First results of the PAU Synthetic Aperture Radiometer

© 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


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


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


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


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


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


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)


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


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


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


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


5.4. Preliminary results (iv): GPS satellites

K


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


Mr. Isaac RamosResponsible for the design and manufacturing of the instrument

Thank you!

First results of the PAU Synthetic Aperture Radiometer

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