TerraSAR-X Products Tips and Tricks

Transcription

1 TerraSAR-X Products Tips and Tricks Thomas Fritz Helko Breit Michael Eineder (L1b Annotation, Geometry, Radiometry) (Processing, Spectral Properties) (InSAR-Processing incl. Spotlight) DLR Remote Sensing Technology Institute (IMF) TerraSAR-X Science Meeting

2 1st Part: Comments on Questions Asked and Issues Raised During the Workshop (T. Fritz) This material is distributed for educational & test purposes only. The information is provided "as is". No warranty of any kind given. For TerraSAR-X product and format specifications refer to the current versions of the relevant documentation distributed by the commercial and science service segments. Folie 2 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

3 detected MGD Az Rg TS-X Level 1b Product Types DEM geocoded EEC one unified processing system TMSP & one product annot. format Multi-Temporal HS300 Train of the track (Tehachapi-Loop) ellipsoid geocoded GEC East North Interferogram Tokyo HS 300MHz complex SSC Multi-Temporal HS300 MHz Mosaic & Asc./Desc. Multi-Temp. Flood near St. Louis (June 2008) IMF-SV Products T. Fritz

4 TerraSAR-X L1b Product Annotation Basics all precise annotation refers to the time domain t, tau either focussed zero Doppler time (coordinates, noise polynomials, ) or raw data time (Doppler measurements, instrument setting changes, ) varying parameters are provided as polynomials in range time tau, updated at discrete azimuth times t. the geo grid (GEOREF.xml) translates times in coordinates. Pixel position related parameters are for informative purpose only. the basis for the annotation is the (intermediate) SSC, subsequently supplemented by productspecific annotation (MGD, GEC/EEC) and binary components (mapping grid, geocoded incidence angle mask GIM) derivation of a parameter value from the annotation for a specific (geocoded) image position requires to use the MAPPING_GRID.bin to obtain the interpolated t,tau pair for this position. Folie 4 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

5 Geometry & Projections Folie 5 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

6 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] Folie 6 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

7 Azimuth Position & Time Shift the azimuth time for a range line is the one on ground: t_rx - tau/2 ( tau= t_rx t_tx ) annotated az. time t & ref. position the position is the GEOMETRIC τ/2 position perpendicular to the orbit at this time ( zero Doppler time ; nothing to do with measured or applied Doppler centroid) recommended orbit interpolation technique annotated in product: <recprocessingtechnique>chebyshev <recpoldegree>7 result of geometric calibration measurements: average azimuth time offset Δt shift = msec measured 90 v receive time thus: t corr = t 0 - Δt shift Δaz 7065 m/sec * (-0.18 msec) = m azimuth time shift annotation in GEOREF.xml: <azimuthshift modelname="external azimuth time shift" modelversion="1.0" source="timing"> <coefficient exponent="0"> e-04</coefficient> </azimuthshift> TSX Products Tips and Tricks - T. Fritz

8 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 corner ID azimuth offset ds [m] DT 0844 DT 1556 slant range dr [m] DT 0844 DT 1556 multi-temporal EEC overlay D24 D D D D D mean sigma Folie 8 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

9 Geometric Accuracy of Products all these corrections are performend inside the processor TMSP and used for geolocation, coordinate annotation and geocoding! => no need to account for them if using geocoded products. but if you want to obtain precise geolocation from the (instrument) timing information in complex products, the annotated corrections have to be applied (as the processor does for geolocation) TSX Products Tips and Tricks - T. Fritz

10 Different Product Types and Corrections I: SSCs SSCs: slant range (fast time) / azimuth (slow) time geometry all annotated times are measured instrument times (internal delay corrected and referencing to the time between Tx and Rx). all annotated coordinates (scene & georef.xml) are corrected for the propagation & timing effects annotated orbit state vectors are shifted to the SAR antenna center the azimuth position is corrected by a constant externally provided timing offset from the calibration campaign (~ -1.3m) the applied propagation delay times/shifts are provided in the georef.xml. the scene corner coordinates refer to the valid focussed scene and pixels in the CoSAR file. Lat/lon scene corner coordinates refer to the (coarse) 10 DEM heights which are also used for the georef.xml coordinate grid. The geo-location/ranging is accurate in the cm-range if fast and slow time position derived from measured image pixel positions are corrected for the annotated delays and use the annotated orbit state vector positions in WGS84-G1150 (for Science orbit accuracy and nearly all times also for Rapid orbits). Folie 10 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

11 Range Time Annotation Range times give the two-way radar pulse traveling time. Range times are corrected by known instrument internal delays (as annotated in the IOCS auxiliary product). Range times are not corrected for atmospheric influences. Range times refer to zero Doppler location. Slant Range distance: R 0 = c 0 2 τ <rangetime> <firstpixel> e-03</firstpixel> <lastpixel> e-03</lastpixel> </rangetime> thus: slant range to first pixel slant range to last pixel km km TSX Products Tips and Tricks - T. Fritz

12 Atmospheric Slant Range Delay additional slant range time offset Δτ atm = E-10 sec E-08 sec = E-08 sec thus: additional slant range offset: ΔR atm = m total slant range R total = R + ΔR c = ( τ 0 + Δτ 2 0 atm atm atmospheric signal delay influences have to be taken into account for high accuracy geometric considerations ) TSX Products Tips and Tricks - T. Fritz

13 Geographical Location Information Additional slant range delay and azimuth time shift are taken into account when calculating and annotating the geographical coordinates Annotated WGS 84 coordinates: ( λ, φ, h) WGS = F( t0 Δt shift, τ 0 + Δτ 84 atm t 0 = annotated UTC Δt shift = azimuth time shift τ 0 = annotated range time Δτ atm = atmospheric slant range delay ) TSX Products Tips and Tricks - T. Fritz

14 Georeference Grid Annotated in each grid point in GEOREF.xml: t tau lat lon row col inc elev azimuth time offset to azimuth reference time in seconds slant range time offset to range reference time in seconds latitude in degrees longitude in degrees SSC row number SSC column number incidence angle in degrees (also for σ0 correction) elevation angle in degrees elev local surface normal inc 90º TSX Products Tips and Tricks - T. Fritz

15 Interpolaton Between Grid Points Reference grid allows linear interpolation between grid points to derive georeference information at requested slant range and azimuth time <recinterpoltechnique> <azimuth>linear </azimuth> <range>linear</range> </recinterpoltechnique> <recinterpolpoldegree> <azimuth>1</azimuth> <range>1</range> </recinterpolpoldegree> Illustration Example: Incidence angle range azimuth iaz = 5 row = 2293 iaz = 6 row = 2867 irg = 8 col = E E+01 irg = 9 col = E E+01 Linear interpolation between the annotated values leads to an incidence angle of about at range pixel TSX Products Tips and Tricks - T. Fritz

16 L1b Polynomials value τ Range polynomial 1 Value Range polynomial 2 Value 1 Value 2 polynomial validity range τ τ0 reference time for (τ τ0) polynomial t 1 t t 2 t TSX Products Tips and Tricks - T. Fritz

17 Different Product Types and Corrections II: MGDs MGDs: NOT GEOCODED(!) ground range on average height above ellipsoid / azimuth geometry (image data coarsely oriented in North/East) with coarse Lat./Lon. coordinates. all annotated coordinates (scene & georef.xml) are consistently taken from the same grid as the SSC product coordinates and refer to the same coarse DEM, MGD pixel positions are different from SSCs due to the applied projection and multi-looking. the projection polynomial which translates fast times (using the reference fast time) to ground range is given for the average scene height above the ellipsoid. Azimuth spacing is constant in time thus varying on ground (depending on local zero-doppler-velocity). This polynomial and the azimuth annotation allow to (re-)project fast times and slow times to positions with cm-accuracy. Since the image data linear azimuth and range orientation orthogonality is preserved, the GeoTIFF projection is only of limited accuracy. The scene corner geo-location results are used to derive the GeoTIFF transformation matrix but higher order terms representing the Earths curvature are not included (the geocoded GECs and EECs are provided for this purpose). Folie 17 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

18 MGD Orientation & GeoTIFF Representation Problem Right NORTH Left Folie 18 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

19 Geolocation Discrepancies when Mapping the MGD Az. / Rg. Geometry to the GeoTIFF Raster Az-Rg-Raster-to-curved-surface projection problem of the GeoTIFF file is depending purely on the image-raster-extent. + range offset from average height but with the Mapping Grid (or the anntotated projection polynomial) and the Geo Grid, the localisation of a measured image position by reprojection is accurate Folie 19 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

20 Projection of SSC to MGD and vice versa The product type MGD has nice properties like very precise interpolation and multilooking free of aliasing due to adequate oversampling of complex data prior to detection. Quadratic on-ground pixel spacing Therefore MGD products are very suitable for classification and feature extraction. But, the geometric projection is not very useful. Therefore the SSC-> MGD projection functions are kept very simple in order to facilitate easy (real or virtual) back projection of the data into the original slant range geometry. Folie 20 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

21 Options for Geo-Referencing of MGD data If the interest is to know the precise point-wise geo-location of certain pixels, features or classification results there are two options: Use the provided annotation files MAPPING_GRID.bin and GEOREF.xml or Use the annotated higher-order slant-range-to-ground-range (SLT2GR) polynomial for range projection and the annotated zero-doppler velocity for first-order azimuth projection. If the interest is to obtain a complete geo-referenced image in a projection of choice the two separated MGD<->SSC projection functions can be easily incoorpated into any (high-precision) user-defined projection, relating map-coordinates to azimuth time t, and range delay τ using the precise orbital state vectors and DEM data. Folie 21 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

22 Accuracy of MGD to SSC re-projection using polynom inversion 0.3 μm 0.0 μm -0.6 μm Folie 22 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

23 Different Product Types and Corrections III: EEC/GEC EECs/GECs: image data mapped onto UTM (polar regions: UPS) coordinates using a precise DEM (or average DEM height (GEC)) annotated coordinates in scene & georef.xml annotation section are consistently taken from the same grid as the SSC product coordinates and refer to the same coarse DEM. The frame coordinates of the GeoTIFF file and the processed UTM scene corner coordinates are provided in the relevant XML annotation section. All propagation delays are taken into account during geocoding. GeoTIFF coordinates are precise with errors resulting only from the accuracy of the DEM used for geocoding (i.e. SRTM) plus localization error (<1m). Projection onto UTM-Zone allows cm accuracy for GeoTIFF image positions if the DEM would be as accurate. Overlays of EECs from arbitrary viewing geometries match on sub-pixel level for areas with sufficient DEM accuracy. The GEC is projected onto the average height above the ellipsoid provided since it more or less preserves the radar geometry in range while avoiding the projection accuracy limitations of MGDs Folie 23 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

24 HS 150 s078 HH HS 150 s113 VV HS 300 s043 HH i =36 58 Rg Az Δi Δx Δh = real height vs. DEM used for geocoding (projection error not in SSCs) Products T. Fritz

25 Handling of GECs with different average heights Using average height yield a more precise geolocation in MGDs & GECs but complicate direct comparison, mosaicking of different (but same orbital track) GEC products due to the different projection in range and resulting offsets in Northing and Easting (depending on the scene center heading angle). Even repeated acquisitions may deviate in Haver due to slightly different coverages. Coarse height-offset to ground-range-offset to Northing / Easting offset correction pseudo code: deltarange = deltaheight / tan( scenecentercoord.incidenceangle ); if (Left-Looking) deltarange = -deltarange; if (Descending) {OffsetE = - deltarange * cos(headingangle-180); OffsetN = deltarange * sin(headingangle-180);} else {OffsetE = deltarange * cos(360-headingangle); OffsetN = deltarange * sin(360-headingangle);} Folie 25 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

26 Geometric Accuracy of L1b Products Sydney HS 300 MHz (HH) blind multi-temporal overlay from L1b product info only (descending right: DR) Rg Az IMF-SV Products T. Fritz

27 Rg Az Sydney HS 300 MHz i=21 GEC SE (on same scene height) relative product geolocation error << 1m calibrated σ 0 IMF-SV Products T. Fritz

28 FOGO Mosaick of three Stripmap GEC RE Products with height correction Acquisitions in 3 different beams from same orbital track. Radar geometry is preserved. Global height shifts are coarsely compensated. Radiometric calibration is only possible to β0. T. Fritz / M. Lachaise (DLR IMF-SV) Folie 28 Institut für Methodik der Fernerkundung Deutsches Fernerkundungsdatenzentrum Remote bzw. Sensing Technology Institute

29 Radiometry Folie 29 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

30 Radiometric Calibration and Corrections (EECs) T. Fritz / M. Lachaise (DLR IMF-SV) Folie 30 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

31 Tenerife Mosaic of 41 Spotlight EEC RE Standard Products Obtained from a Coverage Test Order Acquisition Dates: Imaging Mode: SL (10 km x 10 Polarisation: Single (HH) Pass & Look Dir.: Ascending, Right Beams: spot_034 spot_092 Resolution of mosaicked image: 4 m. Calibration to σ 0 using local geocoded incidence angle mask. Tool for automatic mosaicking and calibration by T. Fritz / M. Lachaise (DLR IMF-SV) Folie 31 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

32 Calibration Constant / Factor & Noise (current & stable) calibration constant is dB but each image is individually scaled for optimized use of 16 bit data representation (<Digital Numbers> ~ 150) => use EOWEB proc. gain attenuation for CRs bright CRs Image data represented in (SSCs) but image contains additive noise, expressed as image data noise power in annotated polynomials use same calfactor k s for noise power to obtain NEBN then subtract from Image data to obtain corrected data (caveat: this is a statistical superposition of signal & noise PDFs). corrected incidence angle can be derived from GEOREF.xml (or the GIM for EECs) Folie 32 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

33 Radiometry: Elevation Pattern Correction G(α) Antenna Pattern: gain projected with DEM in time domain for each channel beam gain pattern coarse DEM (10 ) τ t τ t applied gain pattern IMF-SV IGARSS 2008 TS-X Products T. Fritz

34 Radiometric Accuracy of L1b Products Example: Stripmap mosaic of 3 rainforest acquisitions with different incidence angles i = product specific calibration / scaling factor applied radar brightness: beta nought β 0 = k * DN 2 IMF-SV Products T. Fritz

35 σ 0 = β 0 * sin( i x,y ) illumination correction: Sigma nought from local incidence angle i using the EEC product component GIM delivered in same raster as sep. GeoTIFF m DEM geocoded incidence angle mask GIM: i (n,e) from acq. geometry IMF-SV Products T. Fritz

36 γ 0 = β 0 * tan( i x,y ) Radiometrically corrected Gamma nought suitable for volume scatterers with local incidence angle i from EEC product component GIM (geocoded incidence angle mask) IMF-SV Products T. Fritz

37 γ0 Beam: strip 11 (i ~ 40 deg) Beam: strip 03 (i ~ 20 deg) IMF-SV Products T. Fritz

38 CANARY ISLANDS - Isla de la Palma Mosaick of three Ascending & Descending Stripmap EEC RE Products Using Shadow and Layover Mask from the GIM Geocoded shadow and layover maps are used to mask out these regions and to fill the gaps with the data from other viewing geometries if possible. Radiometric calibration to σ 0 is based on local geocoded incidence angle mask. T. Fritz / M. Lachaise (DLR IMF-SV) Folie 38 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

39 Precise Radiometric Correction: Noise Compensation DLR IMF-SV TSX Products T. Fritz

40 TerraSAR-X Product Quality Improvement noise pattern in low backscatter areas typical for ScanSAR results from azimuth and elevation antenna pattern correction for the individual bursts signal is perfectly calibrated but additional noise power is inhomogeneously distributed complex superposition of statistical signal and noise distributions complicates some applications (e.g. ship detection) ScanSAR Sydney, Australia ( ) Folie 40 Institut für Methodik der Fernerkundung Deutsches Fernerkundungsdatenzentrum Remote bzw. Sensing Technology Institute

41 TerraSAR-X Product Quality Improvement blue (enhanced): noise pattern compensation can be performed - from L1b annotation or - in processor (statistical correction see presentation H. CEOS) latter will be activated on December 1st for all TSX RE products Folie 41 Institut für Methodik der Fernerkundung Deutsches Fernerkundungsdatenzentrum Remote bzw. Sensing Technology Institute

42 TerraSAR-X Product Quality Improvement noise corrected product processingflags: noisecorrectedflag = true Folie 42 Institut für Methodik der Fernerkundung Deutsches Fernerkundungsdatenzentrum Remote bzw. Sensing Technology Institute

43 TS-X ScanSAR Product (MGD) DLR IMF-SV TSX Products T. Fritz

44 Without Noise Compensation DLR IMF-SV TSX Products T. Fritz

45 L1b: Annotated Noise Profiles Projected into Image Domain + (x,y( x,y) + (x,y( x,y) 1 0 Map. Grid t,τ (x,y) L1b annot. (t,τ) relative weighting, overlaps from annotation in ScanSAR product DLR IMF-SV TSX Products T. Fritz

46 Noise Compensation from L1b Annotation DLR IMF-SV TSX Products T. Fritz

47 Noise Compensation with Scaled Noise Power (TMSP internal) residual variations from scalloping (residual Doppler or beam pattern errors) DLR IMF-SV TSX Products T. Fritz

48 Noise Compensation For All RE Products: Dual Polarization Quicklook without with (internal) Folie 48 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

49 Gain-Adaption of Quicklooks quicklooks of long SM / SC data takes are generated in individual scenes corresponding to the standard L1b length 8bit dynamic range is adapted to the scene content (0 meanx2.7) and thus close to the noise level for low backscatter areas the individual QLs are then combined to an assembled QL referencing to one mean put correspondingly different cut levels The blocks visible in long DTs of high contrast areas are NOT artifacts in the data or instrument gain setting switches Folie 49 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum

50 Quicklook Scaling: 16bit Image data to 8bit conversion x IMF-SV / Project internal Products T. Fritz

51 radar brightness: beta nought β 0 = k * DN 2 IMF-SV / Project internal Products T. Fritz

52 EOWEB QUICKLOOK Scaling: low BCS are darker (& have a low clipping), bright areas may be clipped IMF-SV / Project internal Products T. Fritz

53 Stripmap, dual polarization East Greenland, glaciers, Polarisation: HH/HV Incidence Angle: deg (beam: stripnear_005 R) HH,HV,HH-HV HV HH Range dir. Flight direction (Desc) 15 km Folie 53 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum

54 Example: Koshi River Nepal/ India Aug Spotlight Embankment breach Folie 54 Institut für Methodik der Fernerkundung Deutsches Fernerkundungsdatenzentrum Remote bzw. Sensing Technology Institute

55 the surf in (high resolution) spotlight data takes (e.g. HS 300) defocussing & decorrelation of small and fast waves / water surfaces long integration (> 1s SL) & λ/8 only 4mm high resolution <-> small fast moving structures Products T. Fritz

56 TerraSAR-X Doppler Centroid Estimation Statistics Doppler centroid distribution of all data takes (July 2008) Distribution of average SAR signal Doppler centroid of each data take confirms Total Zero Doppler Steering prediction. (H. Fiedler, T. Fritz, R. Kahle) Folie 56 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

57 v Doppler Estimation Approach - Geometry b Ψ Velocity vector derived from orbit product, beam vectors determined from IOCS Aux and attitude product. DEM height used for translation of geometric scene layout to grid of range-azimuth times => f DC (t,τ) t f=0 τ H t raw Folie 57 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

58 TerraSAR-X Multi-Mode SAR Processor (TMSP) Doppler Estimation Implementation I - Geometry Orbit & Attitude Products Acquired data take Instr. settings (timing, ) TMSP internal geolocation grid: (lat, lon, i, h, elev. t, τ Geometric Doppler estimates DEM (10 ) Instrument characteristics (antenna pattern, beam pointing, calibration data, ) Radiometric correction Processing parameter calculation Folie 58 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

59 TerraSAR-X Multi-Mode SAR Processor (TMSP) Doppler Estimation Implementation II Data Fusion Doppler centroid grid of SAR signal baseband signal Doppler centroid (rainforest) azimuth time t τ range time f dc [Hz] t / [s] selection which fit or which combination is used for proc. combined Doppler in L1b A Doppler centroid value of ~80 Hz corresponds to a squint angle of 0.01 deg => SAR signal based estimates verify the AOCS measurements geometric Doppler centroid Folie 59 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

60 f dc / [Hz] TerraSAR-X Challenges: Spotlight Mode Doppler Ambiguity Unwrapping PRF ambiguity bands from geometry azimuth beam sweep (squint +/ deg) t / [s] Doppler centroid varies by ~12000Hz / 3s. PRF ambiguity band derived from geometry. Supporting unwrapping of SAR signal Doppler centroid estimates. Folie 60 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute

61 Doppler Centroid Estimation Details (Dual Pol) The signal based "baseband" Doppler centroids of each channel are determined individually for numerous patches in rangeazimuth and than fused with the "geometric" Doppler centroids which are estimated from orbit, attitude, characterized antenna pattern pointing vectors and their projection on DEMs of the scene. Fusion means that first of all the ambiguity unwrapped and secondly outliers are eliminated. That results in the annotated "combined" Doppler estimate (in most cases - see below). Note that in all three cases not the measurements are annotated but the azimuth-range polynomial surface fit results. The "combined" Doppler is always the Doppler which is the input for the processor - which (depending on the mode) in itself applies some averaging for block processing. In Rainforest scenes (see example above), the geometric estimates and the baseband estimates agree very well besides the mentioned beam pointing offsets. The residual variations visible in both plots are the result of the attitude steering loops. However when several weighted quality indicators of the signal estimates fall below some thresholds, the baseband Doppler estimates may even be discarded completely and the "combined" Doppler is replaced by a copy of the very precise geometric estimates. In case of co-/cross-polar data, the cross-polar Doppler might also be replaced by the co-polar data if the quality indicators are sufficient. A rather low signal Doppler estimation quality is especially found for high contrast scenes. Low backscatter values with high errors in Doppler estimates worsen the "baseband" statistics further. Additional differences between two polarisation channels in the signal Doppler estimates will occur e.g. from measurement accuracy limitations and the signal properties (i.e. low backscatter in cross-polar channels, dominant scatterers, bright sea surfaces in VV,...). Especially wind troubled water bodies are rather strong in VV - resulting in a different treatment of the Doppler in HH vs. VV. "Combined" does NOT refer to a combination of the polarisation channels but to baseband/geometry fusion/selection for each channel. However, even if there was a difference of a few Hz between the channels, it would not significantly degrade the usability of the products for PolInSAR Folie 61 Institut für Methodik der Fernerkundung Remote bzw. Sensing Deutsches Technology Fernerkundungsdatenzentrum Institute