- The document discusses the monostatic calibration of the TanDEM-X satellites TerraSAR-X and TanDEM-X. - Key calibration tasks performed on TerraSAR-X in 2009 included geometric calibration, antenna model verification, radiometric calibration, and channel imbalance measurements. - TanDEM-X's monostatic calibration strategy in 2010 involved geometric calibration, antenna pointing determination, antenna model development, and radiometric calibration using test sites. - Preliminary results showed the TanDEM-X transmit pulses were similar to TerraSAR-X, its thermal noise matched ground measurements, and antenna patterns agreed with models and each other to within requirements.

1. Monostatic Calibration of both TanDEM-X Satellites Marco Schwerdt , Jaime Hueso Gonzalez , Markus Bachmann, Dirk Schrank, Clemens Schulz, Björn Döring

2. TSX-1 / TDX-1 In-Orbit Calibration Plan Operational Phase Ant Point Geo Cal GS/SC Checkout TSX-1 Launch (15.06.2007) Radiometric Calibration Ant Model Verification TSX-1 Commissioning Phase 5 Months Summer 2007 TDX-1 Comm. Phase TDX-1 Launch (21.06.2010) 5 Months (Mono + Bi: 3+2) Geo Cal Ant Point • • • • • • Channel Imbalance DRA Campaigns 1 Month Spring 2009 Radiometric Calibration Antenna Model Cross Talk Radiometric Calibration Ant Model Verification Geo Cal TSX-1 Re-Calibration 1 Month Ant Point Summer 2009 ≈ ≈

3. TSX-1 Calibration

4. Geometric Calibration TSX-1 6 corner reflectors per pass 8 beams Near range Far range - Azimuth shift - Instrument delay - Tropospheric effects Time annotation of source packets Range delay Connection between SAR data and geographic position on Earth surface is calibrated 2m ( requirement ) 30 cm (1  ) (2 ns) Pixel localization accuracy (range) No trend since 2 years 3.75 cm (0.25 ns) Residual offset (in-flight  OGC)

5. Pointing Determination in Azimuth TSX-1 Updates Improved ground receiver position Re-adjustment between star trackers Improvements 2007 2009 Measurement accuracy ≤ 7.9 Hz ≤ 2.6 Hz (1  ) per pass < 1.0 mdeg < 0.33 mdeg Mean doppler 16 Hz 5.9 Hz Residual pointing error 2 mdeg 0.74 mdeg Notch patterns with different look angles 4 ground receivers per pass Near range Elevation look angle [degree] Far range Frequency shift due to mispointing [Hz]

6. Antenna Pattern Monitoring TSX-1 ScanSAR-mode: several beams measured during one pass Across an area of 750 x 750 km² Purpose Detect changes in the antenna front end and waveguides 120 km range 60 km azimuth strip_003 strip_004 strip_005 strip_006 Quality parameters *  max µ  min strip_003 strip_004 strip_005 strip_006

7. Antenna Pattern Long Term Monitoring TSX-1 Shape deviation within the main beam Beam-to-beam gain prediction stable, no trend Requirement still fulfilled Δ < ± 0.2dB

8. Radiometric Calibration TSX-1 µ 2009 = -56.53dB + 0.10dB (CR) = -56.43dB µ ≤ ± 0.2dB within scene TerraSAR-X is extremely stable 0.15dB over 2 years µ ≤ ± 0.2dB within full performance range Requirement 0.5 dB (1  ) over 6 months ! CR: corner reflector 6 corner reflectors across the swath 3 beams (low, mid, high inc.) -57,6 -57,4 -57,2 -57 -56,8 -56,6 -56,4 -56,2 -56 -55,8 -55,6 10 15 20 25 30 35 40 45 Look Angle [deg] Abs Cal Factor [dB] strip_002 strip_007 strip_013  = -56.50 dB  = 0.21 dB  = -56.76 dB  = 0.24 dB  = -56.45 dB  = 0.16 dB strip_007 -57,6 -57,4 -57,2 -57 -56,8 -56,6 -56,4 -56,2 -56 -55,8 -55,6 Abs Cal Factor [dB] near mid far  = -56.73 dB  = 0.22 dB  = -56.65 dB  = 0.17 dB  = -56.62 dB  = 0.18 dB  = -56.67 dB  = 0.18 dB Radiometric Stability Abs. Cal Factor 2007 - 56.58 dB 2009 - 56.43 dB ≤ ± 0.2dB Antenna Model

9. Calibration Tasks Performed in 2009 TSX-1 TerraSAR-X in Dual Receive Antenna (DRA) Mode 2 instrument chains on receive (main and redundant) 2 antenna halves Quad-pol mode Along track interferometry DRA Campaigns Geometric calibration Antenna model verification Channel imbalance, phase Channel imbalance, amplitude  radiometric calibration Cross talk Ch. 2 Ch. 1

10. Channel Imbalance: Amplitude TSX-1 -0.18dB antenna gain Correction, V-pol on receive max. offset 0.44dB Channel imbalance 0.26 dB Abs. rad. accuracy during DRA campaigns 0.30 dB (1  ) (45° constellation)

11. One-Way Cross Polar Isolation TSX-1 Ground receivers aligned for V-pol 1-way azimuth pattern measured per pass Cross talk Requirement ≥ 24dB (1-way, StripMap) Receiver for V-pol Strip_013, des, Inc. 43.7° (16-04-2007) H V 1-way cross polar isolation (on transmit) > 34dB

12. TerraSAR-X Calibration Tasks Performed in 2009 C ALIBRATION TerraSAR-X is stable with outstanding performance Slide 12 27 DLR colleagues DRA mode calibration Radiometric stability 0.15 dB (over 2 years) Absolute radiometric accuracy 0.39 dB (StripMap) 0.46 dB (DRA Quad-pol) Channel imbalance 0.26 dB / < 3 deg Cross talk < - 24.9 dB 213 acquisitions 171 over rainforest 42 cal-field (306 targets) Re-calibration 2 years after launch Pointing accuracy < 1 mdeg (azimuth) < 4 mdeg (elevation) Pixel localization accuracy 31 cm (range) 54 cm (azimuth)

13. TDX-1 Calibration

14. TDX-1 Calibration Goals TerraSAR-X calibration performance sets a solid basis ≤ 0.1dB / ≤ 1.0 degree Internal calibration accuracy < 0.7dB Absolute radiometric accuracy ≤ 0.5m (range/azimuth) Pixel localization accuracy ≤ 0.2 dB (requirement) Antenna model accuracy < 2 mdeg (azimuth) < 10 mdeg (elevation) Pointing accuracy TDX-1 Calibration Goals SAR Quality Parameter

15. TDX-1 Monostatic Calibration Strategy 2.5 months (summer 2010) Geometric calibration Antenna pointing Antenna model Radiometric calibration StripMap and ScanSAR Cal test sites * Rainforest: distributed field * South Germany: 30 calibration sites from which 17 are permanently installed corner reflectors TanDEM-X calibration team 32 DLR colleagues Around 60 calibration campaigns with reference point targets: transponders and corners More than 1000 datatakes will be analyzed

16. Calibration Field in South Germany near by Oberpfaffenhofen Munich D01 x D02 x D03 x D04 x D05 x D06 x D07 x D24-D30 x x x x x x x D08 x D09 x D10 x D12 x D14 x D17 x D18 x D19 x D20 x D22 x D11 x D13 x D15 x D16 x D21 x D23 x 40km 120km S007 S007

17. First Results: Chirp Comparison of TDX-1 – TSX-1 Receive pulses, BW = 150MHz, UP-chirp, pulse length = 32µs Similar spectrograms image frequencies chirp TSX-1 TDX-1 important for bistatic operation

18. First results TDX-1: TRM Characterization – PN Gating blue: measured in flight cold red: measured in flight hot black: on ground characterization Receive Phase [degrees] Amplitude [dB] Transmit Phase [degrees] Amplitude [dB] Warm instrument stability

19. First Results TDX-1: Antenna Pattern over Rainforest Within requirements strip_003 strip_004 strip_005 strip_006 strip_003 strip_004 strip_005 strip_006

20. First Results TDX-1: Antenna Pattern by Ground Receivers Ground Receiver Position Vector Measurements confirm simulated reference pattern Within requirements Transmit pattern only Relative accuracy < ± 0.1dB

21. First Sequential Ground Receiver Acquisition Direct measurement of the satellite separation in along track  Pursuit monostatic phase 1 st absolute comparative measurement of transmitted power  <0.5dB difference TDX-1 – TSX-1 3s azimuth separation ≈ 20 km TSX-1 TDX-1 RX

22. Questions? THE END TSX-1 DLR logo experiment : Oberpfaffenhofen, Bayern, Germany (19 th June 2008)