Generation and calibration of high resolution DEM from single baseline space-borne interferometry: the splitswath

Transcription

1 Geeratio ad calibratio of high resolutio DEM from sigle baselie space-bore iterferometry: the splitswath approach Davide Giudici Adrea Moti Guarieri, Daiele Mapelli, Fabio Rocca

2 Outlie Itroductio: sigle pass Digital Elevatio Models (DEMs) geeratio missios Urba ad peri-urba DEMs A sigle-pass Ka-bad iterferometer cocept Vertical accuracy performace model the eed of baselie calibratio The split-swath approach for efficiet calibratio

3 DEM geeratio ad Sigle pass iterferometry The geeratio of Digital Elevatio Models (DEMs) through sigle pass SAR iterferometry is a well kow applicatio It takes advatage of the almost ull target de-correlatio SRTM ad TANDEM-X missios are successful examples kellylab.berkeley.edu Is it possible (ad useful?) to go beyod this accuracy with SAR DEMs?

4 Urba ad peri-urba [ruer, 010]: TerraSAR-X VHR data are ot eough, horizotal resolutio < 3 m ad vertical < 1 m is eeded to cout floors. [Cellier, 006]: Icidece agle is critical: observatios is limited by shadow: if layover is solved by polarimetry, with 4, urba roads are ivisible if L<0.88H [Allebach 010]: I urba areas, very high resolutio optical sesors provide aalogous results, especially if flood traces are represeted by apparet water. SAR results i rural ladscape are relevat; this pertiece is ot observed i urba areas

5 PS urba DEMs [Perssi 008]: High 3D resolutio ca be achieved by repeat pass iterferometry over PS (< 1 m from coarse resolutio ERS) [Adam igarss 08] with possible layover separatio due to tomography [Reale 011] ad polarimetry [Perissi 007] PS + radargrammetry [Adam 010] at very «high» desity ( PS/Km, [Gerhart 010]) Higher desity ca oly be achieved with fier resolutio ad without temporal decorrelatio

6 Sigle pass iterferometer at Ka-bad We cocetrate o a sigle-pass iterferometer i Ka bad (35 GHz) Goal sigle look resolutio: < 1x1 m oom legth is paramout to maitai low height of ambiguity. Need >0 m to have q < 60 m oom Ka bad.5 ich from SANDIA Natl Labs

7 11 th May 011 Approach to performace models defiitio 3D SAR locatio equatios 1.The rage equatio:.the Doppler equatio: The followig simplificatios are itroduced: 1. Igore bistatic delay. Small errors (liearizatio) 3. Zero Doppler poitig : The problem ca be hadled i a simplified D geometry S 3.The iterferometric equatio: S M S y z z r P r x O P(0, q) y '

8 Vertical accuracy model The simplified iterferometric equatios are obtaied: Liearizatio close to the optimal soultio leads to the 3D locatio error, due both to measures (x) ad geometry (θ) Positio covariace si 4 q r 1: error due to phase : term due to ukow geometry: parallel ad ormal baselie si si 4 p p p r r

9 Phase variace model Assumig that the SAR image has high resolutio compared to the fial DEM resolutio. The phase variace is computed with the CR formula, valid for high umber of looks: With this formula, the phase variace depeds o: 1. The total coherece (). The total umber of idepedet looks (NL)

10 Total coherece computatio Five cotributios are cosidered: - Thermal oise - Ambiguity - Volume - Coregistratio error - Quatizatio error NESZ= -15 d 1 amb [-] Ambiguity decorr, AASR: -15d AASR: -0d AASR: -5d RASR [d] thclut [-] Thermal oise decorr, vol [-] Volumetric decorr, SNCR: 10d SNCR: 15d SNCR: 0d sigma 0 [d] Ext. coeff: 1.00e-001d/Km Ext. coeff:.00e-001d/km Ext. coeff: 3.00e-001d/Km Ext. coeff: 4.00e-001d/Km Heigth of ambiguity [m]

11 Target urba DEMs I the followig aalysis, two target-dem cases have bee cosidered, correspodig to two sigle pass iterferometry systems (Stripmap ad TOPSAR). UoM Iitial value (SOW) Sigle-pass iterferometry HRTI+ Sigle-pass iterferometry HRTI++ Remarks Wavelegth m Correspodig to GHz Acquisitio mode - High resolutio mode TOPSAR -swaths Stripmap Output DEM resolutio Output DEM height accuracy 1 m x m 1 x 1 6x 6 4 x 4 >HRTI-3 m >HRTI-3 Orbit altitude Km Average orbit altitude Look agle deg Terrai slope deg HRTI+: average case HRTI++: aalysis from Polimi Assumed as margi (Impact o spectral shift) Topography extet m < Assumed as margi Calibratio DEM H-resolutio Calibratio DEM V-res 1 m SRTM DEM m SRTM; DEM 11

12 Height accuracy with perfect geometry This is the cotributio to overall height retrieval accuracy that caot be compesated through calibratio DEM retrieval error 1 [m] Total Coherece: 0.7 Total Coherece: 0.8 Total Coherece: 0.9 HRTI3: q =0.86m X: 144 Y: NL=36: DEM resolutio 6x6 m Iterf. resolutio: 1 m Total umber of Looks NL=36: DEM resolutio 1x1 m Iterf. resolutio: 4 m NL=144: DEM resolutio 1x1 m Iterf. resolutio: 1 m

13 Height accuracy with geometry errors Parallel baselie calibratio error 1 [ m] The ormal ad parallel baselies have to be kow with a accuracy i the order of 10-5 m DEM retrieval error 1 due to p ad [m] 0.86/0.6 m Normal baselie calibratio error 1 [ m] p Normal baselie: 4 p r si r si - Error proportioal to the elevatio: q q e Parallel baselie: - error icreasig with distace («DEM rotatio»), - idepedet o the elevatio: r si q p Calibratio eeded! p 13

14 aselie calibratio methods aselies ca be calibrated cosiderig kow topography cotrol poits: - Referece DEM (e.g. SRTM) - A flat surface (the sea level) - A least squares method is cosidered to compute the calibrated baselie - Two calibratio scearios are cosidered: 18 km 18 km 75 km Cotiuous swath Split swath

15 aselie calibratio accuracy compariso Parallel baselie calibratio error 1 [m] Sigle swath (dashed lie) Split swath (solid lie) Parallel aselie X: 10.5 Y:.95 Sub-swath size: 10 Km Sub-swath size: 15 Km Sub-swath size: 0 Km X: 0 Y: 3.5 Normal baselie calibratio error 1 [m] Normal aselie Sigle swath (dashed lie) Sub-swath size: 10 Km Sub-swath size: 15 Km Sub-swath size: 0 Km Split swath (solid lie) Azimuth legth [Km] Azimuth legth [Km] Split swath allows calibratio withi a legth of 5 Km With cotiuous swath more tha 0 Km are eeded: it is ot the preferred solutio 15

16 Calibratio methods compariso I the table the two calibratio methods are compared, idetifyig the first pros ad cos. Calibratio method PRO CONS Cotiuous swath Split swath -Wider cotiuous swath - Smaller beam elevatio agle - Allows doig the calibratio i short legth: large lowfrequecy boom errors are tolerated - A log observatio is eeded to calibrate ad models for vibratio -No wide cotiuous swath -High beam elevatio capability required

17 DEM retrieval accuracy budget summary (HRTI+) Item UoM value Wavelegth m Output DEM resolutio mxm 6 x 6 Slat rage Km 60 Look agle deg 35 Terrai slope deg 5 Topography extet m 9000 Volume depth m 0.9 Extitio coefficiet d/m 0. Referece DEM resolutio m 90 Referece DEM 1 m 5 SNCR d 30 NESZ d -16 Sigma0 d -4 * AASR d -0 RASR d -0 SQNR d 0 Image size across track Km 18 Azimuth calibratio legth Km 5 Normal baselie m Rage badwidth MHz 500 Azimuth resolutio m Heigth of ambiguity m Coregistratio error m Item UoM value Coherece clutt+thermal Coherece volume Coherece coreg Coherece ambiguity Coherece quatizatio Total coherece Iterferogram gr.rg.resolutio m 0.6 Number of looks Phase variace rad^ Height error std with perfect geometry Parallel baselie std after cal Normal baselie std after cal Height error std due to geometry oly m m 16 m 1.0 m 0.34 Total height error std m 0.76 *Ulaby F.; Moore R.; Fug A., Microwave Remote Sesig, Active ad

18 DEM retrieval accuracy budget summary (HRTI++) Item UoM value Wavelegth m Output DEM resolutio mxm 4 x 4 Slat rage Km 556 Look agle deg 5 Terrai slope deg 5 Topography extet m 9000 Volume depth m 0.9 Extitio coefficiet d/m 0. Referece DEM resolutio m 90 Referece DEM 1 m 5 SNCR d 30 NESZ d -16 Sigma0 d -4 * AASR d - RASR d - SQNR d 0 Image size across track Km 9 Azimuth calibratio legth Km 5 Normal baselie m Rage badwidth MHz 500 Azimuth resolutio m 1 Heigth of ambiguity m Coregistratio error m Item UoM value Coherece clutt+thermal Coherece volume Coherece coreg Coherece ambiguity Coherece quatizatio Total coherece Iterferogram gr.rg.resolutio m 0.88 Number of looks - 18 Phase variace rad^ Height error std with perfect geometry Parallel baselie std after cal Normal baselie std after cal Height error std due to geometry oly m 0.58 m 16 m 1.0 m 0.34 Total height error std m 0.68 *Ulaby F.; Moore R.; Fug A., Microwave Remote Sesig, Active ad

19 Coclusios The prelimiary models to assess vertical accuracy for a sigle-pass, high resolutio, Ka-bad iterferometer have bee studied. Modelig method is based o small error assumptio (liearizatio) It results that the vertical accuracy is the sum of two mai cotributios: A. Error due to phase variace o-calibrable. Error due to ukow geometry calibratio NEEDED Accuracies better tha HRTI3 ca be obtaied With the split swath calibratio techique, sufficiet accuracy o the baselie calibratio ca be achieved i less tha 1s