calibration of sentinel-1 and terrasar-x time-series sar

Calibration of Sentinel-1 and TerraSAR-X time-series SAR data over the Queensland Corner Reflector Array, Australia

Medhavy Thankappan1, Ulrich Balss2, Matthew Garthwaite1, Christoph Gisinger3, Peter Meadows4, John Peter Merryman Boncori5, Adrian Schubert6

1Geoscience Australia, 2DLR, 3Technical University of Munich, 4BAE Systems, 5Technical University of Denmark, 6University of Zurich

Queensland Corner Reflector Array

40 corner reflectors spread over 100km x 100km

Details of individual CR sites available from the Point and Distributed Targets Database maintained by the CEOS WGCV SAR Subgroup at http://sarcv.ceos.org/targets/target_group/4/

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

Performance Testing of CRs

Signal-to-Clutter Ratio for corner reflectors derived from TerraSAR-X, RADARSAT-2, Sentinel-1A and ALOS-2 SAR imagery. Thumbnail images show the 1.5 m corner reflector response in intensity images from each SAR sensor at site 6.

# SAR images # reflectors imaged Mean SCR Std. Dev.

TerraSAR-X 11 11 49.57 3.19Sentinel-1A 3 38 32.00 2.85

RADARSAT-2 8 40 36.18 2.17ALOS-2 11 36 29.86 6.14

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

Sentinel-1A: Radiometric Performance

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

HH

Radiometric analysis of 10 HH images selected for the period from 4th June 2016 to 3rd September 2017.

Relative RCS for corner reflectors with normalisation for each acquisition.

The overall rRCS standard deviation without and with normalisation is 0.38dB and 0.32dB respectively. HH

Sentinel-1A: Radiometric Performance

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

HH

Mean and standard deviation rRCS (no normalisation) for images acquired since the start of 2016.

Good rRCS results are obtained including the three 2.5m CRs (#3, #5 & #14) for EW mode (although the STD is larger than for IW mode).

Relative RCS (dBm2) Number of Measurements

IW All Corner Reflectors -0.05±0.51 1019

IW1 All Corner Reflectors -0.06±0.51 604

IW2 All Corner Reflectors -0.05±0.52 415

IW 2.5m Corner Reflectors -0.18±0.22 77

EW 2.5m Corner Reflectors 0.21±0.67 40

Relative RCS (dBm2) Number of Measurements

IW All Corner Reflectors -0.17±0.40 126

IW1 All Corner Reflectors -0.19±0.37 73

IW2 All Corner Reflectors -0.14±0.44 53

IW 2.5m Corner Reflectors -0.20±0.07 77

VV

Sentinel-1B: Radiometric Performance

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

HH

Radiometric analysis of 10 HH images selected for the period from 8th October 2016 to 21st September 2017

Relative RCS is plotted for corner reflectors with normalisation for each acquisition.

The overall rRCS standard deviation without and with normalisation is 0.32dB and 0.28dB respectively.

HH

Sentinel-1B: Radiometric Performance

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

HH

Mean and standard deviation rRCS (no normalisation) for images acquired since the

start of the S1-B routine phase (22nd September 2016).

Good rRCS results are obtained including the three 2.5m CRs (#3, #5 & #14) for EW

mode (although the STD is larger than for IW mode). All HH polarisation.

Relative RCS (dBm2) Number of Measurements

IW All Corner Reflectors 0.09±0.42 620

IW1 All Corner Reflectors 0.14±0.40 371

IW2 All Corner Reflectors 0.01±0.44 249

IW 2.5m Corner Reflectors -0.13±0.18 47

EW 2.5m Corner Reflectors 0.38±0.74 20

Sentinel-1 ALE: Predicted – Observed Positions

Slant-range

µIW1 = -0.17 m

sIW1 = 0.30 m

µIW2 = -0.43 m

sIW2 = 1.67

µAll = -0.28 m

sAll = 1.14 m

Azimuth

µIW1 = 2.23 m

sIW1 = 0.36 m

µIW2 = 1.11 m

sIW2 = 1.02

µAll = 1.74 m

sAll = 0.92 m

Slant-range

µIW1 = -0.03 m

sIW1 = 0.21 m

µIW2 = -0.02 m

sIW2 = 0.31

µAll = -0.028 m

sAll = 0.26 m

Azimuth

µIW1 = 2.26 m

sIW1 = 0.32 m

µIW2 = 1.48 m

sIW2 = 0.24

µAll = 1.92 m

sAll = 0.48 m

Positioning results after updates (Nov.2016)Positioning results prior to updates

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

Three dates analyzed (09 Aug., 26 Sep., 08 Oct, 2015)

Sentinel-1: Absolute Location Error (ALE)Results prior to positioning update Results after update

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

Sentinel-1A IW (TOPS) products from 2014 10 30 to 2017 08 10 (56 passes in total)

TerraSAR-X / TanDEM-X: ALE

No mount model adjustment With mount model adjustment

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

TanDEM-X ScanSAR products from 2017 04 18 to 2017 09 08 - 7 passes in total

Sentinel-1 ALE: Intra-burst-dependent Range Bias

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

• Improvement of range ALE for TOPS products after implementation of a range correction1 dependent on the target intra-burst position

• Improvement of bistaticcorrection

1Rodriguez-Cassola M., Prats-IraolaP., De Zan F., Scheiber R., Reigber A., Geudtner D., Moreira A. Doppler-related distortions in tops SAR images. IEEE Trans. Geosci. Remote Sens. 2015, 53, 25–35.

Before After

Sentinel-1: Old vs New Bistatic Corrections IW / EW

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

Old OldNew New

Summary

An array of 40 CRs of 1.5, 2.0 and 2.5m sizes deployed in Queensland, Australia; some CRs individually characterised for RCS; designed to support SAR calibration

Australian CR array supporting calibration of the Sentinel-1 constellation under the ESA FRM4SAR initiative

Radiometric consistency of CRs evaluated for Sentinel-1A/B IW and EW modes, and found to be stable

Sentinel-1 geometric calibration : three independent assessments for S1 have shown improvement in ALE following updates to CR positions and other corrections

ALE for TerraSAR-X/TanDEM-X over CRs improved with use of mount model

CEOS SAR Calibration/Validation Workshop 2017, Pasadena, 7-9 November

Thank you

medhavy.thankappan@ga.gov.au