Precise coregistration of Sentinel-1A TOPS data. Heresh Fattahi, Piyush Agram, Mark Simons

Transcription

1 Precise coregistration of Sentinel-1A TOPS data Heresh Fattahi, Piyush Agram, Mark Simons

2 Sentinel-1A TOPS Burst N Burst 3 Burst 2 Burst 1 [Prats-Iraola et al, 212] Swath1 Swath2 Swath3 [Sakar et al, 215]

3 Sentinel-1A Opportunities and challenges Wide swath : 25 km Precise orbits High quality data Covers San Andreas Fault system Temporal resolution : 12 days (currently they mainly acquire 24 days) Will improve with Sentinel-1B linearly varying Doppler centroid frequency. Very precise coregistration is Required. Accuracy better than.1 pixels Can we push ESA to acquire highest temporal resolution possible for SAF?

4 Master Swath (can be multi-slice) DEM Slave Swath (can be multi-slice) Full burst Overlap regions Sync between 3 swaths Pixel-by-pixel Lat, Lon, HAE Pixel-by-pixel Range, Azimuth offsets Coarse Resampled slave bursts Image used Metadata only Constant range offset (ampcor) Burst-by-burst Coarse Interferogram Constant azimuth offset (ESD) Burst-by-burst Fine Interferogram Merge bursts & swaths Fine Resampled slave bursts Pixel-by-pixel Range, Azimuth offsets

5 Coregistration with geometry Range-Doppler equations: Time-Range coordinate Using Orbit & DEM Coordinate on ground Needs precise Orbits (few cm). Doesn t Need Accurate DEM (few 1s of m vertical acc is fine).

6 Coregistration with geometry Impact of DEM on coregistration Bperp = ~ 1 m DEM Impact on phase -.5 to.5 mis-registration (pixels) mis-registration (pixels) Azimuth Height m. Range Height m

7 Coregistration with geometry (orbit + DEM). 1 burst

8 Coregistration with geometry (orbit + DEM). + 1 burst Constant Azimuth misreg =.3 pixel

9 Geometrical coregistration Geometrical coregistration + constant azimuth misregistration

10 Impact of azimuth misregistration on one interferogram: ~.3 pixels ~.4 radians ramp in azimuth direction for each burst Correction strategy: a) geometrical coregistration (accuracy.1 pixel) b) coarse interferograms at the burst overlaps c) Estimating the azimuth misregistration using Enhanced Spectral Diversity Final coregistration accuracy better than ~.1 pixel

11 Enhanced Spectral Diversity (fine azimuth misregistration) Burst Overlap Master Slave Master Slave Overlap differential interferogram: sd = (M top. S * top ).(M bot. S * bot ) * Δf Δt φ sd = 2πΔf Δt : Spectral separation of the two sublooks (can be computed from geometry) : Azimuth misregistration (in seconds)

12 Enhanced Spectral Diversity (fine azimuth misregistration) } 21 burst overlap interferograms -.4 median = -.3 pixel.4 az offsets } 21 burst overlap coherence (24 days) } 21 burst overlap coherence (96 days) Accuracy of estimated misregistration is a function of the coherence This can be a problem for stack processing. Low coherence between SLCs with long temporal separation

13 Coregistration of a stack of SLCs (required for stack processing): Estimatiing the azimuth misregistrations for small baseline pairs and inverting for the stack misregistrations δt = AδT Bperp Small baseline pair misregistrations Misregistrations Of all dates relative to the stack Master date Time Geometrical coregistration for the stack is the same as the single pair. (Offsets of all dates relative to a master date) Enhanced Spectral Diversity : For single pair (master-slave) only doppler centroid rate of the slave SLC is required to calculate the spectral separation. For master-slave pairs (in stack) the doppler centroid of both master and slave SLCs are required to calculate the spectral separation.

14 Impact of the azimuth misregistration on the time-series Estimated azimuth mis-registrations: : : : : : : : : : : : : : : : : [mm] Few mm ramp across one burst

15 Elevation Antenna Pattern Without correction After EAP correction Only observed in pairs constructed from SLCs processed with different IPF versions

16 Tajikistan earthquake M7.2, Dec Processed interferogram is available through UNAVCO 47 km

17

18 1 year time-series 16 images Creep [mm/yr] -2 2

19 Back up slides

20