SAOCOM Calibration Strategy

Transcription

1 COMISION NACIONAL DE ACTIVIDADES ESPACIALES (The Argentinean National Commission of Space Activities) M. Azcueta, J. Giardini, J. P. Cuesta González, M. Thibeault, T. Zajc November 7-9, 20 October 20 8 CEOS - 2, 2009 SAR Calibration and Validation Workshop Progress In Electromagnetics Fairbanks, Research Alaska, U.S.A. Symposium PIERS 2009 in Moscow, RUSSIA, 8-2 August, 2009 of 27

2 Contents. SAOCOM SAR Instrument Main Characteristics 2. Calibration components 3. External Calibration Model Overview TopSAR modes Calibration sites 4. Internal Calibration Overview Central Electronics Calibration - Scheme Fundamentals Antenna Calibration 5. Summary 2 of 27

3 SAOCOM SAR Instrument MAIN CHARACTERISTICS L-Band SAR Right looking SAR Left looking capability 0m x 3.5m active phased array antenna with 40 TRMs TOPSAR & STRIPMAP acquisition modes Single, dual and quad polarization operative modes More than 2600 beams 3 of 27

4 SAOCOM Calibration Components ANTENNA MODEL SAOCOM CALIBRATION COMPONENTS INTERNAL CALIBRATION ETERNAL CALIBRATION 4 of 27

5 Antenna model Objectives Antenna beams shape Beam to beam and pol to pol gain G S HH S 2HH S 3HH High number of beams S VV S 2VV S 3VV Drivers Workflow Radiometric accuracy optimization On-Orbit calibration effort reduction Pre-Launch extensive characterization Pre-Launch validation (near field/int. Cal pulses) On-Orbit verification & monitoring (rain forest) θ Beam Coefficients Int. Cal Telemetry 5 of 27

6 External Calibration Antenna Model Absolute Calibration Polarimetric Calibration Absolute Calibration constant -talks Imbalances SAR Image External Calibration Antenna Pattern Ionospheric Correction Range and azimuth Ant. pattern Pointing Faraday Internal Calibration Geometric Calibration Geolocation Distorsión Image Quality Impulse response Others 6 of 27

7 L2B Mission System Requirements Summary Antenna Pattern shall be verify from External Calibration with a precisión of 0.2 db. Absolute calibration constant (K) shall be estimated from External Calibration measurements with an uncertainty equal or less than 0.2dB. Crosstalk levels shall be estimated from External Calibration measurements and and corrected so that the residual x-talks is less than -30dB Imbalance (f) shall be estimated with an uncertainty equal or less than 0.dB. Image geolocation error in STRIPMAP mode shall be less than 2 resolution cells. 7 of 27

8 Beams design To limit the calibration effort, all the modes are based on a total set of 8 beams (in range): 9 Quad-Pol 9 Dual- Single Pol TOPSAR mode was chosen to maximize coverage vs geometric and radiometric resolution. 8 of 27

9 TOPSAR Absolute Calibration Rely on the Antenna Model and the fact that the STRIPMAP beams are used to construct the TOPSAR mode Computation of absolute constant using corner reflector for STRIPMAP then conversion to TOPSAR modes Verification using Corners reflector over very low background STRIPMAP TOPSAR W Integration area [pixels] 20 x x 20 Corner RCS σ CR [db] Background σ 0 B [db] σ CR Pixel area A [m²] Confidence error [%] Salt Lakes for CR Single Measurement error [db] Measurements error [db] of 27

10 Calibration Sites for Corner Reflectors # Acquisitions SQP-S 60 SQP-S2 6 SQP-S3 6 SQP-S4 7 SQP-S5 6 SQP-S6 5 SQP-S7 6 SQP-S8 22 SQP-S9 4 Total QP 42 SDP-S 38 SDP-S2 9 SDP-S3 2 SDP-S4 50 SDP-S5 30 SDP-S6 72 SDP-S7 60 SDP-S8 0 SDP-S9 36 Total DP 36 0 of 27

11 Point Targets Some sites are already operative for Airborne and satellites use. Mores sites are planned in the near future SARAT COSMO ALOS of 27

12 L+ Malargue Calibration Site 55 Km² area. Background RCS of -0dB for -band and -5dB for L-band. 500 m height 2% of terrain slope. 2 of 27

13 L+ Malargue Calibration Site Targets 750 m away of any other object 7 L band &2 band 3 of 27

14 Range Antenna Pattern Model Validation Antenna pointing will be verified using a special notch beam (). A subset of beams will be validated: SQP, S4QP, S8QP and S7DP (2). The validity of the model will be assumed for the rest of the beams. TOPSAR images correction will be verified as an end-to-end test (3). 4 of 27

15 Extended Targets Amazon Rain Forest Congo Rain Forest 5 of 27

16 Azimuth antenna pattern and pointing 6 of 27

17 SAOCOM Calibration Components ANTENNA MODEL SAOCOM CALIBRATION COMPONENTS INTERNAL CALIBRATION ETERNAL CALIBRATION 7 of 27

18 SAOCOM Internal Calibration NOISE ACQUISITIONS σ bias estimation CENTRAL ELECTRONICS CAL PULSES INTERNAL CALIBRATION COMPONENTS ANTENNA CAL PULSES Sensor drifts INSTRUMENT TELEMETRY ON GROUND CHARACTERIZATION 8 of 27

19 Sensor Drifts Review of the needs for measuring drifts Sensor designed stable, however there will be drifts ICAL compensates for these drifts => Accuracy Parameter drift measured by ICAL Sensor parameter Parameter drift y Flight path x Sensor External targets z 9 of 27

20 SAOCOM Instrument CDU CR DNH TRM T H H Pol SSG FE R H SSG CAL NW V Pol CE ANTENNA (40 TRMs) 20 of 27

21 CE Calibration - Scheme Fundamentals (/3) T path / pulses A B K T Magnitude drift: K (t = 0 T MD T = KT(t = t0) t ) K K T 0 T To CDU Downconverter From core SSG CR b CR Γ CR b GSS GSS Γ GSS Quadrature modulator K T CAL NW K = T CR,B GSS,B GSS,A CR,A F Input and output signals from cal pulses Paths in pulses A and B and nominal elements T 2 of 27

22 CE Calibration - Scheme Fundamentals (2/3) Scheme Performance Actual: Without considering F T : 0 T K T MD = = K 0 T CR,B 0 GSS,B CR,B 0 GSS,B 0 GSS,A CR,A 0 GSS,A CR,A F F T 0 T EMD = 0 T CR,B 0 GSS,B CR,B 0 GSS,B CR,A 0 0 GSS,A GSS,A CR,A ε MD 0 T EMD 0 T / MD 0 T = + F 0 T / F 0 T Performance depends on the relative change of F T : F 0 T = F T F 0 T 22 of 27

23 CE Calibration - Scheme Fundamentals (3/3) Scattering parameters Partial increments A A 2 A A 2 22 F / F i F v v i i / F Two type of uncertainty sources: A2 / A 2 B2 / B 2 ( + C2 C32 Γ2 / C3) C2 / C2 / ( C22 C2 C32 / C3) Γ A22 + A2 ΓGSS) ( B Γ 2 + A2 ΓCR ) ( A Γ : : GSS CR AS A RESULT: Instabilities of the ICAL NW We obtain the ICAL performance in terms of measurable parameters We understand the influence of each parameter on the total uncertainty We can derive guidelines for ICAL NW design Changes in nominal HW 23 of 27

24 Antenna Calibration Similar concept as for calibration of the CE In-flight measurements of TRMs (PCC) Models of passive devices (AM) TRM Transmission Chain TRM Reception Chain 24 of 27

25 Summary (/2). The SAOCOM calibration Strategy is build upon three features: Antenna Model, External Calibration and Internal Calibration. 2. TOPSAR mode absolute Calibration made use of the Antenna model and the STRIPMAP Calibration with CR s. 3. Many Calibration sites are planned or underway in Argentina for Corner Reflector and use of both Amazon and Congo Forest is envisaged as extended targets 4. Ground receptors are foreseen to be used for both validation of some azimuth beams and pointing. 25 of 27

26 Summary (2/2) 5. The SAOCOM ICAL Strategy was presented focusing on measurement accuracy, together with a proposed method for estimating the ICAL performance 6. The method can be used to drive the ICAL network design, including requirements allocation to its components 7. Potential error sources such as the effect of changes in the reflection coefficients of nominal elements were considered 8. The method is planned to be used for the final version of the ICAL network 26 of 27

27 Thank You 27 of 27

28 Back-Up Slides - CE Transmission Gain CR 3 To CDU From core GSS CR,A Down converter GSS,A Quadrature modulator bcr,a ΓCR CR RF Input Section bgss,a ΓGSS 2 GSS CR RF SW A CT TRRS 3 DC2 2 CAL NW GSS RF Output Section GSS RF SW Figure. Calibration pulse A. CR 3 To CDU From core GSS CR,B Down converter GSS,B Quadrature modulator bcr,b ΓCR CR RF Input Section bgss,b ΓGSS 2 GSS CR RF SW CT TRRS DC2 C 2 3 D 3 2 CAL NW B GSS RF Output Section GSS RF SW Figure 2. Calibration pulse B. CR 3 To CDU From core GSS CR Down converter GSS Quadrature modulator bcr ΓCR CR RF Input Section bgss ΓGSS GSS CR RF SW CT TRRS E G DC2 2 3 F 3 2 CAL NW GSS RF Output Section GSS RF SW 28 of 27

29 Back-Up Slides - All Pulses A B C CE Transmission Chain CE Reception Chain TRM Transmission Chain TRM Reception Chain 29 of 27