© UPC IGARSS 2011 Vancouver 24-29 July 2011 1 / 13
First results of the PAU Synthetic First results of the PAU Synthetic Aperture RadiometerAperture Radiometer
I. Ramos-Perez, G. Forte. X. Bosch-Lluis, E. Valencia,
N. Rodriguez-Alvarez, H. Park, M. Vall·llossera, and A. Camps
E-mail: [email protected]
Remote Sensing Lab
Universitat Politècnica de Catalunya (UPC) – Barcelona, Spain
and IEEC-CRAE/UPC
28th of July of 2011
© UPC IGARSS 2011 Vancouver 24-29 July 2011 2 / 13
Outline
1. Review of PAU-SA instrument 2. Potential improvements for future SMOS – like missions3. Use of PRN Signals for: Calibration, FWF Determination, and
receiver’s frequency response determination
4. Inter-calibration phase determination in post-processing and real-time systems
5. Some Imaging results:
Impulse response (near field) Angular resolution (near field) GPS satellites constellation
6. Conclusions
© UPC IGARSS 2011 Vancouver 24-29 July 2011 3 / 13
1. PAU-SA Instrument
h,v sea surface roughness SST, , T , ( SSS)
PAU-SA in the robotic arm
PAU-RAD
PAU-GNSS-R
PAU-IR
8 m
© UPC IGARSS 2011 Vancouver 24-29 July 2011 4 / 13
Parameter MIRAS/SMOS PAU-SA Comments
Frequency operation L-band (1400 - 1427 MHz)L-band (1575.42 MHz)
L1 of GPS signal
Same frequency both Radiometry and GPS Reflectrometry
Bandwidth 19 MHz 2.2 MHz Spatial correlation effects negligibleLarger TArm size 4 m 1.3 m
Altitude Global observation, LEO, orbital altitude ground-based -
Antenna typePatch antenna with V & H polarizations
(not simultaneous)Patch antenna with V & H polarizations
(simultaneous)
Full-pol(non-sequential)
Number of antennas per arm 23 8+1 (dummy) Improve antenna pattern similarity
Number total antennas 69 31 -
Antenna spacing0.875 at 1400 MHz,
(21 cm) 0.816 at 1575.42 MHz,
(15.5 cm) Increase the alias-free field of view
Receiver typesingle polarization (1 per element)
dual polarization(2 per element)
Full-pol(non-sequential)
Topology of the LO down-converter
Distributed LO (groups of 6 elements)
Centralized reference clock + internal LO generated in each receiver
Reduce LO leakage and
correlated offset
Quantization1 bit
(Inside the LICEF )8 bits IF sub-sampling using a external ADC
Digital I/Q demodulationDigital Power measurement
Digital LPF I/Q conversion Analog Digital Elimination quadrature error
Frequency response shaped by
Analog RF filter Digital low- pass filterMass reduction, quasi perfect matching, no temperature and
aging drifts Power measurement system
(PMS)Analog (Schottky diode) Digital (FPGA)
Mass reduction, Thermal drifts minimized
Calibration by Noise Injection
Injection of Distributed noiseInjection of Centralized noise
or PRN signal
Simpler calibration.Calibration of non-separable errors
Recs’ freq. response estimation
Image capabilities Dual-pol or full-pol (sequential) Full-pol (non-sequential) Necessary to GNSS-R applications
2. Potential improvements for future SMOS’s
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3.1. Use of PRN Signals for: FWF determination
PRNSRB
B
chips
PRNPRN
NB
FWF(Y1Y2)
• Overcomes limitations of centralized noise injection• PRN with SR > 5 (flat spectrum such as Noise Source)• Estimation of FWF at =0 with 1B/2L
• Amplitude error < 0.25%• Phase error < 1º
Centralized Calibration using:Noise Source or PRN sequences
SR=0.5
SR=1
SR=5 I. Ramos-Pérez et al., “Use of Pseudo-Random Noise sequences in microwave radiometer calibration”, MICRORAD 2008 I. Ramos-Pérez et al., “Calibration of Correlation Radiometers Using Pseudo-Random Noise Signals” Sensors 2009 ISSN 1424-8220
© UPC IGARSS 2011 Vancouver 24-29 July 2011 6 / 13
A
SPRN+SR2
SPRN+SR1
3.2. Use of PRN Signals for: Receiver’s frequency response
Correlation of receivers’ output with local replica of PRN signal injected allows individual frequency responses to be measured (amplitude and phase)
*
* * *
2 *
m mˆ
n n n n
k
ˆ
ˆ
k
mi ixy xyDFT DFT x DFT y
DFT PRN DFT PRN DFT n DFT h
DFT PRN H
R r
1
1m n n m
i
N
in
xyr x yN
*
2
kk i
ixyH
DFT PRN
R
Using: PRN sequences
© UPC IGARSS 2011 Vancouver 24-29 July 2011 7 / 13
4.1. Inter-calibration time in real-time systems
Data: PAU-SA instrument
Measurement: τ =1 s., every 2 min Off-line Processing Decimate to simulate lack of data
Best interpolation Methods:• Linear• Pchip• Spline• fft
INTERPOLATION ERROR:No aliasing
Decimation factor 4 (8 min)
Conclusion: Real-time systems require much more often calibration time to avoid estimation errors to propagate and increase rapidly
EKF
B ~ 1 mHzTinter-cal max = 1 / 2·B ~ 4 min
If Tinter-cal > 4 min Aliasing interpolation phase error
Real-time Processing Prediction, e.g. with Extended Kalman filter (EKF)
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4.2. Inter-calibration time in off-line systems: SMOS
Data: SMOS (L1 level) Commissioning Phase
Measurement: τ =1.2 s., every 2 minDecimationInterpolation with different methods
No aliasing Optimum inter-calibration time
Best interpolation Methods:• fft• Interp (Sinc)• SplineMax inter-calibration ~7 min(decimation factor ~ 3.5)
All visibilities (fft interpolation)
• At present: 10 min, ~ 1º• But at ~7 min, < 0.3º• And << 7 min, marginal improvement in
Optimum interpolation
B ~ 1.25 mHzTinter-cal max = 1 / 2·B ~ 7 min
If Tinter-cal > 7 min Aliasing interpolation phase error
© UPC IGARSS 2011 Vancouver 24-29 July 2011 9 / 13
5.1. Preliminary results (i): Impulse response
3 sFFT
Point Source : PRN signal (-70 dBm)Moving the Instrument
(no temperature control)
El +/- 10º,
+/- 20º
Az +/- 10º,
+/- 20º
Pol H Az= 0º El= 0º Pol H Az= +10º El= 0º Pol H Az= +20º El= 0º
Pol V Az= 0º El= +10º Pol V Az= 0º El= +20º
PRN SignalRectangular window for
visibility samples
Antenna 1
PRN Source 1
Instrument
© UPC IGARSS 2011 Vancouver 24-29 July 2011 10 / 13
5.2. Preliminary results (ii): Angular resolution
FFT
Point Source : PRN signals (-70 dBm)7 antennas per arm + rectangular window
Sources – PAU-SA distance at 10 m Angular resolution (ξ,η) ~ 5.7º
2 PRN SignalsRectangular window
PRNSource 1
Antenna 1
PRNSource 2
Antenna 2
Instrument
1 m 2 m
3 m 4 m
Antennas separation at:
(Near field) No near-to-far field transformation applied
3 s
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5.3. Preliminary results (iii): GPS satellites
FFT GPS Signal Rectangular window
UTC 12:44:03
K
UTC 12:22:03
KUTC 12:00:03
K
UTC 11:38:03
K
UPC location
GPS orbit 3 s
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5.4. Preliminary results (iv): GPS satellites
K
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6. Summary
PAU-SA Instrument and design drivers briefly described Successful test of use of PRN signals instead of noise for:
Calibration, FWF, and receiver’s frequency response measurement Optimum phase inter-calibration for off-line and real-time instruments.
Real-time processing (PAU-SA): due to a thermal drift, best results using: linear, pchip (piece wise cubic), spline, and fft interpolation techniques (inter-calibration time ~ 4 min)
Off-line processing (SMOS): Best results using: FFT or sinc interp, and reducing inter-calibration time ~ 7 min.
EKF to estimate phase evolution in a real-time system (PAU-SA)
larger error more frequent calibration required (~ 1 min)
Image reconstruction using different PRN sources Impulse response (one source in different positions of FOV)
Angular resolution (two sources with different angular separation) ~ 0.1
Zenith imaging of real GPS satellites: tracking GPS constellation
© UPC IGARSS 2011 Vancouver 24-29 July 2011 14 / 13
Mr. Isaac RamosResponsible for the design and manufacturing of the instrument
Thank you!
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