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Guide to Sentinel-1 Geocoding

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Guide to Sentinel-1 Geocoding Issue: 1.10 Date: 26.03.2019 Guide to S-1 Geocoding Ref: UZH-S1-GC-AD Page 1 / 42 Guide to Sentinel-1 Geocoding Supported by: à Versions up to 1.05: Sentinel-1 Mission Performance Centre (S1MPC) ESRIN Contract No. CLS-DAR-DF-13-041 à Versions 1.06 through 1.10: Subcontract from Telespazio/Vega IDEAS+ Authors: David Small & Adrian Schubert Distribution List Name Affiliation Nuno Miranda ESA-ESRIN David Small UZH-RSL Adrian Schubert UZH-RSL Peter Meadows BAE Guillaume Hajduch CLS Issue: 1.10 Date: 26.03.2019 Guide to S-1 Geocoding Ref: UZH-S1-GC-AD Page 2 / 42 Document Change Record Issue Date Page(s) Description of the Change 0.5 11.07.2017 all Initial Draft Issue 0.7 14.08.2017 Extended discussion of S-1 bistatic residual correction Replaced Figure 5 with S-1 example 0.9 25.08.2017 Corrected some corrupt equation objects; formatting fixes; clari- fied sections on azimuth bistatic corrections. Various minor clar- ifications and corrections spanning the document. 0.91 01.09.2017 Minor edits in response to comments from P. Meadows (BAE) 0.92 01.09.2017 UZH logo added; small correction to Fig. 1 0.95 01.02.2018 New section 4.6.8 added, comparing “out-of-the-box” S-1 prod- uct geolocation accuracy with UZH post-processed accuracy. 1.0 13.02.2018 Edits made to address comments from ESA. 1.01 01.03.2018 Added discussion in section 4.6.8; Final edits made to text flow; added column with ALE requirement to Table 11 and references to S-1 Product Definition and two recent technical notes on pre- cise geocoding. 1.02 03.05.2018 Updated section 4.6.8 with ALE scatterplots after the recent im- plementation of an additional azimuth timing correction (text, figure and table updates). Reference [12] added to replace an earlier reference by Aresys that was less accessible. 1.03 09.05.2018 Comments added naming the subtler corrections made to the precise ALE estimates in section 4.6.8 (with reference to [12]). 1.04 13.06.2018 Updated section 4.6.8 with ALE scatterplots including additional azimuth timing correction for TOPS products (text, figure and table updates). 1.05 10.07.2018 Updated section 4.6.8 with additional ALE estimates over Aus- tralian Surat array, as well as a site overview and discussion. Added references to further papers. Issue: 1.10 Date: 26.03.2019 Guide to S-1 Geocoding Ref: UZH-S1-GC-AD Page 3 / 42 1.06 10.02.2019 Updated Table 10 and section 4.7.3 to reflect the S-1 IPF's actual behaviour concerning the bulk bistatic correction: the correction is made with reference to the near-range sample, not the mid- range sample as previously assumed. For TOPS, it is the near- range sample of the mid-swath (IW2 or EW3). Added new section 4.6 briefly describing the effect of APD, frame shift and SET on reference target positions. Added reference to 2012 JoG paper. Added section 4.7.10 (incl. Table 11) summarising the applica- bility of corrections to product types. 1.07 12.02.2019 Fixed formatting problem in the header (Issue and date). Format- ting adjustment p. 37-38. 1.08 05.03.2019 Added sections 4.7.4 and 4.7.5, briefly describing the remaining corrections needed to obtain improved post-processing estimates, as shown in scatterplots (Figure 6 and Figure 7). Updated Table 11 to include new effects, as well as section 4.7.11 to account for the update. 1.09 22.03.2019 Fixed previous error in Table 12 that had been caused by a “track changes” bug. Corrected an erroneous reference in section 4.7.4 (first published description of the ITC). 1.10 26.03.2019 Fixed broken cross-references. Clarified wording in sections 4.6.3, 4.7.4, 4.7.5, 4.7.10, and 4.7.11. Added further entries to Table 2. Clarified text in chapters 3 and 4; added GRDM to section 4.1. Added funding support clarifications on title page. Issue: 1.10 Date: 26.03.2019 Guide to S-1 Geocoding Ref: UZH-S1-GC-AD Page 4 / 42 TABLE OF CONTENTS 1 INTRODUCTION ................................................................................................ 7 1.1 SENTINEL-1 PRODUCT TYPES FOR GEOCODING ......................................................... 7 1.2 ACRONYMS ............................................................................................................... 8 1.3 SENTINEL-1 PRODUCT DATA TYPES .......................................................................... 9 2 REQUIRED SAR GEOMETRY PARAMETERS .......................................... 10 3 SYSTEM DESIGN ............................................................................................. 12 4 SAR GEOCODING IN DETAIL ...................................................................... 14 4.1 INGESTION TO ANNOTATED RADAR GEOMETRY RASTER ..................................... 14 4.1.1 Product Input ...................................................................................................... 14 4.1.2 Detection and Multi-looking ............................................................................... 16 4.2 DEM INPUT AND MAP GEOMETRY INITIALISATION ................................................ 17 4.3 ORBITAL STATE VECTORS ...................................................................................... 18 4.3.1 State Vector Input ............................................................................................... 18 4.3.2 State Vector Initialisation and Timing ................................................................ 19 4.4 RADAR GEOMETRY IMAGE INPUT ......................................................................... 19 4.5 ORTHORECTIFICATION / DEM TRAVERSAL ............................................................. 20 4.6 GEOPHYSICAL FINE PERTURBATIONS ON THE TARGET POSITION .............................. 22 4.6.1 Atmospheric path delay (APD) ........................................................................... 22 4.6.2 GPS reference frame shift caused by plate tectonics ......................................... 22 4.6.3 Solid Earth Tide (SET) ....................................................................................... 23 4.7 POINT GEOLOCATION .............................................................................................. 23 4.7.1 Range-Doppler (RD) Geolocation ...................................................................... 23 4.7.2 “Bistatic” Azimuth Bias Correction ................................................................... 27 4.7.3 “Bistatic Residual” Azimuth Bias Correction .................................................... 29 4.7.4 Instrument Timing Correction ............................................................................ 29 4.7.5 Burst-Position Dependent Timing Corrections (TOPS Mode) ........................... 30 4.7.6 Ground Range IndeX Computation (when necessary) ........................................ 30 4.7.7 Resampling ......................................................................................................... 32 4.7.8 Calculation of Absolute Location Error (ALE) .................................................. 33 4.7.9 Impact of Local Height Variations and Ellipsoid- vs. Terrain-Geocoding ........ 34 4.7.10 Applicability of Corrections to S-1 Products ..................................................... 34 4.7.11 Sentinel-1 “Out-of-the-BoX” vs. Precise Geolocation Accuracy ....................... 34 4.8 OUTPUT ANNOTATIONS ........................................................................................... 39 5 REFERENCES ................................................................................................... 41 Issue: 1.10 Date: 26.03.2019 Guide to S-1 Geocoding Ref: UZH-S1-GC-AD Page 5 / 42 LIST OF TABLES Table 1: Sentinel-1 Product types that may geocoded using the methods described in this report ............. 7 Table 2: Document Acronyms ..................................................................................................................... 8 Table 3: Sentinel-1 data type primitives ...................................................................................................... 9 Table 4: Sentinel-1 product parameters required for range-Doppler geocoding ........................................ 10 Table 5: Sentinel-1 State Vector Parameters required for range-Doppler geocoding ................................ 11 Table 6: Sentinel-1 Slant/Ground Range Parameters additionally required for range-Doppler geocoding of GRD products ........................................................................................................ 11 Table 7: Geometry parameters required for geocoding different Sentinel-1 product types; names of parameters referring to multi-looked images are in italics. ......................................................... 15 Table 8: Cartographic & Geodetic Coordinate Systems ............................................................................ 18 Table 9: External Sentinel-1 State Vector Product Types .......................................................................... 19 Table 10: Azimuth timing conventions in ASAR and Sentinel-1 SLC products ......................................... 28 Table 11: Applicability of geolocation corrections to level-1 Sentinel-1 products (N.B. some effects may influence geolocation even if they cannot be corrected in practice) .................................... 35 Table 12: ALE estimates over Swiss time series for SM, IW and EW mode SLC products, with and without post-processing timing corrections. The left column represents typical “out-of-the- box” ALE that may be expected after applying the geolocation algorithm and corrections described
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