Consequences of the Local Oscillator Drift model for ENVSAT ASAR

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Emil Grant
5 years ago
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CEOS Calibration and Validation Workshop

improvement of the localization accuracy

1 CEOS Calibration and Validation Workshop 2015 October 27-29, 2015, at ESA-ESTEC Consequences of the Local Oscillator Drift model for ENVSAT ASAR significant improvement of the localization accuracy Petar Marinkovic Yngvar Larsen PPO.labs Norut

2 Motivation Systematic effects in both phase and geolocalization has been observed in ENVISAT ASAR time series Credit: PhD thesis of G. Ketelaar (TU Delft) 2

3 Motivation Systematic effects in both phase and geolocalization has been observed in ENVISAT ASAR time series Credit: K. Spaans et al. Nature paper on Iceland volcanoes 3

4 Motivation Systematic effects in both phase and geolocalization has been observed in ENVISAT ASAR time series Credit: TU Delft 4

5 Presentation Structure Motivation Methodology Solution and Interpretation Recommendation and Summary 5

6 Methodology: Analysis of system parameters InSAR Geo-localization??? 6

7 Methodology: Analysis of system parameters 7

8 Re-estimation of PRF from L0 data ERS case sketch Line-fit to time-stamps Time-stamps from independent source y = ax + b Not influenced by drift L0 data input -b Timestamp value Az time [samples] Credit: Adapted from Mohr and Madsen work timing errors (2001) 8

9 Analysis of system parameters Systematic analysis of 10 years of data ~10.ooo (ten-thousand) ASAR products used All modes covered, well sampling in space and time 9

10 Analysis of system parameters: Results Systematic analysis of 10 years of data ~10.ooo (ten-thousand) ASAR products used All modes covered, well sampling in space and time 10

11 LO Model Nominal PRF / Actual PRF Systematic analysis of 10 years of data ~10.ooo (ten-thousand) ASAR products used All modes covered, well sampling in space and time 11

12 LO Model Systematic analysis of 10 years of data ~10.ooo (ten-thousand) ASAR products used All modes covered, well sampling in space and time 12

13 Influence of Drift: Back of the envelope Approximation formula: dr/yr = c/2 * (slntrngtime_far - slntrngetime_near) * corrperyr corrperyr ~ 3.87e-7 Apparent displacement correction: dr/year ~ (7.8m * 5000)*3.87e-7 ~ m Absolute positioning error: ~0.04pix/year 13

14 LO Model Coefficients in Fringe15 presentation/talk available via slideshare.net/petarmar 14

15 High-resolution Residual model 15

16 High-resolution Residual model Latitude Dependency Coefficients in Fringe15 presentation/talk available via slideshare.net/petarmar 16

17 Interpretation of results Everything we did is empirical All data, the whole mission lifetime affecte Extreme cases: absolute positioning error: 5ppm ~ 5m absolute positioning error at 1000km range (LOS) in year 2011 relative positioning error: 10 yrs * 0.04 pix/year = 0.4 * 7.8m = 3.20 m InSAR applications: effect is in the range of 15 mm/year of apparent LOS displacement (from near range to far range) 17

18 How can you be sure that LO is drifting? Point 1: Given that the ISU clock is stable (reference: Remkoo Scharroo s study on RA-2 USO Anomaly), interpretation of the observed and modelled systematic drift is that the Local Oscillator is drifting. Point 2: Also corner reflectors confirm the effect of drift (if data analysed with nominal values), and also confirmed the correction/model that is estimated from Level0 products. Reference Remkoo Scharroo: ftp://falcon.grdl.noaa.gov/pub/remko/envisat/uso-not-icu.pdf 18

19 Model validation: InSAR Btemp = 7years ~3.5 fringes 19

20 Model validation: InSAR Btemp = 7years 0 fringes 20

21 Independent Validation: DLR Example: Master acquisition Slave acquisition Original Differential-Phase Phase (FE-comp) With LO-Decay-Compensation Differential-Phase Phase (FE-comp) 21

22 Independent Validation: DLR Matrix of all interferograms (diff-phase) Original-Differential-Phase With LO-Decay-Compensation Credit: N. Adam & F. R. Gonzales, DLR 22

23 Revisiting GeoLocalization: Out of Box 23

24 Revisiting GeoLocalization: Out of Box 24

25 Revisiting GeoLocalization: +LO Corrected 25

26 Revisiting GeoLocalization: +LO Corrected 26

27 Revisiting GeoLocalization: +Atmo Corrected 27

28 Revisiting GeoLocalization: +Residual Model 28

29 ERS1/2 Digression: PRF drift 29

30 LO Drift ERS vs ASAR 30

31 InSAR application: Cross InSAR WITHOUT correction WITH correction

32 Summary LO drift is possible to describe analytically (model) almost without residues (RMS residual range error about 2cm!) The LO is really stable (compared to ERS), just a "little bit" of drift over time. GeoLocalization accuracy in RANGE down to ~20-30 cm level with all corrections applied Quality of data has been underestimated ASAR is a perfect SAR machine Acknowledgments: TU Delft for CR data Supersites Initiative for access to data archive InSAR community for independent validation efforts 32

Retrieving 3D deformation pattern of a landslide with hiresolution InSAR and in-situ measurements: Just landslide case-study

Retrieving 3D deformation pattern of a landslide with hiresolution InSAR and in-situ measurements: Just landslide case-study Zbigniew Perski (1), Petar Marinković (2), Yngvar Larsen (3), Tomasz Wojciechowski