Sentinel-1A SAR Interferometry Verification Dirk Geudtner1, Pau Prats2, Nestor Yaguee-Martinez2, Andrea Monti Guarnieri3, Itziar Barat1, Björn Rommen1 and Ramón Torres1 1ESA ESTEC 2DLR, Microwave and Radar Institute 3Politecnico Di Milano
Sentinel-1 SAR Imaging Modes SAR Instrument provides 4 exclusive SAR modes with different resolution and coverage Polarisation schemes for IW, EW & SM: single pol: HH or VV dual pol: HH+HV or VV+VH Wave mode (WV): HH or VV SAR duty cycle per orbit: up to 25 min in any imaging mode up to 74 min in Wave mode 2
Sentinel-1 SAR TOPS Mode TOPS (Terrain Observation with Progressive Scans in azimuth) for Sentinel-1 Interferometric Wide Swath (IW) and Extra Wide Swath (EW) modes ScanSAR-type beam steering in elevation to provide large swath width (IW: 250km and EW: 400km) Antenna beam is steered along azimuth from aft to the fore at a constant rate All targets are observed by the entire azimuth antenna pattern eliminating scalloping effect in ScanSAR imagery Constant SNR and azimuth ambiguities Reduction of azimuth resolution due to decrease in dwell time Sentinel-1 IW TOPS mode parameters: ±0.6 azimuth scanning at Pulse Repetition Interval with step size of 1.6 mdeg. Sentinel-1A IW dual-pol image, acquired over Namibia 3
Sentinel-1A IW TOPS InSAR Repeat-pass TOPS InSAR using Interferometric Wide Swath (IW) data pairs worked on the spot 250km S-1A IW interferogram of data pair acquired 7-19 August, 2014 (2π height = 128.82m) Verification of: SAR instrument phase stability Satellite on-board timing and GNSS solution to support position-tagged commanding (OPS angle) Mission Planning system using TOPS cycle time grid points for datatake start time estimation Accurate orbit control (orbital tube) Burst synchronization 1200 km 4 Image courtesy, DLR-IMF
Datatake Start Time Estimation for Burst Synchronization Position-tag Commanding Data acquisition (repeat orbit cycle) over the same ground location uses on On-board Position Schedule execution (OPS) based on Orbit Position angle (instead of timing) Advantage: more accurate DT start time estimation no need for precise orbit prediction or frequent update of on-board command queue First imaging PRI t echo α PVT αα α start_plan Calculation of OPS angle α start_plan based on : using actual S-1A orbit position OPS angle - S-1A Reference orbit - use of an orbital point grid based on burst cycle time tt ~20 s Spacecraft Avionics converts (on-board) planned OPS angle (α start_plan ) to time (t start ) by analytical propagation of GPS PVT data t start time using SAR mode LUT t echo PVT (on-board GPS) Instrument executes measurement according to t start 5 Image courtesy, DLR-IMF
Verification of S-1A IW DT Start Time Estimation for Burst Synchronization 498 IW measurements between Aug. 7 th, 2014 (Reference Orbit reached) and Sept. 6 th, 2014 Measured performance includes: - Accuracy of the on-board conversion from OPS angles to instrument start time - Accuracy of instrument in achieving the requested start time Average = 1.32 ms Std dev = 1.28 ms Duration of IW bursts: IW1: 0.8s IW2: 1.06s IW3: 0.83s 6 Image courtesy, DLR-IMF
Burst Azimuth Spectral Alignment Burst Timing Mis-synchronization: TT dddddd Antenna Mis-pointing (squint): ff DDDD frequency k a repeat-pass burst frequency k a repeat-pass burst target at center of first burst k rot another target at center of second burst time-frequency line of target in both bursts k rot another target at center of second burst f T del shift time f DC same target in second burst f fdc shift time T del δt time-frequency line of target in both bursts target at center of first burst TOPS: ScanSAR: ff TTdddddd_sssssssss = kk aa ff TTdddddd_sssssssss = kk aa TT dddddd kk rrrrrr kk aa kk rrrrrr TT dddddd <1 ff ffdddd_sssssssss = t 0 δt kk aa ff kk aa kk DDDD = ff DDDD rrrrrr αα TOPS is more robust than ScanSAR 7
Sentinel-1A Burst Synchronization Results Estimation of along-track burst synchronization: Orbital state vectors (POD, restituted orbits) Annotated raw start azimuth time (sensing time) of the bursts Fine Co-registration using cross-correlation and ESD techniques Burst (along-track) synchronization< 2.83ms 48 InSAR product pairs 28 ascending geometry 20 descending geometry 46 in IW mode 2 in EW mode Ascending Descending Mean AT mismatch [ms] 1.17 2.83 Stdev AT mismatch [ms] 1.71 1.97 8
Sentinel-1A Burst Spectral Alignment Results Mean Doppler Centroid difference < 20 Hz due to stable attitude and antenna pointing Common Doppler bandwidth > 95% 35 30 Slave Master 25 Spectral intensity [db] 20 15 10 5 0-5 -10-15 -200-150 -100-50 0 50 100 150 200 Azimuth frequency [Hz] Satellite Pitch angle adjustment of 0.025 deg in Oct. 2014 Reduced mean Doppler centroids 9
Sentinel-1A Orbital Tube Reference orbit was reached on August 7 th, 2014 Satellite is kept within an Orbital Tube around a Reference Mission Orbit (RMO) Initially specified Orbital Tube radius of 50 (rms) equivalent to Ground-track dead-band of 60m During S-1A Commissioning: Relaxation of Ground-track dead-band to 120m Orbital Tube radius of better than 100 (rms) after adjustment of orbit Eccentricity to improve alongtrack baseline RMS of Orbital Tube w.r.t. Reference Orbit expressed in baseline coordinates 10
Sentinel-1A Orbital InSAR Baseline S-1A Commissioning results worst case orbital configuration Perpendicular Baseline < 150m 200,00 150,00 100,00 50,00 0,00-50,00-100,00-150,00-200,00-250,00 Perpendicular baseline [m] 1 9 17 25 33 41 49 57 65 73 81 89 97 105 11
Sentinel-1A SM Mode D-InSAR Earthquake Surface Deformation Mapping Demonstration of Differential and Multi-Aperture (Squint) SAR Interferometry B Pass 1 (pre-event) Pass 2 (shortly after) M6.0 South Napa Valley earthquake on August 24 th, 2014 Use of Stripmap (SM-1) data pairs acquired on August 7 th and 31 st, 2014 dr disp D-InSAR MAI (MS-InSAR) 0.2 θ inc z 0.15 x 0.1 0.05 0 Image courtesy: DLR-IMF -0.05-0.1-0.15-0.2 Image courtesy: Andrea Monti Guarnieri, POLIMI 12
Sentinel-1A IW Mode D-InSAR Earthquake Surface Deformation Mapping M7.8 Nepal earthquake on April 25 th, 2015 Sentinel-1A IW (TOPS) mode acquisitions on 17 & 29 April, 2015 M8.3 Chile earthquake on Sept. 16 th, 2015 Sentinel-1A IW (TOPS) mode acquisitions on 24 August & 17 September, 2015 Images courtesy: Contains Copernicus data (2015)/ESA/DLR Microwaves and Radar Institute/GFZ/e-GEOS/INGV ESA SEOM INSARAP study 13
Sentinel-1A Observation Scenario Tectonic and Volcanic Areas BLUE: Acquisitions in IW dual pol mode, VV+VH polarisation, every 12 days ascending and descending BLACK: Acquisitions in IW mode, VV polarisation, every 12 days ascending or descending; repeat on the same track every 24 days Stripmap mode (SM) acquisitions over selected small volcanic islands All Land and Ice masses systematically provided as IW SLC data products Includes all global tectonic/volcanic areas About 1.4 TB of IW SLC data available daily Increased sampling density over supersites outside Europe About one third of global landmass regularly covered, based on this acquisition strategy 14
Elevation Antenna Pattern Phase Correction in IPF v2.43 New IPF version 2.43 (since end of March 2015) applies a complex Elevation Antenna Pattern (EAP) correction for inter-channel phase correction in support of polarimetry applications Previous versions of the IPF did not correct for the EAP phase Interferogram between SLC data generated by previous and current IPF (2.43) version shows phase ramps in range, and eventually also phase jumps between sub-swaths. EAP is annotated in SLC product (in complex format for the new IPF version) Proposed Correction: Calculation of complex EAP for SLC data processed before end of March 2015, as outlined in TN by PDGS Alternative Correction: Undo EAP phase correction of SLC products, processed since March 2015 using the annotated complex EAP IPF 2.36 vs IPF 2.43 (EAP phase removed) Similar Issue with proposed Bistatic Correction in the IPF which implies introducing a range-dependent azimuth shift Images courtesy P. Prats, DLR azimuth range 15
Conclusions Sentinel-1 acquires systematically and provide routinely SAR data for operational monitoring tasks for Copernicus (GMES) and national EO services Using the same SAR imaging mode (instrument settings), e.g. IW mode, facilitates the build-up of long data time series for continuous observations with equidistant and short time intervals (interferogram stacks) Sentinel-1 A & B will fly in the same orbital plane with 180 deg. phased in orbit, each with12-day repeat orbit cycle Formation of InSAR data pairs having time intervals of 6-days Small orbital tube with radius of < 100m (rms) provides small InSAR baselines TOPS burst synchronization and small Doppler centroid differences enable wide-area SAR Interferometry Coherent Change Detection monitoring Collaboration with Canada s RADARSAT Constellation Mission (RCM) to facilitate multi-satellite SAR monitoring requires harmonization of data acquisition strategies 16
Backup Slides 17
Sentinel-1 Orbital Tube and InSAR Baseline S-1A & B Satellites will be kept within an Orbital Tube around a Reference Mission Orbit (RMO) Orbital Tube radius with <100m (rms) Orbit control is achieved by applying across-track dead-band control at the most Northern point and Ascending Note crossing Sentinel-1 A & B will fly in the same orbital plane with 180 deg. phased in orbit 12-day repeat orbit cycle for each satellite Formation of SAR interferometry (InSAR) data pairs having time intervals of 6-days 18