders.
Writing when the FIFO is full can be particularly useful if the new command is a RESET which
calls for clearing of the output FIFO. When the RESET is processed, all past and present output
data are discarded, leaving the RVP8 output section completely empty. This is useful whenever
the processor has pending output data which the user wants to truly throw away.
6.1 No-Operation (NOP)
This single-word instruction is simply ignored by the the Signal Processor. The NOP is useful
when a number of words are to be flushed through the RVP8 with no side effects.
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| | | | | | | | | | | | | | | | |
| | 0 0 0 0 0 | Command
|___________________________________________|___________________|
6.2 Load Range Mask (LRMSK)
This command informs the signal processor of the ranges at which data are to be collected. An
arbitrary set of range bins are selected via an 8192-bit mask. The Nth bit in the mask determines
whether data are acquired and processed at a range equal to RES x (N-1). The Range resolution
is specified by a TTY setup question (see section 3.2.5), in the range 25 through 1000 meters.
Any collection of ranges may be chosen from integer multiples of that distance. The example
below is given for the default resolution of 125 meters. The range mask is passed to the RVP8
packed into 512 16-bit words. The least significant bit of each packed word represents the
nearest range, and the most significant bit represents the furthest range in each group of 16.
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According to the range bins that are selected in the mask, the signal processor computes and
stores internally a range normalization table which is later used to convert receiver intensity
levels into reflectivity levels in dBZ. Note that the LRMSK command implicitly specifies the
number of bins to be processed and output. The maximum bin count is 3072, though depending
on the computational intensity of the configuration, the RVP8 may be able to compute fewer
bins. If the number of bins selected in the bit mask exceeds this maximum, the trailing bins are
truncated. If the new mask does not specify any active bins, then a single bin at range zero is
forced on. The default power-up mask selects 256 bins equally spaced by 1.0km starting from
zero range.
Range averaging is also determined by LRMSK. The upper byte of the command controls how
many consecutive bins are grouped together. A value of zero means no averaging; one means
that pairs of samples are averaged; 255 means that 256 terms are summed, etc. The individual
samples that go into each average are still taken according to the bits that are set in the mask,
except that they are now grouped together so that only one net bin results from the several data
samples. Note that the limitation of 3072 sampled ranges applies to the bin count prior to
averaging.
For example, suppose 100 bits are selected in the range mask and no averaging is elected. Then
parameters are computed at those 100 ranges, and 100 bins of data are output. If the averaging
were set to one, rather than zero, samples would still be taken at the same ranges, but pairs of
bins would be averaged together and only 50 ranges would result. Note that the parameters are
averaged by summing the autocorrelations for each bin. The range normalization value
associated with the averaged bin is computed according to the midpoint of the first and last
sample.
Incompletely averaged bins are discarded by the LRMSK command. In the above example, if
the averaging were set to two so that triples of samples were summed, then only 33 bins would
be output. This is because the 100-bit mask left a dangling 100th sample. In the extreme case
where there are not enough mask bits to result in even one complete bin, the RVP8 forces the
averaging to zero and turns on a single bin at zero range.
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| | | | | | | | | | | | | | | | |
| Range Avg. (See Text) | | 0 0 0 0 1 | Command
|_______________________________|_______|___|___________________|
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| | | | | | | | | | | | | | | | |
| Bits for ranges 0.000km to 1.875km | Input 1
|_______________________________________________________________|
\_1.875 . \_0.000
.
.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Bits for ranges 1022.000 km to 1023.875 km | Input 512
|_______________________________________________________________|
\_1023.875 \_1022.000
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6.3 Setup Operating Parameters (SOPRM)
This command is used to configure the Signal Processor. The command should be issued
whenever any of the parameters in the list change. The default parameter list consists of twenty
16-bit input words. These can be followed by optional XARG parameters as needed.
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| | | | | | | | | | | | | | | | |
| |NTh| | 0 0 0 1 0 | Command
|___________________________|___|___________|___________________|
NTh If 1, then no threshold values are set. This means ignore input words 4, 5, 6, 7,
11, 12, 13, 14, and 18. This is usually used in conjunction with the THRESH
command (see section 6.29), when setting individual thresholds.
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| | | | | | | | | | | | | | | | |
| Sample Size | Input 1
|_______________________________________________________________|
The sample size is continually adjustable from 1 to 256 pulses. However, during the alternating
polarization mode, the sample size must be even. If an odd value is entered it is rounded up by
one in that case.
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| | | | | | | | | | | | | | | | |
| | Polar |NHD|ASZ|16B|CMS| R2| |3x3| | |Lsr|Dsr|Rnv| Input 2
|_______|_______|___|___|___|___|___|___|___|___|___|___|___|___|
Each of the single-bit fields selects whether the given processing or threshold option is enabled
(1) or disabled (0).
Polar Configures transmit polarization and Zdr processing:
00 – Fixed polarization, Horizontal
01 – Fixed polarization, Vertical
10 – Alternating polarization pulse-to-pulse
11 – Dual simultaneous transmission
NHD Disables inclusion of header words in the processed data that are output by the
PROC command (See also, CFGHDR command).
ASZ The “Any Spectrum Size” bit requests that DFT processing algorithms, clutter fil-
ters, spectral output, etc. all operate on spectra whose size exactly matches the
number of available pulses (rather than rounding the spectrum size down to the
next lower power-of-two).
16B Configures for 16-bit (rather than 8-bit) data output from the PROC command.
This bit affects the single-parameter versions of Reflectivity, Velocity, Width, and
Zdr data. However, the PROC command’s archive format always holds 8-bit data,
regardless of the setting of 16B. This gives the option of extracting both 8-bit and
16-bit data simultaneously from each ray.
CMS Enables Clutter Microsuppression, in which individual range bins are rejected
(based on excessive clutter) prior to being averaged together in range.
R2 Use three lag (R0/R1/R2) algorithms for width, signal power, and clutter correc-
tion.
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3x3 Switches on the 3x3 output filter (See Section 5.3.3). The RVP8 automatically
handles all of the pipelining overhead associated with running the 3x3 filter, i.e.,
valid output data are always obtained in response to every PROC command.
Lsr Reflectivity speckle remover. When set, range speckles in the corrected and un-
corrected reflectivity data are removed.
Dsr Doppler speckle remover. When set, range speckles in the velocity and width data
are removed.
Rnv Range normalization of reflectivity data. This bit also enables intervening gas at-
tenuation correction.
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| | | | | | | | | | | | | | | | |
| Log Slope 65536 * dB / (LSB) | Input 3
|_______________________________________________________________|
This number defines the multiplicative constant that converts the signal power in dB to the units
of the 12–bit “Log of power in sample” time series outputs. One fourth of this slope is used to
generate the “Log of Measured Noise Level” output from GPARM (word 6). The recommended
value to use here is 0.03 (1966). This gives a dynamic range of 122 dB in 12 bits.
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| | | | | | | | | | | | | | | | |
| LOG Threshold in 1/16 of dB | Input 4
|_______________________________________________________________|
Reflectivity values below this level can result in thresholding of data, if the threshold control
flags (see below) include LOG Noise bits. The threshold value is always non-negative, and the
comparison test is described in Section 5.3.
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| | | | | | | | | | | | | | | | |
| Clutter Correction (CCOR) Threshold in 1/16 of dB | Input 5
|_______________________________________________________________|
The clutter correction threshold is a bound on the computed log receiver adjustment for clutter.
These corrections (in dB) are always negative. Any clutter correction which is more negative
than the above value can result in thresholding of data.
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| | | | | | | | | | | | | | | | |
| | SQI Threshold | Input 6
|_______________________________|_______________________________|
The Signal Quality Index (SQI) threshold is an unsigned binary fraction in the range 0 to
255/256. When the SQI for a range bin falls below the stated value it may result in thresholding
of data.
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| | | | | | | | | | | | | | | | |
| Weather Signal Power Threshold in 1/16 of dB | Input 7
|_______________________________________________________________|
Weather Signal Power (SIG) is an estimate of the SNR of the weather component of the received
signal. When the SIG (see Section 5.2.12) falls below this comparison value it may result in
thresholding of data.
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| | | | | | | | | | | | | | | | |
| Calibration Reflectivity in 1/16 of dB | Input 8
|_______________________________________________________________|
Host Computer Commands
The calibration reflectivity is referenced to 1.0 kilometers.
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| | | | | | | | | | | | | | | | |
| | TopMode | | Input 9
|_______________|_______________|_______________________________|
The TopMode bits select the overall data acquisition and processing mode for the RVP8.
Although the processing algorithms that are used in each top level mode are quite different, the
RVP8 command set works in a uniform way in all modes.
0000 Pulse Pair Processing Mode. Doppler clutter filters are 4th-order IIR high pass;
data are processed one pulse at a time as each pulse arrives (see Section 5.2.3).
0001 FFT Processing Mode. Doppler clutter filters use nonlinear frequency-domain
approach; data are processed in batches of pulses (see Section 5.2.2).
0010 Random Phase Processing Mode. Data from first and second trips are dealiased in
range based on knowledge of the radar transmitter phase (see Section 5.7).
0100 DPRT-1 Processing Mode. The trigger generator produces alternate short and long
pulses, and Doppler autocorrelations are computed using only the short pairs (see
Section 5.5).
0101 DPRT-2 Processing Mode. The trigger generator produces alternate short and long
pulses, and Doppler autocorrelations are computed using both pairs (see Section
5.5).
11XX Four codes reserved for custom user modes.
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| | | | | | | | | | | | | | | | |
| |UVD|PCT| Window |ZER| Filter Stabilization Delay | Input 10
|_______|___|___|___________|___|_______________________________|
The RVP8 clutter filters are controlled by this word.
Delay This delay is introduced prior to processing the next ray of data whenever Dual-
PRF velocity unfolding is enabled or the RVP8 has been reconfigured by user
commands. The delay permits the clutter filter transients to settle down following
PRF and gain switches. The value is specified as the number of pulses, and hence,
the number of filter iterations, to wait.
ZER If set, then the clutter filter’s internal state variables are zeroed prior to waiting the
delay time. For some signal conditions, this may give better results than allowing
the filter to naturally flow into the new data.
Window Selects the type of window that is applied to time series data prior to computing
power spectra via a DFT. Choices are: 0:Rectangular, 1:Hamming, 2:Blackman,
3:Exact Blackman, 4:VonHann.
PCT If set, the RVP8 will attempt to run its standard processing algorithms even when a
custom trigger pattern has been selected via the SETPWF command.
UVD Unfold velocities using a simple (V
high
– V
) algorithm, rather than the standard
low
algorithm described in Section 5.6.
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15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Threshold Control Flags for UnCorrected Reflectivity | Input 11
|_______________________________________________________________|
Host Computer Commands
These flags select which threshold comparisons result in unCorrected reflectivity being accepted
or rejected at each bin. There are four test comparisons that are made at each range, as described
above for input words 4, 5, 6, and 7. Each test either passes and produces a code of 1, 2, 4, and
8 respectively, or fails and produces a code of zero. The sum of the codes for each of the four
tests is a number between 0 and 15, which can also be interpreted as the following four-bit
binary number:
3 2 1 0
| | | | |
| 8 | 4 | 2 | 1 |
|___|___|___|___|
\ \ \ \___ LOG Threshold Passes
\ \ \______ CCOR Threshold Passes
\ \_________ SQI Threshold Passes
\____________ SIG Threshold Passes
The individual bits of the Threshold Control Flag word each specify whether data are to be
accepted (1) or rejected (0) in each of the sixteen possible combinations of threshold outcomes.
Thus, the pattern of bits in the flag word actually represents a truth table for a given logical
function of the four threshold outcomes.
The following examples show actual values of the Flag word for the stated combinations of
acceptance criteria:
Value Criteria
FFFF All Pass (Thresholds disabled)
0000 All Fail (No data are passed)
AAAA LOG
8888 LOG and CSR
A0A0 LOG and SQI
8080 LOG and CSR and SQI
F0F0 SQI
FAFA SQI or LOG
C0C0 SQI and CSR
F000 SQI and SIG
C000 SQI and SIG and CSR
FFF0 SQI or SIG
CCC0 (SQI or SIG) and CSR
A simple way to generate these values is to imagine four 16-bit quantities having the following
names and values: LOG=AAAA, CSR=CCCC, SQI=F0F0, SIG=FF00. The flag value needed
to represent a given logical combination of threshold outcomes is obtained as the result when
that same logical combination is applied to these special numbers.
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For example:
(SQI or SIG) and CSR = (F0F0 or FF00 ) and CCCC
= (FFF0) and CCCC
= CCC0
which corresponds with one of the examples given above.
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| | | | | | | | | | | | | | | | |
| Threshold Control Flags for Corrected Reflectivity | Input 12
|_______________________________________________________________|
See Description for Input #11.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Threshold Control Flags for Velocity | Input 13
|_______________________________________________________________|
See Description for Input #11.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Threshold Control Flags for Width | Input 14
|_______________________________________________________________|
See Description for Input #11.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Additive Offset for Measured AZ Angles (Binary Angle) | Input 15
|_______________________________________________________________|
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| | | | | | | | | | | | | | | | |
| Additive Offset for Measured EL Angles (Binary Angle) | Input 16
|_______________________________________________________________|
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| | | | | | | | | | | | | | | | |
| Intervening Gas Attenuation Correction (dB/km) | Input 17
|_______________________________________________________________|
Gas attenuation correction attempts to compensate for overall (two-way) beam losses due to
absorption by atmospheric gasses. The correction is linear with range, and is added to the data
along with range normalization. Therefore, clearing the RNV bit in Word #2 above disables the
correction. Of course, gas attenuation compensation can still be turned off even when RNV is
on, simply by setting a slope of 0.0 dB/km.
An attenuation of G db/km is encoded into the unsigned 16-bit word N as follows:
0 N 10000 G = N / 100000
else G = 0.1 + (N – 10000)/10000
This format is backward compatible with the previous linear format for all values between 0.0
and 0.1dB/km; but it extends the upper range of values from 0.65535 up to 5.6535. These larger
attenuation corrections are needed for very short wavelength radars.
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| | | | | | | | | | | | | | | | |
| Threshold Control Flags for Differential Reflectivity (Zdr) | Input 18
|_______________________________________________________________|
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See Description for Input #11.
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| | | | | | | | | | | | | | | | |
| Signed Zdr Calibration Offset in 1/16 dB (GDR) | Input 19
|_______________________________________________________________|
When differential reflectivity is computed there is a possibility that radar asymmetries will
introduce a bias in the Zdr values, i.e., that Zdr will be non-zero even when observing purely
spherical targets. This calibration offset permits nulling out this effect. The GDR offset
accounts for the overall Tx/Rx gain imbalance between the two channels of the radar.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Radar Wavelength in Thousandths of Centimeters | Input 20
|_______________________________________________________________|
The radar wavelength is used in the calculation of 16-bit velocity and width data, to convert
from Nyquist units to absolute physical units.
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| | | | | | | | | | | | | | | | |
| Signed LDR Calibration Offset in 1/100 dB (XDR) | XARG 1
|_______________________________________________________________|
The XDR offset is used in the Linear Depolarization Ratio equations, and is the differential
receiver gain between the two channels. Note that unlike the GDR offset (used for ZDR), the
gain difference does not depend on differential transmit power.
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| | | | | | | | | | | | | | | | |
| Range smoothing (0:None, 1:pairs, etc) | XARG 2
|_______________________________________________________________|
Range smoothing can be performed on raw moment data prior to the computation of scientific
parameters. The number of bins to sum together is given here. This should generally be an odd
integer so that no range bias is introduced by the smoothing operation.
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| | | | | | | | | | | | | | | | |
|Ena| | Point Clutter Thresh | Side Skip | XARG 3
|___|_______________________|_______________________|___________|
Point clutter detection is configured with this word. A bin will be flagged as containing clutter
if it’s power exceeds that of its two neighboring bins by more than the detection threshold (in
deciBels). Up to seven bins may optionally be skipped on each side of the central bin prior to
making these two comparisons.
Ena This bit is set to enable point clutter detection. Flag bits will then be reported in
the “Flg” output data type of the PROC command.
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| | | | | | | | | | | | | | | | |
|Ena|All| | XARG 4
|___|___|_______________________________________________________|
Point clutter censoring is configured with this word.
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Ena This is set to enable point clutter censoring. Raw moment data containing point
clutter will be interpolated from valid signal levels on either side.
All Optionally expand the reported detection flags to show the entire replaced interval,
not just the original detected bins. This gives a more honest view of the data bins
that have been altered.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Bit mask of TS playback mismatch conditions to ignore | XARG 5
|_______________________________________________________________|
This word is a combination of MMTS_xxx bits specifying what types of mismatches are okay
(do not cause an all-zero ray to be produced) during PROC command processing of timeseries
data that are played back from an external source into the RVP8.
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| | | | | | | | | | | | | | | | |
| Flag bits related to timeseries (playback) | XARG 6
|_______________________________________________________________|
Combination of OPTS_xxx bits which modify details of timeseries behavior.
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| | | | | | | | | | | | | | | | |
| 1 | Offset in deciBels | Slope as 100 * dB/dB | XARGs 7&8
|___|___________________________|_______________________________|
These two words allow you to set the breakpoints and slopes that modify the LOG threshold
according to the Clutter-to-Noise ratio of the target. This makes the LOG threshold behave
properly even as the noise floor becomes elevated due to very strong clutter targets. A value of
zero will restore the RVP8 defaults from the Mf menu.
The default (power-up) values for the above parameters are listed below. Both the scientific
units and the integer-input required by the command to set up that value are given. Most of
these defaults will likely be reasonable for a wide variety of radars.
Table 6–1:Default Values For Operating Parameters
Parameter
Sample Size 25 pulses 25
Flag Word 0007 Hex
Log Slope 0.03 dB/LSB 1966
LOG Threshold 0.5 dB 8
CCOR Threshold –25.0 dB –400
Signal Quality Index Threshold 0.5 (dimensionless) 128
SIG Threshold 10.0 dB 160
Calibration Reflectivity –22.0 dBZ –352
Scientific Units Input
Gas Attenuation 0.016 dB/km 1600
Zdr Offset (GDR) 0.0 dB 0
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Table 6–1:Default Values For Operating Parameters (cont.)
Parameter InputScientific Units
LDR Offset (XDR) 0.0 dB 0
AGC Integration Period 8 pulses 8
Radar Wavelength 5.3 cm. 5300
Dual PRF Filter Stabilization 10 pulses 10
UnCor Refl. Thresh. Control Flag LOG AAAA Hex
Cor Refl. Thresh. Control Flag LOG & CSR 8888 Hex
Velocity Thresh. Control Flag SQI & CSR C0C0 Hex
Width Thresh. Control Flag SQI & CSR & SIG C000 Hex
Zdr Refl. Thresh. Control Flag LOG AAAA Hex
AZ/EL Angle Offsets
0 degrees 0000 Hex
6.4 Interface Input/Output Test (IOTEST)
This command is used to test both the input and output data busses of the signal processor
interface. When issued, the command causes sixteen words to be read from the host controller,
after which those same sixteen words are written back out. Typically, the controller supplies a
“barber pole” input sequence consisting, for example, of successive powers of two. If all of the
output words are correct, one may conclude that there are no malfunctioning bits in the interface
hardware.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| | 0 0 0 1 1 | Command
|___________________________________________|___________________|
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| | | | | | | | | | | | | | | | |
| Arbitrary Data Word #1 Supplied by Host Controller | Input 1
|_______________________________________________________________|
.
.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Arbitrary Data Word #16 Supplied by Host Controller | Input 16
|_______________________________________________________________|
Host Computer Commands
Note: The IOTEST command can also process and echo up to 128 additional
XARGS data words (See Section 6.20).
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Copy of Data Word #1 as supplied by Host Controller | Output 1
|_______________________________________________________________|
.
.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Copy of Data Word #16 as supplied by Host Controller | Output 16
|_______________________________________________________________|
6.5 Interface Output Test (OTEST)
This command is used to test the integrity of the data being output by the signal processor. The
command causes sixteen words to be output consisting of successive powers of two starting from
one. By verifying whether each output word is correct, malfunctioning bits in the interface data
bus can easily be isolated. This test is less stringent than the input/output test IOTEST, since the
input data paths to the processor are not being checked. Typically, the OTEST is performed only
when the IOTEST fails, and then to determine whether the fault was on input or output.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| | 0 0 1 0 0 | Command
|___________________________________________|___________________|
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 | Output 1
|_______________________________________________________________|
.
.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 | Output 16
|_______________________________________________________________|
6.6 Sample Noise Level (SNOISE)
This command is used to estimate the current noise level from the receiver, so that the noise can
be subtracted from subsequent measurements. Data are sampled for 256 pulses at 256 bins,
beginning at a selectable range and spaced by the range resolution at that pulse width. The
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internal trigger generator is temporarily set to a special noise rate (usually much lower than the
operating rate) during the process. It is ultimately the user’s responsibility to insure that no
returned power is present within the approximately 32km sampling interval. In some cases it
may be necessary to raise the antenna during the noise measurement to avoid thermal noise
pickup from the ground, or from weather targets.
SNOISE has the option of setting up a new sampling range and trigger generator rate each time
it is called. Two bits in the command word determine which (if any) of the new values overrides
the current values stored in the RVP8. The power-up sampling range is 250km (input value of
250), and the power-up trigger rate is 200Hz (input value of 30000). These initial values persist
until such time as they are altered here. Note that both input words must always be supplied
after the command, even if the command calls for ignoring one or both of them. The range is
supplied directly in kilometers up to a maximum of 992km. The trigger rate resulting from a
given input is 6MHz divided by the input value, i.e. the input value is the trigger period in
0.1667 microsecond increments. Keep in mind that the given rate is bounded against the
minimum PRT allowed for the current radar pulse width.
The SNOISE command bounds the requested starting range of the noise sampling interval. This
is to insure that the noise samples will fit within the specified PRT, and within the range mask
hardware RAM. The RVP8 sets an error bit when an improper range is requested.
The SNOISE command should be re-issued now and then to compensate for drift in the RF and
A/D systems. However, because DC offsets do not propagate into the “I” and “Q” values,
reissuing the command is much less critical than with the RVP6. The noise levels must be
measured for the RVP8 to properly process data. This can be done by issuing the SNOISE at
least once after power-up, or by setting the correct values for the powerup noise levels with the
“mt” setup command, see section 3.2.5. The RVP8 does not automatically take a noise sample
as part of its initialization procedure.
The measured offsets are stored internally for all subsequent uses inside the RVP8. The offset
values may be inspected via the GPARM command, as may the current range and rate values
themselves. Of course, whenever the range or rate are changed the user must ensure that the
new trigger rate allows at least 32km following the new noise range. If this requirement is not
met, or if other failures are detected during the noise measurement, appropriate bits are set in the
GPARM latched status word. This word should generally be checked after SNOISE to make
sure that everything worked properly.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| |Action |Rat|Rng| | 0 0 1 0 1 | Command
|_______________|_______|___|___|___________|___________________|
Rng If 1, then the range in input word 1 is taken as the starting noise range for this and
all subsequent SNOISE calls.
Rat If 1, then the trigger rate in input word 2 is taken as the noise rate for this and all
subsequent SNOISE calls.
Action Specifies what action is carried out by the command.
0 Compute a new noise sample based on the present IFD input signals.
1 Do not compute a noise sample, but rather, read new noise values from the host
computer and use them for subsequent processing. Four additional input words
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supply the noise information, and GPARM words 6, 9, and 44-50 will be changed
to reflect the new noise settings.
2 Do not compute a noise sample, but rather, restore the powerup noise defaults.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Starting Range in km (Max 992km) of 32km Sampling Interval | Input 1
|_______________________________________________________________|
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Internal Trigger Rate (6Mhz/N) to use During Noise Sampling | Input 2
|_______________________________________________________________|
The following input words are optional, only if Action=1.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| 0 0 | (MSB) Log of Measured Noise Level (LSB) | Input 3
|_______|_______________________________________________________|
The is the same number as GPARM output 6. See the discussion in Sections 6.7 and 6.9.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Noise Level Standard Deviation (in 1/100 of a dB) | Input 4
|_______________________________________________________________|
This is the same number as the GPARM output 49.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| Ratio of Horizontal/Vertical Noise Power in Hundredths of dB | Input 5
|_______________________________________________________________|
This is the same number as the GPARM output 50.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| <Spare> |Err|Ttf|Ntg| Input 6
|___________________________________________________|___|___|___|
These fault bits will then be output in the latched status GPARM word 9 .
Ntg No Trigger during noise measurement.
Ttf Trigger too fast during noise measurement, i.e., some of the noise sample bins
were positioned past the trigger range.
Err Error detected during the SNOISE command.
6.7 Initiate Processing (PROC)
The PROC command controls the actual processing and output of radar data. The operating
modes and types of data available from the RVP8 are described in detail in Chapter 1. That
section also describes the proper use and application of the RVP8 to different radar
environments.
PROC is a single-word command that specifies the type of processing to be performed, and the
type of output to be generated. The two mode bits in the command word select either
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Synchronous mode — The processor acquires, processes, and outputs one ray in
response to each PROC command. Processing is begun only after each command is
actually received.
Free running mode — A single PROC command is issued and rays are continually output
as fast as they can be produced and consumed. This continues until any other command
is written, e.g., a NOP could be used to terminate the free running mode with no other
consequences.
Time Series mode — Always produced in a synchronous manner, this mode require a
new PROC command to initiate each new set of samples. Data are output as 8-bit time
series, 16-bit time series, or 16-bit power spectra.
Optional Dual-PRF velocity unfolding is chosen by command bits eight and nine. For Doppler
data either a 2:3, 3:4, or 4:5 PRF unfolding ratio may be selected. The RVP8 carries out all of
the unfolding steps internally, so that mean velocity is now output with respect to the larger
unambiguous interval. There is no additional velocity processing needed by the user, except of
course, to change the velocity scale on any displays being generated. Furthermore, spectral
widths are scaled consistently with respect to the higher PRF, and require no user modification
before being plotted.
When unfolding is selected, the internal trigger generator automatically switches rates on
alternate rays. The switch over occurs immediately after the last pulse of the current ray has
been acquired; thus overlapping the internal post-processing and output time, with transmitter
stabilization and data acquisition at the new rate.
Output data are selected by the upper six bits of the PROC command. Packed archive output is
selected by setting the ARC bit. Individual byte or word display output is selected by setting any
or all of the Z, T, V, W, Zdr, and KDP command word bits. When more than one of these bits is
set, the output array consists of all of the bins for the leftmost selected parameter, followed by all
of the bins for the next selected parameter, etc. Bits selected in XARG #1 behave the same way,
except that the output order is right-to-left. Both archive and display formats can be selected
simultaneously, in which case the archive format is output first, followed by whichever
individual display format values were also selected. The archive format is not recommended for
use with new drivers because it can only handle four of the many possible output parameter
types.
When time series mode is selected there are three output data formats available. For backwards
compatibility, there is an 8-bit integer format in which the eight most significant bits from the I,
Q, and LOG signals are represented in a byte. This format is not recommended because it will
generally miss weak signals. We recommend the floating-point format that uses 16-bits per A/D
sample. There is also a 16-bit power spectrum output that is accurate to 0.01dB. (See also
GPARM output word #10).
In addition to the above output data, the first words of each ray optionally contain additional
information about the ray itself. These header words are configured by the CFGHDR opcode,
and are included only if the NHD (No-Headers) bit in SOPRM Input #2 is clear. For example, if
TAG angle headers are requested, if the ARC, Z and V bits are all set, and if there are 100 bins
selected in the current range mask, then each RVP8 output ray consists of the following:
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1] TAG15 – TAG0 \ From Start of Acquisition
2] TAG31 – TAG16 / Interval
3] TAG15 – TAG0 \ From End of Acquisition
4] TAG31 – TAG16 / Interval
* 200 words of packed archive data,
* 100 words of Corrected Reflectivity data in low byte only.
* 100 words of Velocity data in low byte only,
Host Computer Commands
The Command word format for Synchronous Doppler Mode is:
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
|ARC| Z | T | V | W |ZDR|Unfold |KDP| 0 1 | 0 0 1 1 0 | Command
|___|___|___|___|___|___|_______|___|_______|___________________|
The Command word format for Free Running Doppler Mode is:
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
|ARC| Z | T | V | W |ZDR|Unfold |KDP| 1 0 | 0 0 1 1 0 | Command
|___|___|___|___|___|___|_______|___|_______|___________________|
Either of these may be augmented by an optional XARG word (See Section 6.20)
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | (Tx Vert) | (Tx Horz) | | | |
| |Flg|Phi Rho Ldr|Phi Rho Ldr|SQI|RHV|PDP| XARG 1
|_______________________|___|___|___|___|___|___|___|___|___|___|
Unfold Selects Dual–PRF unfolding scheme:
00 : No Unfolding 01 : Ratio of 2:3
10 : Ratio of 3:4 11 : Ratio of 4:5
ARC Selects archive output format in which four data bytes (see 8-Bit descriptions be-
low) are packed into two output words per bin as follows:
High Byte Low Byte
| | |
| V | Z | First Word
|___________|___________|
_______________________
| | |
| W | T | Second Word
|___________|___________|
The remaining data parameters are available in both 8-Bit and 16-bit formats, according to
SOPRM Command input word #2 (See Section 6.3). The same SOPRM word configures the
RVP8 for Single or Dual polarization. The later is required for KDP, PDP, and RHV to be
computed properly.
V Selects radial velocity data.
8-Bit Velocity Format
— Mean velocity, expressed as a fraction of the unambig-
uous velocity interval, is computed from the unsigned byte N as:
V
m/sec =VNyquist
x (N–128) / 127.5
0 : Indicates velocity data is not available at this range
1 : Maximum velocity towards the radar
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When velocity unfolding is selected, the output is still interpreted as above, except that the unambiguous interval is increased by factors of 2, 3, and 4 for for
2:3, 3:4, and 4:5 unfolding.
Host Computer Commands
128 : Zero velocity
255 : Maximum velocity away from the radar
16-Bit Velocity Format
— Mean velocity in meters/second is computed from the
unsigned word N as:
V
m/sec
The overall range is from –327.67m/sec to +327.66m/sec in one centimeter/second steps as follows:
0 : Indicates velocity data is not available at this range
1 : –327.67 m/sec (towards the radar)
32768 : 0.00 m/sec
65534 : +327.66 m/sec (away from the radar)
65535 : Reserved Code
W Selects spectral width data.
8-Bit Width Format
—Spectral width is computed from the unsigned byte N as:
W
The overall range is a fraction between 1/256 to 255/256 of the unambiguous interval. The code of zero indicates that width data was not available at this range.
16-Bit Width Format
— Spectral width in meters/second is computed from the
unsigned word N as:
W
The overall range is from 0.01m/sec to 655.34m/sec in one centimeter/second
steps as follows:
0 : Indicates width data is not available at this range
1 : 0.01 m/sec
65534 : 655.34 m/sec
65535 : Reserved Code
= (N–32768) / 100
m/sec
= N / 256
= N / 100
Nyquist
Z Selects clutter corrected reflectivity data.
8-Bit deciBel Format
— The level in decibels is computed from the unsigned
byte N as:
dBZ = (N–64)/2.
The overall range is therefore from –31.5 dBZ to +95.5 dBZ in half-dB steps as
follows:
0 : Indicates no reflectivity data available at this range
1 : –31.5 dBZ
64 : 0.0 dBZ
128 : 32.0 dBZ
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255 : +95.5 dBZ
16-Bit deciBel Format
— The level in decibels is computed from the unsigned
word N as:
dBZ = (N–32768) / 100
The overall range is from –327.67dB to +327.66dB in 1/100dB steps as follows:
0 : Indicates no reflectivity data available at this range
1 : –327.67 dBZ
32768 : 0.00 dBZ
65534 : +327.66 dBZ
65535 : Reserved Code
T Selects total reflectivity. Same 8-bit and 16-bit coding formats as for clutter cor-
rected reflectivity above.
ZDR Selects differential reflectivity data.
8-Bit ZDR Format
— The level in decibels is computed from the unsigned byte
N as:
dB = (N–128) / 16
The overall range is from –7.935dB to +7.935dB in one-sixteenth dB steps as follows:
0 : Indicates no reflectivity data available at this range
1 : –7.9375 dB
128 : 0.0000 dB
255 : +7.9375 dB
16-Bit ZDR Format
— Same as 16-bit deciBel format.
KDP Selects dual polarization specific differential phase data.
8-Bit KDP Format
— Values are coded into an unsigned byte using a logarithmic scale. The KDP angles are multiplied by the wavelength in cm. (to reduce
dynamic range) and then converted to a log scale separately for both signs. The
minimum value is 0.25 deg*cm/km, and the maximum value is 150.0 deg*cm/
km. A code of zero represents no data, and a code of 128 represents 0 deg*cm/
km. The conversion equation for positive values (codes from 129 to 255) is:
N*129
ƪ
ƫ
KDP l + 0.25 600
126
The conversion equation for negative values (codes from 1 to 127) is:
127*N
ƪ
ƫ
KDP l + –0.25 600
126
16-Bit KDP Format — Same as 16-bit deciBel format, except that the units are
hundredths of degrees per kilometer. No weighting by wavelength is introduced.
F
PDP Selects dual polarization differential phase
6–18
data.
DP
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