TanDEM-X Science MeetingNov. 2008

TanDEM-X Interferometric Processing Chain and SAR Products Thomas Fritz H. Breit, M. Eineder, M. Lachaise & ITP Development Team

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From Acquisitions to Products -The TanDEM-X InSAR Processing Chain Basics

Higher level processing of operational acquisition modes onlyoperational DEM generation for a specific subset of acquisition modes Systematic processing of all mission data (~400 DEM scenes / day)Data driven processingstarts when complete joint data take and all auxiliary products are available at processing system

One type of products – co-registered SSCs (CoSSCs) Processing into standardized archive products, retrieve them as delivery products via the catalogueNo processing to different product variants from raw data on user request (unlike TS-X)Monostatic processing of active channel data to MGD,GEC,EEC, …TerraSAR-X mission like products possible for restricted set of acquisitionsRaw data of experimental modes can be processed with help from DLR scientists

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TanDEM-X DEMDEM--, , Operational and Experimental Acquisition ModesClassification of acquisitions in “4D mode space”

Imaging Mode of each instrument:SMSM, SL, HS, SC, (DRA-ATI, …)Polarization Mode of each instrument:SingleSingle, Dual, Twin, DRA-Quad

Cooperative Mode of the two Instruments:bistaticbistatic, alternating bistatic, pursuit monostatic, none (TS-X mission)& experimental modesFormation Geometry:smallsmall or large along & across track separation / baseline

IM

coop

geo

pol

DEMs

Exp. Prod.

Exp. Mode

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Operational Modes Experimental Modes

TanDEM-X Cooperative Mode (of TSX + TDX sats)

Bistatic Alternating Bistatic

Pursuit Monostatic

Any

Instrument Imaging Modes Stripmap (SM) Stripmap (SM) all basic modes Any

Instrument Polarization Modes all basic modes single pol. all basic modes Any

Formation Geometry

Cross-track baselines < 4 km < 4 km < 4 km Any

Along-track baselines < 1 km < 1 km Any (large ones) Any

Processing and Products

TanDEM-X Screening L0 products

All All All raw data ( + base annotation)

DEM products SM single pol - SM single pol(fallback solution)

-

Experimental products by ITP

CoSSC+ Interferogram

2 (Co)SSCs CoSSC for SM-S best effort (@ DLR)

Experimental products by TerraSAR-X TMSP monostatic processing

TerraSAR-X L1b products* of mono-static channel

- 2 x TerraSAR-X L1b products*for all modes

best effort (@ DLR)

*: The TerraSAR-X basic product spec does not apply in terms of performance

exp.prod.

oper.prod.

TanDEM-X Acquisition Modes and Products

Slide 5

DEMDEM Acquisition & Processing Plan

Year 1: full coverage with smaller baseline

height ambiguity ~ 40 m good for moderate terrain

Year 2: repeat with larger baselineheight ambiguity ~ 30 m gives full accuracyrobust Phase Unwrapping with supporting data from first year

dual baseline PU

Year 3: more baselines & angles tofill shadow and layover regionsand support phase unwrapping of difficult areas

maximum likelihood reconstruction method

-

-

terrain slope / shadow & layover

illumination

DEM

erro

r swath shift – clapboard pattern

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Integrated TanDEM-X Processor (ITP)

ITP based on TerraSAR-X / TMSP & SRTM / InSAR-DEM heritage

modular ITP executes the complete “SAR – InSAR – DEM” processing chain, invoked in different scenarios:

1. Basic SAR data parameter screening at the receiving stations2. Fast quality check of joint TanDEM-X acquisitions3. (Bistatic) SAR focussing to co-registered SSCs (CoSSCs)

& InSAR processing & generation of Raw DEMs4. Experimental product generation for operational modes

(+ TMSP generated monostatic products)

feedback loop with triggering from Mosaicking & Calibration Processor (MCP) for optimal uniform DEM product performance (reprocessing)

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TanDEM-XScreener

receiving stationTanDEM-XScreener

raw 1 raw 2

SAR

InSAR

PU / DEM

RawDEMs CoSSCs

MCP control

MCP

final DEM(s)

control system

data driven

(In-)SARWorkflow

DEMWorkflow

systematic & operator interaction

GroundStationNetwork

Product Library DLR (PL)

WorkflowOverview

triggering of(re-)processing&customized raw DEM generation

Raw DEM(re-)processing& multi-BL support

PL

-- individualindividualdata take qualitydata take quality

-- joint (for planning)joint (for planning)

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TanDEM-X Processing Standard (By-)Products:Co-registered Single-look Slant-range Complex Products (CoSSCs)

ITP

CoSSC

SSC (“TS-X L1b”)sat1

SSC (“TS-X L1b”)sat2

common RawDEM+

DIMS PL: CoSSC Archive

CoSSC deliveryproduct

MCP internal useTanDEM-X acquisitionfor DEM generation

h

SSSLS

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ITP Bistatic Focussing

operational bistatic DEM acquisitions are restricted to limited combinations of instrument modes & close formation flight with very small bistatic angles.main complication: sync pulse processing and timing corrections

=> ITP „bistatic“ focussing uses pseudo-monostatic hyperbolic approach for DLR hybrid Chirp Scaling algorithm

primarily interferometric mission => operational SAR processing is serving the InSAR system as „pre-processing“ step

common parameter estimation for focussing & InSARphase preservation / phase synchronization co-registration of (passive) SSC to master common band & spectral shift filtering included in focussing steps

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TerraSAR-X / TanDEM-X: Interferometry Meets Stereo Radargrammetry – Terrain Adaptive Coregistration

major InSAR SW update [N. Adam]:coregistration (reference DEM & geometry. Refinement: signal correl.)

Height difference bottom-peak: 1300 m76 fringes1.18 m slant range parallax1.3 pixel misresgistration if not compensated!

= complete loss of coherence

coherencewith “classic”polynomialco-registration

not suitedfor high-res.X-bandinterferometry!!!

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Use of Maximum Likelihood Estimator in slant range geometry-> Supported by reference phases from (SRTM-)DEM & Delta-k

-> Interferogram with larger baseline is rescaled to master geometry

Phases are unwrapped using their different PDF (noisy)

Phase gradients are used for spike reduction

Δϕ [cycles/sample]-1/2 0 1/2

Ifgrm 1

with baseline B1

Δϕ [cycles/sample]

Ifgrm 2

with baseline B2

pdf of phase difference

scaling

by ∼B1/B2

multi-baseline estimate

-1/2 0 1/2

PDFs of master and „slave“broad PDF of reference phase

-> joint PDF (magenta)

Pixel 2 (neighbor)

Pixel 1

PDF of master and „slave“gradients („pixel 1“ – „pixel 2“)

joint PDF (blue) robust by MCF

correctedunwrapped

phasewrongambiguity(noise spikes)

unwrappedphase (2 BL)

ITP Dual (Multi)-Baseline Phase Unwrapping

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Delta-k Interferometry for additional PU Support

CC

0

f2f

λ

Cλ

rΔ

SAR 2

SAR 1

Differential interferogram between 2 subbands at fC ± f0Generates interferogram with “carrier frequency” 2f0 << fCFor (150MHz) standard acquisitions: delta-k hamb ~ hamb x 96.5 (9.65 GHz / 100MHz)Phase unwrapping not necessary !Successfully tested with TS-X InSAR

(R. Brcic)

Salar de Uyuni, Standard 150MHz Stripmap 14.09/06.10.2007

Two 50 MHz bandwidth subbands.

3744 m/cycle 38.8 m/cycleheight of ambiguity > ~1500m variation in topography

scaling(wrapping)

Δk phase

ESA ITT 5509- A Novel Approach for Wide-Band SAR Interferometry

f_cf_0

ambiguous

unambiguous

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Laser DEM: Gars am Inn, Bavaria5 km x 5 km, @ 5m res.

„TanDEM land“75 x 75 km

replication

Simulated TanDEM-X acquisitions (HELIX orbit, swathes, noise)

geometry simulation

Processing simulation setup

Amplitude, Layover,Shadow PhaseCoherence

InSAR simulation

resulting error map (1 – BL)

mean=0.95 mσ =1.57 m

PU errors

proc

essin

g

Dual Baseline PU

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TanDEM-X PGS InSAR Processing Test Site “Salar de Arizaro” (Argentina)

stable, highly coherent area, several interferometric pairs in different geometries(A/D, overlapping beams) acquired.

July Dec ‘07:very few temporalchanges (in blue)!

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TS-X InSAR: Single BaselinePhase UnwrappingChallenges

coherence: 0.85 baseline: 830 m !i = 39°

SRTM DEM

TS-X Interferogram (1)

height ambiguity: 7 m7 m

TS-X DEM (1)σ = 25cm !at 5m posting

……but with but with significantsignificantPU errorsPU errors

Slide 16

TerraSAR-X InSAR: 2nd Baseline coherence 2: 0.89baseline 2: 450 m > op. TanDEM-X baselinesTS-X 2nd pair

height ambiguity: 14 m14 m Differences 1st (7m hamb) – 2nd (14m hamb) DEM(atmosphere, baseline errors, fine structures, … &

PU errors in 1st DEM )

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TanDEM-X Experimental Products:Co-registered SSCs

ITP

CoSSC

SSC (“TS-X L1b”)sat 1

SSC (“TS-X L1b”)sat 2

commoncomponents

DIMS PL: CoSSC.experimental Archive

EOWEBcatalogue orders:exp. CoSSCdelivery product

TanDEM-X acquisitionfor experimental product generation

xx

InSARprocessing forbistatic SM only (e.g. dual pol)

Slide 18

Experimental Products as Co-registered SSCsCoSSC structure and format corresponds to 2 TS-X SSC L1b products (minor modifications) plus common components and annotation

product performance strongly depends on acquisition conditions but is generally slightly reduced (w.r.t. TerraSAR-X mission products):

common swath may deviate / driftcommon bandwidth processing reduces resolutionbistatic channel not radiometricallycalibrated (best effort)no add. sidelobe suppression (Hamming = 1.0), …

… but:high geometric accuracycomprehensive annotation & co-registration allow straight-forward InSARprocessingmonostatic / active channel performance may be close to TS-X products

Slide 19

Summary I – Processing Chain

Processing chain optimized for systematic generation of all raw DEM data for global HRTI-3 DEM within 2.5 years.Uniform raw DEM data performance guaranteed (multiple coverage, reprocessing) Unified processing system ITP for

global DEMcustomized DEMsexperimental products (+ TMSP)

Bistatic SAR & InSAR - DEM processing has been successfully simulated for TanDEM-X conditionsSAR & InSAR processing capabilities tested with real TS-X data

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Summary II - TanDEM-X Products

operational DEM products: see presentation by B. Wessel

operationally generated SAR products:experimental products from operational modes (co-registered complex images – “CoSSCs”)experimental mode raw data(processing with help from DLR contact scientist)TS-X mission basic products* from selected TanDEM-X raw data sets„byproduct“ of operational DEM processing chain:archive of CoSSCs from all acquisitions for DEM generation (multi-temporal global coverage)

*: TS-X basic product performance parameter specification does not apply

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