Sentinel-1A Product Geolocation Accuracy: Beyond the Calibration Phase

Transcription

1 Sentinel-1A Product Geolocation Accuracy: Beyond the Calibration Phase 27 October 2015 Adrian Schubert, David Small (UZH), Nuno Miranda (ESA-ESRIN), Dirk Geudtner (ESA-ESTEC), Erich Meier (UZH) Page 1

2 Data Acquisition Overview Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 Mainly SM SLC Swiss test sites Mainly IW SLC Australian test site CR array Page 2

3 Definition of Absolute Location Error (ALE) Page 3

4 Definition of Absolute Location Error (ALE) az Mean ± standard deviation rg Page 4

5 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 ~ 0.5 m ~ 3-4 m (1-way) ~ 0.1 m Page 5

6 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Mean ± standard deviation: Δrg ± 0.32 m Δaz 1.79 ± 0.34 m Corrections made: + plate tectonics & solid Earth tide Page 6

7 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Mean ± standard deviation: Δrg 1.24 ± 0.07 m Δaz 1.79 ± 0.34 m Corrections made: + plate tectonics & solid Earth tide + atmospheric path delay Page 7

8 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 Page 8

9 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 up to ~ 0.5 m (SM) PT Page 9

10 & bistatic residual "effects" for a point target From the Sentinel-1 Product Specification 2/9 Table 6-65: Data Type - imageinformationtype productfirstlineutctime: Zero Doppler azimuth time to the mid-slant range of the first line of the image [UTC]. When bi-static correction is performed (bistaticdelaycorrectionapplied set to true) during processing the time annotated is the time of the imaging of the ground. When bi-static correction is not performed the time annotated is the time of the reception of the echo. Azimuth line time is (originally) the UTC time of the received mid-range echo (shifted to zero Doppler by IPF) Page 10

11 & bistatic residual "effects" for a point target IPF corrects the azimuth "bistatic" effect by shifting the mid-range echo receive time to zero-doppler (i.e. considering the slant-range travel time ("fast time") to/from the mid-range position) Minimises "out-of-the-box" errors Requires a "residual correction" for geolocation targets relative to the mid-range correction Page 11

12 & bistatic residual "effects" for a point target Residual error for a general point target PT at range sr PT azimuth sr mid sr near sr PT sr far zero Doppler (sr PT ) zero Doppler (sr mid ) PT zero Doppler (sr near ) fasttime PT Page 12

13 & bistatic residual "effects" for a point target Residual error for a general point target PT at range sr PT azimuth sr mid sr near sr PT sr far Nominal bistatic correction (IPF) zero Doppler (sr PT ) zero Doppler (sr mid ) PT fasttime PT Page 13

14 & bistatic residual "effects" for a point target Residual error for a general point target PT at range sr PT azimuth correction for PT sr mid sr near sr PT sr far Nominal bistatic correction (IPF) zero Doppler (sr PT ) zero Doppler (sr mid ) PT fasttime PT Page 14

15 & bistatic residual "effects" for a point target Page 15

16 & bistatic residual "effects" for a point target az time error [s] = (fasttime PT - fasttime mid ) / 2 az ALE residual error [m] = (az time error [s]) x platform velocity [m/s] Needs to be subtracted from azimuth prediction to correct it Page 16

17 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Mean ± standard deviation: Δrg 1.24 ± 0.07 m Δaz 1.78 ± 0.17 m Corrections made: + plate tectonics & solid Earth tide + atmospheric path delay + bistatic residual Sentinel-1A Product Geolocation Accuracy: Commissioning Phase Results (A. Schubert, D.Small, N. Miranda, D. Geudtner, E. Meier); Remote Sens. 2015, 7, ; doi: /rs Page 17

18 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 up to ~ 0.5 m (SM) PT Page 18

19 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 ~1.2 m rg = 0 Page 19

20 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Mean ± standard deviation: Δrg 0.00 ± 0.07 m Δaz 1.78 ± 0.17 m Corrections made: + plate tectonics & solid Earth tide + atmospheric path delay + bistatic residual + SWST bias Page 20

21 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 ~1.2 m rg = 0 Page 21

22 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 Definition of the TOPS SLC deramping function for products generated by the S-1 IPF (N. Miranda); COPE-GSEG-EOPG-TN , Iss 1 / Rev 2, Page 22

23 IW SLC product geolocation: Improvement using deramped & demodulated vs. phase detected samples Page 23

24 IW SLC ALE using detected mosaics (25 products) IW SLC products over Torny-le-Grand: ALE for detected vs. demodulated complex mosaics IW SLC ALE using demodulated mosaics (25 products) Target in IW2 - swstbias (from AUX_INS) is zero in all cases (pre-may 2015) - question currently under investigation: IW3 geolocation offset compared with IW2 (no CRs in IW1 to compare with; but one product is available with a transponder in IW1/2 overlap zone: a relative az. shift of 2.2m was observed, suggesting a possible beam-dependent effect) Target in IW3 Page 24

25 IW SLC ALE using detected mosaics (25 products) IW SLC products over Torny-le-Grand: ALE for detected vs. demodulated complex mosaics IW SLC ALE using demodulated mosaics (25 products) - Lower range and azimuth ALE spread using demodulated phase Dsc Asc Dsc Asc Target in IW3 Page 25

26 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 Page 26

27 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 up to ~ 2 m (IW) PT Page 27

28 Australia Queensland array: ALE estimates for IW SLC time series ( ) Page 28

29 IW SLC products over Queensland (N.B. complex demodulated phase) Products processed at UZH Mar 6 Oct 8 (merged); IPF v2.36, v2.43, v2.45, v2.51, v2.53 (25 products) residual correction APD correction SWST bias = (AUX_INS) (16 points) ALE rg: ± 0.09 m ALE az: 4.01 ± 0.63 m (16 points) ALE rg: 3.72 ± 0.12 m ALE az: 3.12 ± 0.29 m Page 29

30 Australia Queensland array: ALE estimates for 7 SM SLC products ( ) Page 30

31 SM SLC products over Queensland SM SLC (beams S1 and S4); IPF v2.53 residual correction APD correction SWST bias = (AUX_INS) (3 points) ALE rg: ± 0.12 m ALE az: 3.50 ± 0.03 m (3 points) ALE rg: 3.68 ± 0.21 m ALE az: 2.26 ± 0.04 m Page 31

32 SM SLC products over Queensland SM SLC (beams S1 and S4); IPF v2.53 residual correction APD correction SWST bias = (AUX_INS) 2.0m CRs 2.5m CRs Page 32

33 SM SLC products over Queensland SM SLC (beam S4, ); IPF v2.53 residual correction APD correction SWST bias = (AUX_INS) 2.0m CRs 2.5m CRs Page 33

34 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 up to ~ 2 m (IW) PT Page 34

35 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) Launch End cal phase (SM) SWST bias TOPS deramping (TOPS) Apr 14 Jan 15 Mar 15 May 15 Aug 15 Oct 15 Page 35

36 Current best estimate of ALE for SM SLC products (based on time series over Swiss test sites) (SM) SWST bias TOPS deramping (TOPS) Mar 15 May 15 Aug 15 Oct 15 Towards S1-B Page 36

37 Geolocation Accuracy Summary All products residual correction now improves azimuth ALE by up to ~0.5 m (SM) ~2 m (IW) or ~3 m (EW) Sub-pixel accuracy and precision achieved for SM and TOPS modes Stripmap SLC products Current ALE extremely low (rg 7 cm, az 17 cm) when external influences mitigated TOPS SLC products deramping & demodulation improve geolocation measurably Geolocation accuracy already very high (esp. given coarser sampling compared with SM); improvement still expected Page 37

38 Geolocation Accuracy Summary Queensland array: Unique target configuration permits interesting long-term analysis Still to do: More detailed reflector-specific ALE statistics A careful repeat survey would likely improve the agreement between the targets (reduce ALE "cloud" size) Page 38

39 Near-Term Outlook Plan on investigating TOPS sub-pixel effects how to best implement APD modeling automatically & globally for S1-B Looking forward to S1-B! This study was funded in part by ESA-ESTEC contract /14/NL/MP/ab and subcontract CLS-DAR-DF from the Sentinel-1 Mission Performance Center. This paper contains modified Copernicus Sentinel data from 2014 to Page 39 Page 39

40 Page 40

41 Extra materials Page 41

42 Torny-le-Grand SM SLC: updated ALE estimates using products processed with IPF v2.53 and internal OSVs (better GNSS solution) Page 42

43 SM SLC products over Torny-le-Grand (old result) SM SLC (beams S2, S5 and S6) - bistatic residual correction applied SM SLC ALE Mean ± standard deviation: Δrg ± 24.6 m Δaz ± 23.0 m

44 SM SLC products over Torny-le-Grand (new result) SM SLC (beams S2, S5 and S6) - bistatic residual correction applied SM SLC ALE Mean ± standard deviation: Δrg 0.30 ± 1.62 m Δaz ± 5.03 m

45 Clear improvement for IPF v2.53 compared with v2.34 & v2.35 (as expected) Page 45

46 IW SLC products over Dübendorf: location of CRs for typical ascending products Asc. with CR in beam IW2 (S1A_IW_SLC 1SDV_ T171503_ T171538_003237_003BCA_59A4.SAFE) CR IW1 IW2 IW3 Asc. with CR in beam IW3 (S1A_IW_SLC 1SDV_ T172303_ T172330_003135_0039A3_D791.SAFE) CR

47 IW SLC products over Queensland (N.B. complex demodulated phase) Products processed at UZH Mar 6 - Apr 23; IPF v2.36 (1 product), v2.43 (4 products) residual correction APD correction SWST bias = 0 (AUX_INS)

48 IW SLC products over Queensland (N.B. complex demodulated phase) Products processed at UZH May 5 Oct 8; IPF v2.43, v2.45, v2.51, v2.53 (20 products) residual correction APD correction SWST bias = (AUX_INS)

49 SM SLC products over Queensland Overall SM scatter "shape" similar to IW SLC scatter Confirms that surveyed positions are the largest source of ALE standard deviation Larger CRs (2.0m and 2.5m) are outliers (survey differences compared with the 1.5m CRs?) Mean azimuth ALE is ~2m lower for SM (mean ~2.4m) than for IW (mean ~4.4m); reason needs to be investigated Page 49

50 SM SLC products over Queensland Most recent S4 product ( ) shifted ~2.5 m relative to others. Why? Already checked: APD compensation: done in the same way for all products target-specific problems (e.g. water or bird "doings" in CR) not possible since all targets affected swstbias difference: none, since same AUX_INS file used to process all products Page 50