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11/18/02 Technical Interchange Meeting
Progress in FY-02
• Research RDA– Capability to collect time series data– Control of phase shifter
• Phase coding– Sigmet’s implementation of SZ algorithm
– Ground clutter filtering if P1 < P2
– Collected sample time series of SZ coded data
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11/18/02 Technical Interchange Meeting
Research RDA Status
• Operational in legacy and RRDA mode• Both modes accommodate RVP-7 in
parallel• RVP-7 used for JPOL demo• Plan to integrate RVP-8 ASAP
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11/18/02 Technical Interchange Meeting
RRDA Status• Full control of radar• Integrated with ORPG• Phase shifter control• Versatile VCP structures and tools• Real-time displays• VCP 43 & 44 implemented, data to
ROC• Real-time phase coded acquisition
with first trip decoding
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11/18/02 Technical Interchange Meeting
RRDA Status• Staggered PRT capability implemented• Working on real-time software for
staggered PRT• Continuous archive level 1 and 2 for
several hours• Real-time playback of archive data• Data storage in compressed native
format• Matlab format and ingest into Matlab• Recording on tape, CD, and/or DVD
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11/18/02 Technical Interchange Meeting
SZ Decoding Algorithms
• Analysis of Sigmet’s SZ decoding algorithm– Sigmet provided internal notes on decoding
algorithm
• Comparison with NSSL’s SZ-1 decoding algorithm– Major difference is in the substitution
method
• MATLAB simulations to compare performance
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11/18/02 Technical Interchange Meeting
0 10 20 30 40 50 60 70-8
-6
-4
-2
0
2
4
6
8
p1/p
2 (dB)
err
or
in v
2 est
ima
te (
m s
-1)
(v1-v
2)=-28 to 28 m s-1, w
1=4 m s-1;w
2=4 m s-1
SZ(8/64) code, va=32 m s-1, n
w=0.75, von Hann window
--- mean; ___sd., substitution (Siggia's method)
Sigmet’s Implementation
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11/18/02 Technical Interchange Meeting
SZ-1 algorithm
0 10 20 30 40 50 60 70-8
-6
-4
-2
0
2
4
6
8
p1/p
2 (dB)
err
or
in v
2 est
ima
te (
m s
-1)
(v1-v
2)=-28 to 28 m s-1, w
1=4 m s-1;w
2=4 m s-1
SZ(8/64) code, va=32 m s-1, n
w=0.75, von Hann window
--- mean; ___sd., SZ-1 method
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11/18/02 Technical Interchange Meeting
0 10 20 30 40 50 60 700
1
2
3
4
5
6
p1/p2 (dB)
sd(v
2) m
s-1
smoothed sd(v2), w
1=4 m s-1, (v
1-v
2)= -28 to +28 m s-1
w2=2 m s-1
w2=4 m s-1
w2=6 m s-1
w2=8 m s-1
2
4
6
8
=10 cm, PRT=0.7812 ms, va=32 m s-1, SZ(8/64) code
SZ-1 methodsubstitution (Siggia's method)
SD(v) for the two methods
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11/18/02 Technical Interchange Meeting
SD(σv) for the two methods
0 10 20 30 40 50 60 700
0.5
1
1.5
2
2.5
3
3.5
4
p1/p2 (dB)
sd(w
2) m
s-1
smoothed sd(w2), w
1=4 m s-1, (v
1-v
2)= -28 to +28 m s-1
w2=2 m s-1
w2=4 m s-1
w2=6 m s-1
w2=8 m s-1
2
4
6
8
=10 cm, PRT=0.7812 ms, va=32 m s-1, SZ(8/64) code
deconvolution methodsubstitution (Siggia's method)
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11/18/02 Technical Interchange Meeting
Bias in σv for the two methods
0 10 20 30 40 50 60 70-6
-5
-4
-3
-2
-1
0
1
2
3
4
p1/p2 (dB)
me
an
err
or
in w
2 est
ima
te (
m s
-1)
smoothed sd(w2), w
1=4 m s-1, (v
1-v
2)= -28 to +28 m s-1
w2=2 m s-1
w2=4 m s-1
w2=6 m s-1
w2=8 m s-1
2
4
6
8
=10 cm, PRT=0.7812 ms, va=32 m s-1, SZ(8/64) code
deconvolution methodsubstitution (Siggia's method)
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11/18/02 Technical Interchange Meeting
Comparison of Random Phase and SZ code – Lincoln Labs
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11/18/02 Technical Interchange Meeting
GCF and Phase Coding
• Optimum ground clutter filter– Frequency response– Notch width
• Ground clutter filtering if P2 > P1
– Sigmet reverts to random phase processing
– SZ algorithm was modified to address this problem
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11/18/02 Technical Interchange Meeting
Optimum Clutter Filter
S(v) + NC(v) + N
Noise level: N
N1
v
v
C(v) + N1
GCF(v)
Input
Output
Normalized noise level: 1
v
S(v) + NN
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11/18/02 Technical Interchange Meeting
Effects of the number of samples
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11/18/02 Technical Interchange Meeting
Optimum filter width
0 0.5 1 1.50
1
2
3
4
5
6
clutter width, c (m s-1)
clu
tter
filte
r h
alf
wid
th,
wcf
/2 (
m s
-1)
CNR= 60
dB
50 dB
40 dB
30 dB
20 dB
10 dB
1.3
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11/18/02 Technical Interchange Meeting
Clutter filtering if Pc>P2>P1
1. Re-cohere 1st trip and filter ground clutter
2. Restore lost spectral coefficients of 2nd trip replicas
3. Re-cohere 2nd trip, obtain moments, and filter 2nd trip signal
4. Re-cohere 1st trip and obtain moments
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11/18/02 Technical Interchange Meeting
Restoration of lost 2nd trip spectrum replica
1. Use the remaining replicas to determine the magnitude and phase – similar to substitution and works at narrow
widths
2. Reconstruction of magnitudes and phases in case there is only one overlap of the spectral replicas – extends the range of spectrum widths – requires solution of linear equations
(overdetermined system)
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11/18/02 Technical Interchange Meeting
GCF effect on 2nd trip spectrum replicas
20 40 60 80 100 120 140 1600
2
4
6
8
10
a
b
so(i)
ma
gn
itud
espectrum of 2nd trip echo
va=32 m s-1, v=-22 m s-1, w=2 m s-1, M=160
20 40 60 80 100 120 140 1600
1
2
3
4
5
s(k)
ma
gn
itud
e
SZ(8/64) phase coded spectrum
GCF GCF
8
1
2
3
4
5
6
7
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11/18/02 Technical Interchange Meeting
P2/P1 Ratio for which spectral moments of 1st trip can be recovered
0 1 2 3 4 5 60
10
20
30
40
50
60
spectrum width, w2 (m s-1)
ove
rlay
po
we
r ra
tio, p
2/ p1 (
dB
)w
1=4m s-1, SNR
1=20dB, CNR=70dB
va=32m s-1, w
c=0.28m s-1, M=64, n
c=15
performance of the 2nd trip signal restoration schemes -1 & 2
(a)
(b)
(c)
(a) - no restoration(b) - scheme-1(c) - scheme-2
p1
v1
w1
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11/18/02 Technical Interchange Meeting
Data Collection
• Volume Coverage Pattern Definitions– ROC requested non-standard VCPs– Modified RRDA VCP definitions to accommodate
new requirements• Automatic switch between phase-coded and non-
phase-coded elevation cuts• Staggered PRT
• Level-1 Data Archiving– Expanded data headers to include new metadata– Currently support MATLAB and RRDA internal
formats
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11/18/02 Technical Interchange Meeting
Collection of SZ coded data
Reflectivity field
PRT #1T = 3.1 msra = 466 km
vNYQ = 8.92 m s-1
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11/18/02 Technical Interchange Meeting
Collection of SZ coded data
Doppler velocity field
PRT #1T = 3.1 msra = 466 km
vNYQ = 9 m s-1
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11/18/02 Technical Interchange Meeting
Real-time decoding of 1st trip
PRT #4 (T = 1.17 ms)ra = 175 km
vNYQ = 24 m s-1
PRT #8 (T = 0.78 ms)ra = 117 km
vNYQ = 35 m s-1
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11/18/02 Technical Interchange Meeting
Plans
• Real-time implementation of SZ
algorithm
• Real-time implementation of
Staggered PRT
• SPS Simulator
• Oversampling and Whitening in range
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11/18/02 Technical Interchange Meeting
SPS Simulator
• R/V algorithms require development at the RDA DSP level – Rapid algorithm prototyping and validation– Data visualization tools– Off-line development using Archive 1 data
• Working on simulation of RRDA DSP (Legacy WSR-88D HSP/PSP) using MATLAB– Capability to simulate RVP-8
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11/18/02 Technical Interchange Meeting
Plans for the SPS Simulator
• Data Analysis– Spectral analysis
• Data Processing– R/V ambiguitiy mitigation
• Phase coding • Staggered PRT
– Interaction with other techniques• Oversampling and whitening in range
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11/18/02 Technical Interchange Meeting
Oversampling of Weather Echoes in Range
L samples within the pulse
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11/18/02 Technical Interchange Meeting
Whitening-Transformation-Based Estimates
• Oversample in range by a factor of L– Range samples are correlated– Correlation is known assuming uniform reflectivity
• Decorrelate oversampled range data– Whitening transformation is derived from “known” C– Works for SNR > 15 dB
• Compute autocovariances for each range gate• Average autocovariances from L range gates
– Statistical errors are reduced
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11/18/02 Technical Interchange Meeting
Reduction in statistical errors by processing oversampled signals in range
PRT = 3 ms M = 32 L = 9
NEXRAD specification
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11/18/02 Technical Interchange Meeting
Plans for Oversampling and Whitening in Range
• Collection of oversampled data with RRDA– Long pulse, L = 3– Digital receiver, L ≥ 5– Examine RVP-8 capabilities
• Statistical analysis– Matched filter, Regular averaging, Whitening
• Visual comparison of PPI displays • Effects of reflectivity gradients• Pseudo-whitening techniques