TerraSAR-X SAR Data Processing

Transkript

1 TerraSAR-X SAR Data Processing H. Breit, T. Fritz, U. Balss, A. Niedermeier, M. Lachaise, B. Schättler CEOS SAR Calibration and Validation Workshop 2008

2 Content TerraSAR Multi-Mode SAR Processor (TMSP) Functional Overview Calibration Pulse Processing and Replica Generation Spectral Weighting Product Location Accuracy and Radiometric Accuracy Noise Correction H. Breit et al., slide 2 Folie 2

3 TMSP Functional Overview TMSP Screening Data Assessment, CAL, QLs Datatake + Aux. Products L0 Product DEM TMSP L1b Processing Proc. Parameter Gen. Multi-Mode SAR Correlator Detection and Multilooking (optional ground projection) Geocoding Annotation SSC MGD MSD GEC intermediate components Product Formatter EEC L1b Product SSC or MGD or GEC or EEC H. Breit et al., slide 3 Folie 3

4 Stripmap TerraSAR-X Imaging Modes and Synthetic Apertures f Doppler target t bandwidth length of focused scene Sliding Spotlight f Doppler target bandwidth t ScanSAR f Doppler length of focused scene target bandwidth t Burst #1 Burst #2 length of focused scene H. Breit et al., slide 4 Folie 4

5 Radiometric Calibration Internal calibration (calibration pulses track gain and phase drifts of the instrument during a data take). Calpulse evaluation Correction of calibration pulses for temperature and Rx-duty cycle dependency in the TMSP. Replica generation Processor normalization Projection of the elevation antenna pattern based on attitude data using DEM data Azimuth antenna pattern correction based on Doppler centroid (geometry and signal) estimates. External calibration (corner reflectors, transponders, antenna pattern models) provides antenna patterns and calibration constant. H. Breit et al., slide 5 Folie 5

6 Instrument gain drift covered by interleaved cal. pulses 0.2 db temperature correction instrument gain drift observed by interleaved cal.pulses Rx-duty cycle correction -0.9 db 30 s H. Breit et al., slide 6 Folie 6

7 Digital Replica Focusing Spectrogram of a digital 100 MHz down-chirp replica reconstructed from the instrument s internal calibration loop measurements. Besides the nominal chirp additional chirp frequency rates are present H. Breit et al., slide 7 Folie 7

8 Stripmap SSC, , θ 26, Yokohama, Japan H. Breit et al., slide 8 Folie 8

9 Range reference function: 5th order polynomial chirp H. Breit et al., slide 9 Folie 9

10 Range reference function: digital replica chirp H. Breit et al., slide 10 Folie 10

11 A short and rare (< 1 ) visit in the trap of blind deconvolution H. Breit et al., slide 11 Folie 11

12 Range Compression with Spectral Thresholding ADC offset corrections applied during replica generation may cause the DC-part of the replica to be close to zero. In case of a DC-part in the SAR signal not as close to zero as in the replica (due to noise and/or differing ADC offsets) this signal component is improperly high amplified during range deconvolution: RC(f) = U(f) / Replica(f) μ DC-part of replica DC-part after thresholding Spectral thresholding of the filter avoids over-amplification of the frequency bins close to zero Part of the TMSP since V4.2, 0.25 μ April 08 H. Breit et al., slide 12 Folie 12

13 High Resolution Spotlight Image of Anak Krakatau Improperly amplified DC-part of SAR image => range stripes H. Breit et al., slide 13 Folie 13

14 High Resolution Spotlight Image of Anak Krakatau Spectral thresholding eliminates range stripes H. Breit et al., slide 14 Folie 14

15 Range & Azimuth Spectral Weighting - from a theoretical point of view - ρ = 1.00 ρ = 1.18 IRF(α = 0.75) IRF(α = 0.60) 10 db α ρ PSLR ISLR db -16 db db db H. Breit et al., slide 15 Folie 15

16 Spectral weighting improves Signal to Azimuth Ambiguity Ratio H. Breit et al., slide 16 Folie 16

17 Spectral weighting improves Signal to Azimuth Ambiguity Ratio α = 0.75 α = 0.60 visible azimuth ambiguities in a Spotlight image acquired out of the fullperformance range H. Breit et al., slide 17 Folie 17

18 MGD-SE, 3m resolution, α = 0.75, BW azimuth: 2500 Hz H. Breit et al., slide 18 Folie 18

19 MGD-SE, 3m resolution, α = 0.60, BW azimuth: 2765 Hz H. Breit et al., slide 19 Folie 19

20 High Resolution Spotlight SSC, 300 MHz, θ Ceuta, Spain H. Breit et al., slide 20 Folie 20 Institut für Methodik der Fernerkundung bzw. Deutschesder Fernerkundungsdatenzentrum Institut für Methodik Fernerkundung

21 α = 0.75 High Resolution Spotlight SSC, 300 MHz, θ Ceuta, Spain H. Breit et al., slide 21 Folie 21 Institut für Methodik der Fernerkundung bzw. Deutschesder Fernerkundungsdatenzentrum Institut für Methodik Fernerkundung

22 α = 0.60 High Resolution Spotlight SSC, 300 MHz, θ Ceuta, Spain H. Breit et al., slide 22 Folie 22 Institut für Methodik der Fernerkundung bzw. Deutschesder Fernerkundungsdatenzentrum Institut für Methodik Fernerkundung

23 Range & Azimuth Spectral Weighting - in real TerraSAR-X SSC PSLR SM / SL life (S/D) - left db Az Rg nr. SSC PSLR SM / SL (S/D) - right db Az Rg nr. H. Breit et al., slide 23 Folie 23

24 db Range & Azimuth Spectral Weighting SSC PSLR SM / SL (S/D) - left - in real TerraSAR-X life Az SSC ISLR SM / SL (S/D) Rg Az Rg nr. db db SSC PSLR SM / SL (S/D) - right Az -21 Rg -23 nr nr. H. Breit et al., slide 24 Folie 24

25 HS 300 MHz D28 Corner Reflector Analysis D28 Tiefenbrunn H. Breit et al., slide 25 Folie 25

26 Corner Reflector Analysis in HS 300 MHz Single Pol SSC (HH) measured resolution 1.1 m (az) 0.6 m (sl rg) specified resolution 1.1 m (az) 0.6 m (sl rg) H. Breit et al., slide 26 Folie 26

27 Geometric Corrections internal delay Orbit state vectors (COG) are shifted to the geometric SAR antenna center using the current instrument attitude information during processing (approx. 80cm in range). These are the annotated state vectors. c<c vac i h TS-X products contain annotation of signal propagation delay: operational tropospheric delay correction by processor TMSP: h ZPD Z H ΔRtropo( h) = e cos( i) ZPD = 2.3m; H = 6000m h = avr. DEM height of scene i = mid scene incidence angle ionospheric delay not significant for X-band: ΔR θ iono near range (18 deg.) far range (41 deg.) K TEC f 2 cosi TEC [TECU] h = 0 m 2.4 m 3.1 m h = 2500 m 1.6 m 2.0 m Delta R Z [m] H. Breit et al., slide 27 Folie 27

28 Pixel Localization Accuracy achieved orbit accuracy is well within spec. (science orbit error << 20cm). Currently (low solar activity) close to 3cm. Rapid orbit accuracy is very close to science. tropospheric delay correction refined and adjusted in collaboration with calibration team. L1b products are localized in sub-pixel range. Measured absolute pixel localization accuracy OP-CRs (rg/az): 30 cm / 53 cm (1sig) independently verified by PASCO Tokyo CR measurements in CP (39 cm / 58cm) specified absolute location error < 1 m (sigma, SSCs, science orbit) including orbit errors (along track), propagation with different heights Example: ascending / descending Oberpfaffenhofen corner targets multi-temporal EEC overlay (incl. DEM error) H. Breit et al., slide 28 Folie 28

29 Rg Az H. Breit et al., slide 29 Folie 29

30 Product Verification / Validation with respect to Radiometry Rainforest image analysis to verify and validate correctness of elevation antenna patterns correctness of elevation antenna pattern projection (geolocation and projection using a 10 DEM) Compensation of chirp energy variations and instrument gain drifts processor normalization for all imaging-modes Mosaics of standard L1b EEC products originating from different imaging modes and incidence angles have been transformed from β 0 to γ 0 using the annotated incidence angle mask. H. Breit et al., slide 30 Folie 30

31 Rg Az Radiometry Multi-Mode Mosaic β 0 i = Products T. Fritz

32 γ 0 = β 0 * tan( i x,y ) ScanSAR + Stripmap + Spotlight Mosaic radiometrically corrected with local incidence angle i Products T. Fritz

33 Noise Correction The (receiver) noise level is measured for each data take by Rx-only calibration pulse sequences prior and after image acquisition From that, a noise annotation is derived taking into account the spacevariant processor noise-gain (e.g. elevation beam correction and ScanSAR azimuth pattern correction). This noise annotation is part of the L1b-product XML-annotation-file. Due to the fact that the application of the space-variant noise annotation to the image data might be a burden to the user, all detected radiometrically enhanced products (MGD-RE, GEC-RE, EEC-RE) will be corrected for noise with the next processor release (December 1 st ). The correspending flag in the L1b-product XML-annotation-file will be switched accordingly. H. Breit et al., slide 33 Folie 33

34 ScanSAR Image without Noise Correction noise pattern affects low backscatter regions in ScanSAR datatakes SNR at Sea Surface: approx. 0 db at burst center approx. -3 db at edges of burst (!) U. Balss 2008 H. Breit et al., slide 34 Folie 34

35 Noise Reduction by Subtraction of RMS of Noise Amplitude There remains still some residual noise! U. Balss 2008 H. Breit et al., slide 35 Folie 35

36 Analysis of Residual Noise probability density RMS of noise amplitude below RMS, noise is over-compensated above RMS, residual noise remains noise amplitude For high SNR: In mean, the influence of both shown effects on signal power compensate each other. For low SNR: Over-compensation of noise is limited because signal amplitude cannot be lowered below zero. Thus, both effects are no longer balanced and mean signal power is still affected by residual noise. U. Balss 2008 H. Breit et al., slide 36 Folie 36

37 SNR Adaptive Scaling Factor scaling factor significant deviation from 1 if SNR is low approx. 1 If SNR is high SNR [db] U. Balss 2008 H. Breit et al., slide 37 Folie 37

38 Without Noise Compensation H. Breit et al., slide 38 Folie 38

39 Usage of RMS of Noise Power as Clipping Level H. Breit et al., slide 39 Folie 39

40 Usage of SNR Adaptive Clipping Level H. Breit et al., slide 40 Folie 40

41 Without Noise Compensation H. Breit et al., slide 41 Folie 41

42 Usage of RMS of Noise Power as Clipping Level H. Breit et al., slide 42 Folie 42

43 Usage of SNR Adaptive Clipping Level H. Breit et al., slide 43 Folie 43

44 Noise Compensation For All RE Products: HH/HV SM Dual Pol Quicklook without with H. Breit et al., slide 44 Folie 44

45 Mosaic of 41 Spotlight EEC RE Standard Products Tool for automatic mosaicking and calibration by T. Fritz / M. Lachaise (DLR IMF-SV) Folie 45 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute