Motion compensation and the orbit restitution

Transcription

1 InSA R

2 Contents Introduction and objectives Pi-SAR Motion compensation and the orbit restitution InSAR algorithm DEM generation Evaluation Conclusion and future work

3 Introduction and Objectives L-band SAR ischaracterized by highersignal penetration, and the repeat-passsar interferometry can be achieved. High band width of Pi-SAR L band (50 M Hz) achieves higher resolution imaging and therepeat passinterferometric flights (Critical B perp is 400m and B perp <= 100m for higher coherence). As the preparation study ofsurface deformation monitoring usingthe airborne SAR,we conducted the Pi-SAR repeat passinterferometric flightsand InSAR processing. We derived an InSAR DE M, and discussed the accuracy and related problems forthefutureobjectives.

4 Pi-SAR Frequency 1.275e9 Hz Band width 50 MHz Sampling freq MHz Height 6~12Km Image swath <=15Km AD(I/Q) 8 bits ρ (R) slant 2.4 m ρ (A) 4look 3.2 m σ db NEσ0-30 db Inci. Angle 10~60 Polarimetry Full τ 10µs Pt 3.5KW Beam width(a) 8.4 degrees SIGMA-SAR processor Tottori Dune R:HH,G:HV,B:VV

5 Inertial Navigation System WGS84: Reference Earth Interface ARINC 429 LITTON AERO PRODUCTS, LTN-2001 Mk.1 made year 1989 GPS Lat Lon Height V in EW V in NS V in H 1 sec. 1 sec. 1 sec. 1 sec. 1 sec. 1 sec. Problems Ancillary Data not Synchronized with Pi-SAR Position Accuracy (GPS) INS Body Pitch Rate Body Yaw Rate Body Roll Rate Body Long. ACCEL Body Lateral ACCEL Body Normal ACCEL 64 Hz 64 Hz 64 Hz 64 Hz 64 Hz 64 Hz Pi-SAR UTC time

6 A 2 Motion Equation of G-II (I) ()= t M 1 2 ( A m N M 0 g 0 + a)+ω v ECR M 2 1 = M λ 1 M ϕ 1 M χ 1 M r 1 M p 1 M y 1 ()= A 2 () t' v t t 0 () r()= t v t' t 0 dt' +v 0 + b dt' +r 0 + c ay g roll ax g az pitch M k :rotation matrix on Euler angle ACCEL offsets a and leakage of the gravity Unknowns: a (acceleration offset), b (Initial velocity error), c (initial position error) Accelerations (g) ACCEL example Least Squared minimization -> Solution

7 Motion Equation of G-II (II) time offset GPS : 20 ms accel. attitude : 6 ms 1) Shift of the time: < 1sec 2) Parameter estimation 3) Re-generate the track 4) Calculate the horizontal and vertical shift (dh and db) 5) Interpolation and phase shift before range correlation 6) Azimuth Correlation Time offset peak Total corelation

8 Orbit errors(lat, lon, and height) Orbit corrections (dh, db) Master orbit mean(cm) std.dev dh dlat dlon second Error statistics Slave orbit mean(cm) std.dev dh dlat dlon Error statistics Real pass dh db h Ideal pass

9 Interferometry(I) Wrapped phase of master and slave images, φ, is expressed by φ = 2π λ r b ( r r t m) + b 2 r r 2 b = r m r s () z = r t R r t where r r t r m r s z R slant range, target vector master orbit, slave orbit, height, radius of the earth

10 Interferometry(II) Co-registration of two images master image x s -x m slave image x s = f (x m, y m ) y s = gx m, y m ( ) displacement in y co-registration error y s -y m Range Azimuth address direction

11 Test area : Tottori City area, including Tottori dune, river, hill side Topography : 0 m ~ 200m Observation : Oct Flight direction : East -> west Height : 8000 m Purpose : Polarimetric calibration Interferometric evaluation Averaged B perp : ~70 meter

12 Interferometry(III) Baseline analysis Baselines(B perp and B para ) dramatically change with incidence angle when tube diameter is too small. A case of B perp ~70m slave master range sample number Ground range 20 degrees of incidence angle 50 degrees

13 Sea Desert Forest Urban area Master Slave Coherence

14 Orbit correction Flat earth corrected fringe contains undesirable fringe due to the orbital error. Unwrap the raw fringe and harmonize the theoretical unwrapped model which contains three unknowns, horizontal disp.( B), vertical disp.( r), and vertical velocity disp.( v) after the least square parameterization. Ground truth data are obtained from the Digital Elevation Model of GSI (Geophysical survey of institute) and geoids height by comparing the simulated SAR image using DEM and the SAR amplitude image. Finally retune the fringe data. Least square minimization r = r 0 + v 0 t a t ( B + r)+ ( v )t

15 Processing flow 1) generate single look complex using the band width tuning 2) co-register two images using predefined GCPs 3) Generate the co-registration frame 4) Generate the raw fringe and simulated images for master/slave images 5) Calibrate the orbit error using the simulated and the SAR images 6) Unwrap the first step flat earth corrected fringe and estimate the orbital errors using the least squared error minimization 7) Regenerate the final wrapped fringe using the regenerated orbital information using the co-registration frame 8) Unwrap the above fringes and calibrate it using the GCP 9) Convert the slant range DEM to the ground range DEM.

16 Amplitude image True height Simulated image

17 Topography Flat earth corrected DEM corrected InSAR-DEM

18 Error analysis(error =InSAR DEM- DTM) Case1: Mean:2.7m Std dev.:7.4m Ocean Case2: Mean:8m Std. Dev.:15m azimuth range line line number number Case 1 Case 2

19 Three dimensional expression of the generated DEM (small area case) Tottori dune test site Ground truth DEM

20 Processing example for wider area (Tottori case) Error in the B perp Amplitude image(hh) Height error Generated DEM (Wrapped) Ground truth (GSI DEM)

21 Three dimensional view of the DEM GSI-DEM Hill Urban area In-SAR DEM

22 Conclusion and future work We have conducted the experimental study to extract the DEM using the L band repeat pass airborne SAR interferometry (Pi-SAR). One image pair flying over the Tottori dune has 70 m of B perp preserving a good coherence. DEM generated from Tottori image pair was corrected for the three unknowns, height, cross track, and cross track velocity of the restituted orbit using the ground control points given from the DSI-DEM and theoretical model. The result shows some variation in the DEM but gives an accuracy order of 2.7 meter offset and standard deviation of 7.4 meter (Best case). Motion compensation is a key component for generation of the SAR image. The required accuracy for generating image is not good enough for generating DEM. Future work: Improvement of the motion compensation using the denser ground control points (GSI-DEM) and needs nonlinear orbit correction model.

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24 Z hh Z vh Z hv Z vv = Ae 4 πr λ 1 δ 3 S hh δ 4 f 2 S vh S hv S vv 1 δ 1 + N hh δ 2 f 1 N vh N hv N vv A H R H S O SAR-P Z A V R V DT, DR1 DR2

25 CASE-1:Nov Phases Volume scattering, double bounce Cross talks (δ1, δ2, δ3, and δ4) Channel imbalances (f 1 and f 2 ) Amplitudes Phases

26 Interferometry - 苫小牧forest (HH-VV) 振幅画像 Coherence HH µ σ29.21 位相差画像 Coherence VV µ σ27.54

27 Unwrapping Methods 1)Branch cut (preserve the phase) 2)PCG, Pseudo Conjugate Gradient (slightly loose the phase) Needs for Orbital tuning using the GCPs Ground range conversion One example of unwrapped image