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  1. 1. <ul><li>First results of the PAU Synthetic Aperture Radiometer </li></ul><ul><li>I. Ramos-Perez, G. Forte. X. Bosch-Lluis, E. Valencia, </li></ul><ul><li>N. Rodriguez-Alvarez, H. Park, M. Vall·llossera, and A. Camps </li></ul><ul><li>E-mail: </li></ul><ul><li>Remote Sensing Lab </li></ul><ul><li>Universitat Politècnica de Catalunya (UPC) – Barcelona, Spain </li></ul><ul><li>and IEEC-CRAE/UPC </li></ul><ul><li>28 th of July of 2011 </li></ul> / 13
  2. 2. Outline <ul><li>Review of PAU-SA instrument </li></ul><ul><li>Potential improvements for future SMOS – like missions </li></ul><ul><li>Use of PRN Signals for: Calibration, FWF Determination, and receiver’s frequency response determination </li></ul><ul><li>Inter-calibration phase determination in post-processing and </li></ul><ul><ul><li>real-time systems </li></ul></ul><ul><li>Some Imaging results: </li></ul><ul><ul><li>Impulse response (near field) </li></ul></ul><ul><ul><li>Angular resolution (near field) </li></ul></ul><ul><ul><li>GPS satellites constellation </li></ul></ul><ul><li>Conclusions </li></ul> / 13
  3. 3. 1. PAU-SA Instrument / 13 PAU-SA in the robotic arm 8 m PAU-RAD PAU-GNSS-R PAU-IR
  4. 4. / 13 2. Potential improvements for future SMOS’s 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 negligible Larger  T Arm size 4 m 1.3 m Altitude Global observation, LEO, orbital altitude ground-based - Antenna type Patch 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 spacing 0.875  at 1400 MHz, (21 cm) 0.816  at 1575.42 MHz, (15.5 cm) Increase the alias-free field of view Receiver type single 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 Quantization 1 bit (Inside the LICEF ) 8 bits IF sub-sampling using a external ADC Digital I/Q demodulation Digital Power measurement Digital LPF I/Q conversion Analog Digital Elimination quadrature error Frequency response shaped by Analog RF filter Digital low- pass filter Mass 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 noise Injection 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
  5. 5. 3.1. Use of PRN Signals for: FWF determination / 13 FWF(Y1Y2) <ul><li>Overcomes limitations of centralized noise injection </li></ul><ul><li>PRN with SR > 5 (flat spectrum such as Noise Source) </li></ul><ul><li>Estimation of FWF at  =0 with 1B/2L </li></ul><ul><ul><li>Amplitude error < 0.25% </li></ul></ul><ul><ul><li>Phase error < 1º </li></ul></ul>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
  6. 6. 3.2. Use of PRN Signals for: Receiver’s frequency response / 13 A S PRN +S R2 S PRN +S R1 Correlation of receivers’ output with local replica of PRN signal injected allows individual frequency responses to be measured (amplitude and phase) Using: PRN sequences
  7. 7. 4.1. Inter-calibration time in real-time systems / 13 Data : PAU-SA instrument Measurement : τ =1 s., every 2 min Off-line Processing  Decimate to simulate lack of data <ul><li>Best interpolation Methods: </li></ul><ul><li>Linear </li></ul><ul><li>Pchip </li></ul><ul><li>Spline </li></ul><ul><li>fft </li></ul>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 mHz T inter-cal max = 1 / 2·B ~ 4 min If T inter-cal > 4 min Aliasing interpolation phase error Real-time Processing  Prediction, e.g. with Extended Kalman filter (EKF)
  8. 8. 4.2. Inter-calibration time in off-line systems: SMOS / 13 Data : SMOS (L1 level) Commissioning Phase Measurement : τ =1.2 s., every 2 min Decimation Interpolation with different methods No aliasing  Optimum inter-calibration time <ul><li>Best interpolation Methods: </li></ul><ul><li>fft </li></ul><ul><li>Interp (Sinc) </li></ul><ul><li>Spline </li></ul><ul><li>Max inter-calibration ~7 min </li></ul><ul><li>(decimation factor ~ 3.5) </li></ul>All visibilities (fft interpolation) <ul><li>At present: 10 min,   ~ 1º </li></ul><ul><li>But at ~7 min ,   < 0.3º </li></ul><ul><li>And << 7 min , marginal </li></ul><ul><li>improvement in   </li></ul>Optimum interpolation B ~ 1.25 mHz T inter-cal max = 1 / 2·B ~ 7 min If T inter-cal > 7 min Aliasing interpolation phase error
  9. 9. 5.1. Preliminary results (i): Impulse response / 13 FFT 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 Signal Rectangular window for visibility samples Antenna 1 PRN Source 1 Instrumen t
  10. 10. 5.2. Preliminary results (ii): Angular resolution / 13 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 Signals Rectangular window PRN Source 1 Antenna 1 PRN Source 2 Antenna 2 Instrumen t Antennas separation at: (Near field) No near-to-far field transformation applied 1 m 2 m 3 m 4 m
  11. 11. 5.3. Preliminary results (iii): GPS satellites / 13 FFT GPS Signal Rectangular window UPC location GPS orbit UTC 12:44:03 K UTC 12:22:03 K UTC 12:00:03 K UTC 11:38:03 K
  12. 12. 5.4. Preliminary results (iv): GPS satellites / 13 K
  13. 13. 6. Summary <ul><li>PAU-SA Instrument and design drivers briefly described </li></ul><ul><li>Successful test of use of PRN signals instead of noise for: </li></ul><ul><li>Calibration, FWF, and receiver’s frequency response measurement </li></ul><ul><li>Optimum phase inter-calibration for off-line and real-time instruments. </li></ul><ul><ul><li>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 ) </li></ul></ul><ul><ul><li>Off-line processing (SMOS): Best results using: FFT or sinc interp, and reducing inter-calibration time ~ 7 min . </li></ul></ul><ul><ul><li>EKF to estimate phase evolution in a real-time system (PAU-SA) </li></ul></ul><ul><ul><li> larger error  more frequent calibration required (~ 1 min) </li></ul></ul><ul><li>Image reconstruction using different PRN sources </li></ul><ul><ul><li>Impulse response (one source in different positions of FOV) </li></ul></ul><ul><ul><li>Angular resolution (two sources with different angular separation)  ~ 0.1 </li></ul></ul><ul><ul><li>Zenith imaging of real GPS satellites: tracking GPS constellation </li></ul></ul> / 13
  14. 14. / 13 Mr. Isaac Ramos Responsible for the design and manufacturing of the instrument Thank you!