Post on 15-Jul-2015
Evaluation of Calibration Accuracy with HPS Evaluation of Calibration Accuracy with HPS (HongIk Polarimetric Scatterometer)(HongIk Polarimetric Scatterometer)
System for Multi-Bands & Multi-PolarizationsSystem for Multi-Bands & Multi-Polarizations
Ji-Hwan Hwang*, Soon-Gu Kwon, and Yisok OhElectronic Information and Communication Eng., HongIk University
Ji-hwan_hwang@mail.hongik.ac.kr; yisokoh@hongik.ac.kr
Contents 1) Objectives 2) Configuration of HPS system 3) Innovative antenna system for L-band 4) System calibration & accuracy evaluation 5) concluding remarks
1
Objec tivesObjec tives
• For a comparison study on earth observation with satellite SAR system at various frequency bands, requirements of multi-bands / polarizations ground based scatterometer continuously are increasing.
• the existing HPS(Hongik Polarimetric Scatterometer) system basically support L-,C-,X-bands and full-polarizations (vv-, vh-, hv-, hh-pol.), however, those are separated system.
• this study shows configurations of 1)integrated system for multi-bands with single platform and evaluates an accuracy of 2)system calibration in the field experiments.
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3IG ARS S 2011
C onfiguration of HPS s ys temC onfiguration of HPS s ys tem
1) Boom structure (8m) : movable platform 2) Head part : it’s consist of sensor (OMT+Ant.) and
incident angle control
3) Sub-circuit : this circuit achieves two functions of
frequency converting and switching for full-polarization
4) DAQ, Graphic User Interface : HPS is basically network analyzer
based system, Agilent 8753E and controlled by GUI
[1] P. O’Neill, et al, “Survey of L-Band Tower and Airborne Sensor System Relevant to Upcoming Soil Moisture Missions,” IEEE Newsletter Geosci. Remote Sensing, Jun. 2009.
4
• To implement the motion control(θ,Ф), head part is composed of 3
step motors and inclinometer sensor. Incident angle (θ) : tolerance 0.2°
IG ARS S 2011
C onfiguration : Head Part C onfiguration : Head Part
(2) Inclinometer sensor (2-axis)
(1) Step motors
(3ea)
MOVE Ang.(Amove=An-Ain)
Meas. Ang. (A(n+1))
Input Inc.angle (Ain)
No
YesSet position (destination)
Meas. Curr. Ang.
(An), n=0
(n+1)
Meas. Ang. (An), n=1
Amove
[2] J.-H. Hwang, S.-M. Park, S.-G. Kwon, Y. Oh, “Study on the calibration of a full-polarimetric scatterometer system at X- band (in Korean)”, KIEES, Apr. 2010.
5
• Switching circuit offers full-polarimetric signal without mode change of network
analyzer (Agilent 8753E) and switch the path for each bands• Frequency conversion and amplifier circuit only for X-band minimize signal
distortion and path loss through 7m RF cable : (9.65GHz to 1.25GHz, gain 32dB
p1dB 20dBm)
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C onfiguration : s ub- c irc uitC onfiguration : s ub- c irc uit
RF-cable 7m
Pol. indicator
H-pol.V-pol.
P1P2
Circ#1
Circ#2
SW#1
J1
J2
SW#2
J1
J2
8.4GHz
1 1 .5d Bm
+ 1 2V
+ 1 2
V
+ 1 2V
M IXTX
M IXRX
D IV
ISO TX
ISO RX
BPF PA
LNA
LO
•Freq. Conversion (X-band) •Pol. Selection
Bypass for L- & C-bands
SW#3
J2
J1
SW#4
J1
J2
SW#5
J2
J1
SW#6
J2
J1
Network analyzer
Antenna + OMT
Tx-path
Rx-path
6IG ARS S 2011
• GUI software controls whole measurement system:
ex) inc. angle, time gating, Tx power level, automatic meas., system cal.
C onfiguration : G UI & DAQ C onfiguration : G UI & DAQ
File header
Full-pol. Measurement data
Incidence angle
7IG ARS S 2011
Innovative Ant. S ys tem for L- band Innovative Ant. S ys tem for L- band ( type 1)( type 1)
• the existing ant. system (horn ant. + OMT) for L-band is too bulky to be installed in HPS platform. So, we suggested two types of compact OMT.
[3] J. -H. Hwang, S.G. Kwon, Y. Oh, “orthomode transducer using trapezoidal waveguide”, Patent in Korea, 10-2010-0090749 (in progress).
Waveguide taper
waveguideT-junctionV-pol.
H-pol.
Common mode port
< Commercial class 1 OMT >
Waveguide taperV-pol.
H-pol.Conducting
post
Total length =75cm,
< OMT with Compact T-junction>
Reduced total size to about 56%
• Type 1 OMT is minimized by newly designed compact T-junction
8IG ARS S 2011
Innovative Ant. S ys tem for L- band Innovative Ant. S ys tem for L- band ( type 2)( type 2)
• Total length of new OMT is about 86cm (commercial OMT 1.35m)• It achieved reducing the OMT size to about 62% and also keeping the comparable performance with the same class OMT structure
Stepped-horn antenna(length: 300mm, 1.26λ 0
aperture: 450×450mm2)
Proposed new OMT(length: 560mm, 2.35λ 0)
[4] J. -H. Hwang, Y. Oh, “Compact OMT Using Single-Ridged Triangular Waveguide”, IEEE MWCL, 2011.[5] J. -H. Hwang, S.G. Kwon, Y. Oh, “orthomode transducer using waveguide with 4-splitted triangular cross section”, Patent in Korea, 10-2010-0091816 (in progress).
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S ys tem c alibration ( S ing le Target C al. S ys tem c alibration ( S ing le Target C al. Tec h. )Tec h. )
IG ARS S 2011
[5] K. Sarabandi, and F. T. Ulaby, “A convenient technique for polarimetric calibration of single-antenna radar systems,” IEEE Trans. Geosci. Remote Sensing, Nov. 1990.
IG ARS S 2011
• HPS system was calibrated using STCT at each frequency bands.• to calibrate HPS system, measured data of ref. and test targets are needed,
and we can calculate the calibrated scattering matrix of test target.
( )( )
( )( )
( )( )
2 2 2 012 21 11 222 0 0 0 02
12 21 11 22
2 2 2 012 21 22 112 0 0 0 02
12 21 22 11
2 2 212 21 11 222 0 0 02
12 21 11
12 1
1
12 1
1
2 2 11
u u u u
vv
u u u u
hh
u u u
vh
m m m ms C C C s
m m m mC
m m m ms C C C s
m m m mC
m m m mCs C C C
m m mC
= − + + − +
−
= − + + − +
−
= + − − +−
( )( )
( )
0022
2 2 2 021 12 11 222 0 0 0 02
21 12 11 22
0 012 210 011 22
2 2 11
1 , 1 1
u
u u u u
hv
sm
m m m mCs C C C s
m m m mC
m ma C a
m m a
= + − − +
−
→ = = ± − −
s0 : theoretical [S0] of ref. target (sphere)
m0 : measured [M0] of ref. target (sphere)
mu : measured [Mu] of test target (C.R.)
spg : calibrated [S] of test target (C.R.)
Mie exact solution
2DTST (2D target scanning technique)
This method offers ‘well-aligned’ data
1 0IG ARS S 2011
S ys tem c alibration ( 2D Target S c anning S ys tem c alibration ( 2D Target S c anning Tec h. )Tec h. )
• 2DTST: this technique can measure full-pol. freq. responses of ref. / test
targets and graphically choose the ‘well-aligned’ center data.
[4] J. -H. Hwang, S. -M. Park, Y. Oh, “Calibration Accuracy Enhancement in the Field Experiment with a Ground-Based Scatterometer”, IGARSS 2010, Aug. 2010.
• Concept view of gird system for 2DTST
-100
10
-100
10-40
-20
0
ζ [deg]ψ [deg]Nor
m. P
atte
rn V
V-p
ol [d
B]
-100
10
-100
10-40
-20
0
ζ [deg]ψ [deg]Nor
m. P
atte
rn H
H-p
ol [d
B]
-100
10
-100
10-100
0
100
ζ [deg]ψ [deg]Pha
se d
iffer
ence
, φhh
- φvv
[deg
]
-100
10
-100
10-100
0
100
ζ [deg]ψ [deg]Pha
se d
iffer
ence
, φvh
- φvv
[deg
]
Max point (-1,1) ~ boresight
Scan resolution ~1˚
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S ys tem c alibration ( multi- bands /full-S ys tem c alibration ( multi- bands /full-pol. )pol. )
1 1
• These results are calibrated Full-pol. freq. responses using STCT and 2DTST• to evaluate calibration accuracy, conducting sphere of 30cm diameter and
30/45cm TCR were used as REF. and test target, respectively.
9.4 9.5 9.6 9.7 9.8 9.9-40
-30
-20
-10
0
10
freq. [GHz]
X-Band
5.1 5.2 5.3 5.4 5.5-40
-30
-20
-10
0
10
freq. [GHz]
C-Band
1 1.1 1.2 1.3 1.4 1.5-40
-30
-20
-10
0
10
freq. [GHz]
RC
S, σ
pq [d
Bsm
]
L-Band
theoryun-cal. cal.s
vvs
vhs
hvs
hh
After calibration, effective isolation levels improve more than about 10dB
9.4 9.5 9.6 9.7 9.8 9.9-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
freq. [GHz]
5.1 5.2 5.3 5.4 5.5-1.5
-1
-0.5
0
0.5
1
freq. [GHz]
1 1.1 1.2 1.3 1.4 1.5-6
-5
-4
-3
-2
-1
0
1
freq. [GHz]
Ras
idua
ls [d
B]
X-BandC-BandL-Band
IG ARS S 2011 1 2
Cal. resid.un-cal. resid.
Cal. accuracy~ 0.3dB
~ 0.4dB
~ 0.3dB
• Calibration accuracy can be defined to RMS value of the norm of residuals,
which is a degree of similarity between two data arrays.
: : ..
#of data points
pq theory pq measnorm M MCal accuracy
−= : RMS norm of residuals
E valuation of C al. ac c urac yE valuation of C al. ac c urac y
1 3IG ARS S 2011
E valuation of C al. ac c urac yE valuation of C al. ac c urac y
• These results show the spatial changes of calibration accuracy
depending on the degree of mis-alignment between antenna and test target.• we can assign ‘Reliability zone’, which is ‘well-aligned’ region to
guarantee the calibration accuracy of 0.5dB in field experiments.
0 5 10 15 20 25 300
10
20
30
40
50
60
Off-Center Angle [deg]
Cal
.Err
or: m
ag [d
B]
σvv: [dB]
σhh: [dB]
φhh-φvv: [deg]
10
20
30
40
50
60
0 5 10 15 20 25 300
10
20
30
40
50
60
Off-Center Angle [deg]
σvv: [dB]
σhh: [dB]
φh
10
20
30
40
50
60
h-φvv: [deg]
0 5 10 150
10
20
30
40
50
60
Off-Center Angle [deg]
σvv: [dB]
σhh: [dB]
φhh-φvv: [deg]
Ph
ase
erro
r [de
g]10
20
30
40
50
60
X-Band C-Band L-Band
Reliability zone ~ 6.5° ~ 5° ~ 3°
*Note: It depends on meas. antenna radiation pattern: HPBW (29°/35°, 25°/29°, 12°/13°), E-/H-. Phase error does not exceed about 7˚ in all frequency bands.
1 4IG ARS S 2011
• HPS system for multi-bands & multi-polarizations integrated to single-platform and, especially, the newly designed antenna + OMTsystem for L-band is applied. • To calibrate scatterometer system, STCT and automatic 2DTSTwere used, and these results agreed well with theoretical RCS.
• ‘Reliability Zone’, to guarantee 0.5dB calibration accuracy, are 6.5˚, 5˚, and 3˚ in L-,C-,X-bands, respectively.
• This ground-based HPS system will be continuously used for comparison study of satellite SAR system as a test-bed.
C onc luding remarksC onc luding remarks
Thanks, do you have any questions??
1 5IG ARS S 2011
Appendix 1. ( off- c enter error rate )Appendix 1. ( off- c enter error rate )
0 10 20 30 400
20
40
60
80
100
Off-Center Angle [deg]
Err
or r
ate
[%]
Threshold of 5% error rate~3°
# of samples = 441eaAVG: full-pol.
• to verify the off-center error caused by mis-alignment, we measured
surroundings from the center of ref. target. • we assume that the well-aligned center data, maximum position between
antenna and target, have highest accuracy and reliability.
Error rate (1 .) 100 (%)corr= − ×
where,
‘corr.’ is correlation coefficient of
centered and off-centered meas.
data arrays of ref. target.
< e.g., Off-center errors of X-band >
1 6IG ARS S 2011
Appendix 2. Appendix 2. : Bac ks ac ttering c oef. (: Bac ks ac ttering c oef. ( σσ ) in tidal flat + pattern ˚) in tidal flat + pattern ˚c al.c a l. [ M [ M00 ]]
C-band, 2010.08.16
10 20 30 40 50 60 70-40
-30
-20
-10
0
10
Incidance angle [deg]
σ0 pq [d
B]
oysterC1
6Aug2010.txt
σ0vv
σ0vh
σ0hv
σ0hh
10 20 30 40 50 60 70-40
-30
-20
-10
0
10
Incidance angle [deg]
σ0 pq [d
B]
mudC1
6Aug2010.txt
σ0vv
σ0vh
σ0hv
σ0hh
Oyster field Mud area
10 20 30 40 50 60 70-40
-30
-20
-10
0
10
Incidance angle [deg]
σ0 pq [d
B]
oysterX1
7Aug2010.txt
σ0vv
σ0vh
σ0hv
σ0hh
10 20 30 40 50 60 70-40
-30
-20
-10
0
10
Incidance angle [deg]
σ0 pq [d
B]
mudX1
7Aug2010.txt
σ0vv
σ0vh
σ0hv
σ0hh
C-band: oyster field
X-band: mud areaX-band, 2010.08.17
Oyster field Mud area