Sentinel-1 Processor and Core Products

N. Miranda, B. RosichESA/ESRIN

Presentation layout

• S-1 Acquisition Modes (recall)• S-1 Instrument Processing Facility (IPF)• S-1 Product Family description• S-1 Product Handbook• S-1 Mission characteristics supporting InSAR• S-1 Mission Performance Center

400 Km

400 Km

250 Km

200Km

100Km

80 Km

23o

36o

S1

S6 Stripmap Mode (SM)

Interferometric Wide 

Swath Mode (IW

)

Extra Wide 

Swath Mode (EW

)

Wave Mode (WV)

19o

46o

30o45o

19o

46o

S2 S3 S4 S5

S‐1 acquisition modes

• S-1 features 4 exclusive acquisition modes

• Hight Bit Rate Modes:– Stripmap (SM)– Interferometric Wide Swath (IW)– Extra Wide Swath (EW)

• Low bit Rate Mode– Wave Mode (WV)

• HBR are single or dual polarisation

• WV is single polarisation20Km

S‐1 acquisition modes

• SM is the continuation of ERS/ASAR Image modes

• IW and EW modes relies on TOPS(1) acquisition mode combining electronic steering in elevation and azimuth:

– IWS : 3 sub-swath IW1- IW3– EWS : 5 sub-swath EW1-EW5

• WV is the continuation of ERS/ASAR WV mission but alternates swath between imagettes.

– Although using the same bandwidth as SM, WV is a LBR due to coarse spatial sampling

(1) De Zan, F.; Guarnieri, A.M.; , "TOPSAR: Terrain Observation by Progressive Scans," Geoscience and Remote Sensing, IEEE Transactions on , vol.44, no.9, pp.2352-2360, Sept. 2006

400 Km

400 Km

250 Km

80 KmS1

S6 Stripmap Mode (SM)

Interferometric Wide 

Swath Mode (IW

)

Extra Wide 

Swath Mode (EW

)

ASAR IM

19o

46o

30o45o

19o

46o

S2 S3 S4 S5

S‐1 acquisition modes

• S-1 swath versus ASAR swaths

IS1 IS2 IS3 IS4 IS5 IS6 IS7

ASAR WS/GMASAR W

S/GM

500Km

Presentation layout

• S-1 acquisition modes• S-1 Instrument Processing Facility (IPF)• S-1 Product family description• S-1 Product Handbook• S-1 Mission characteristics supporting InSAR• S-1 Mission Performance Center

S-1 IPF development activity

S-1 Instrument Processing Facility (IPF) development activity:

– Definition of algorithm for core L1 and L2 products

– Product Family definition– Product Format definition– Processor development for L1 and L2

S-1 IPF architecture

INGEST DOPPLER FOCUS

L1 L2Internal

SLC

S-1 IPF architecture

Page 9

INGEST DOPPLER FOCUS

L1 L2

S-1 algorithm definition

The IPF relies on very well established and robust algorithms for SAR processing:

•FDBAQ decoding (Huffman codes) based on binary trees

•Doppler centroid frequency (Fdc) estimation is based on:– Madsen algorithm for Fdc estimation within band– Geometry for the Doppler ambiguity (which should be zero!)

•SAR focusing: the same focusing algorithm applies to all products:– Range-Doppler + accurate Secondary Range Compression to cope

with high squint angles– Un-folding and resampling for TOPS (IW/EW)

•L1 post-processing – Radiometric corrections (range spreading loss, elevation antenna

pattern correction, denoising)– Slant to ground range projection– Multi-looking and detection– Burst and Swath merging for TOPS

S-1 IPF processing modes

The S-1 IPF supports for HBR modes two processing modes being the strip and slice processing modes:

•Strip processing:– Processing a data-take of an arbitrary size (up

to 25 min) in the same run– Results in too voluminous files; up to several

hundred of GB for SLC products– Results in too long processing time

Strip processing is the baseline for WV but not for HBR (SM, IW, EW)

10 m

in

mode SM IW EWProduct length [min] 10 10 10

SLCSingle Pol. 80 76 21

Volume [GB]Dual Pol. 159 152 43

GRD_HRSingle Pol. 6 20 5Dual Pol. 13 39 10

S-1 IPF slicing

The S-1 IPF slice processing mode:•L0 segments are split in slices of pre-defined length and sent for processing on several IPF instances•Slicing allows to:

– Have manageable product size– Distribute the processing load over several nodes– Achieve acceptable throughput (e.g. 25s of L0 IW

2-pol processed in 205 sec L1 IW SLC)•Slice processing is the baseline for all L1 HBR product types (SLC & GRD)

L1 HBR products are delivered as slices to the users.

Page 12

Sliced L1 products

5 m

in

mode SM IW EW

slice length [s] 25 25 60

SLCSingle Pol. 3.3 1.0 0.4

Volume [GB]

Dual Pol. 6.6 2.1 0.8

GRD_HRSingle Pol. 0.25 0.8 0.5

Dual Pol. 0.5 1.6 1.0

25s

S-1 IPF seamless slicing

• The slicing implemented by the IPF is such that L1 (slice) products (GRD and SLC) are of seamless quality and are directly concatenable

• Between consecutive slices there is:– No data gap or duplicated lines– No geometric, radiometric, phase

discontinuity

• Measurement data and annotations are concatenable

• Concatenation is let to the user appreciation and is not performed by the PDGS (maybe provided as part of ESA SAR toolbox)

Page 13

L1  (slice) products

Slice concatenation

L1  concatenated  products

S-1 IPF parallelization

• In addition to the slicing which contributes to distribute the processing load over different IPF nodes, each IPF node implements massive parallelisation on heavy processing steps (Doppler estimation, focusing, post-processing) which are distributed over several CPU/cores.

– The more cores are available the faster is the processing

S-1 IPF project documentation

The following items will be opened to the users in the second half of 2012:•S-1 Product Definition•S-1 Product Format Specification•S-1 Detail Processing Model

– For L1 and L2

•S-1 Auxiliary Data File format Specification•S-1 IPF interface control document•S-1 L0, L1 and L2 samples products

Table 7-5 Interferometric Wide Swath SLC Product

Product ID IW_SLC

Product Type Interferometric Wide Swath, Slant-Range, Single Look, Complex

Main Product Characteristics

Pixel Value Complex

Coordinate System Slant Range

Bits Per Pixel 16 I and 16 Q

Polarisation Options Single (HH or VV) or Dual (HH+HV or VV+VH)

Beam ID IW1 IW2 IW3

Ground Range Coverage [km] 251.8

Slant Range Resolution [m] 2.7 3.1 3.5

Azimuth Resolution [m] 21.7 21.7 21.6

Slant Range Pixel Spacing [m] 2.3 2.3 2.3

Azimuth Pixel Spacing [m] 17.4 17.4 17.4

Incidence angle [°] 32.9 38.3 43.1

Equivalent Number of Looks (ENL) 1

Radiometric Resolution 3

Product Performance Parameters

Range PSLR [dB] < -21.2

Azimuth PSLR [dB] < -21.2

Range ISLR [dB] < -16.7

Azimuth ISLR [dB] < -16.7

Distributed Target Ambiguity Ratios [dB] < -22.5

Point Target Ambiguity Ratios [dB] < -27.2

NESZ [dB] < -23.7

Channel Co-registration Accuracy [pixels] < 0.25

Absolute Radiometric Accuracy [dB] (3 sigma) 1

Relative Radiometric Accuracy [dB] (3 sigma) 0.1

Absolute Location Accuracy [m] (NRT) 7

SAR Processing Parameters

Number of Looks (range x azimuth) 1 x 1

Look overlap (range x azimuth) N/A

Range Look Bandwidth [Hz] 56.5 48.3 42.8

Azimuth Look Bandwidth [Hz] 327 313 314

Range Hamming Weighting Coefficient 0.75 0.75 0.75

Azimuth Hamming Weighting Coefficient 0.7 0.75 0.75

Table 4-1 Sentinel-1 Level 1 SLC Product Composition

File/Folder Name SM IW EW WV

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Presentation layout

• S-1 acquisition modes• S-1 Instrument Processing Facility (IPF)• S-1 Product Family description• S-1 Product Handbook• S-1 Mission characteristics supporting InSAR• S-1 Mission Performance Center

S-1 Product Family at a glance

Page 17

AcquisitionMode

L0/1/2 Producttype

GRD_FR GRD_HR GRD_MR

SM ✔ ✔ ✔ ✔ ✔IW ✔ ✔ ✔ ✔EW ✔ ✔ ✔ ✔WV ✔ ✔

GRD resolution class

Productlevel

Producttype

S-1 Product Family

LEVEL-0 PRODUCTS•(FD)BAQ encoded, unprocessed instrument source packets, with additional annotations and auxiliary information to support the processing

LEVEL-1 PRODUCTS•Slant-Range Single-Look Complex Products (SLC)

– Focused data in slant-range geometry, single look with phase and amplitude information with complete geo-reference information

•Ground Range Detected Products (GRD)– Focused data projected to ground range using an Earth ellipsoid model, detected and multi-

looked. Original satellite path direction preserved and with complete geo-reference information.

LEVEL-2 PRODUCT•Level-2 Ocean (Wind, Wave and Radial Velocities) products (OCN)

– Ocean wind field, swell wave spectra and surface radial velocities information as derived from SAR data.

L2 ocean products are available for all modes

Page 18

S-1 L1 product characteristics

(1) For GRD, the resolution given at mid-range, mid-orbit and value at mid-orbit altitude, averaged over all swaths.

(2) For SLC the resolution and pixel spacing is range dependent

(3) For SLC products, the range coordinate is in slant range. All the other products are in ground range.

(4) For GRD IW/EW, the ENL is averaged over all swaths.

Page 19

Acq. Mode Product Type Resolution

Class

Resolution 1, 2

[Rng x Azi] 3

[m]

Pixel Spacing 2

[Rng x Azi] [m]

No. Looks [Rng x Azi] ENL4

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Baseline productfor INSAR

S-1

S-1 L0product

Support

manifestXML

datageotif

data.dat

schemaXSD

S-1 L0 product format

• S‐1 product format is based on the  ESA SAFE format

• It is folder‐based product and   wraps a set of XML annotation files  and measurement data

• The number of XML files and  measurement blocks depends on  the:– product level (L0, L1, L2)– product type (SLC, GRD)– polarisation mode (single  or dual pol)

General productannotation

Instrument Source Packet(1 per polarisation)

schemaXSD

S-1

S-1 L1SLC

Annot.

Measur..

Preview.

Support

manifestXML

datageotif

datageotif

datageotif

quicklookpng

Map overlay

kmlpreview

html

schemaXSD

SM IW EW WV

1 1 1 1

1 per Pol.

1 per pol. Per swath

1 per pol. Per swath

1 per vignette

1 per Pol.

1 per pol. Per swath

1 per pol. Per swath

1 per vignette

1 1 1 1

1 1 1 1

S-1 SLC product format overview

Annot.XML

Annot.XML

Annot.XML

Annot.XML

Annot.XML

Annot.XML

Co-pol Cross-pol

datageotif

datageotif

datageotif

S-1 SLC products

• Slant-Range Single-Look Complex Products (SLC)– Phase preserving focussing using Range-Doppler + accurate Secondary Range

Compression– Single look with phase and amplitude information (16 bits I + 16 bits Q)– Data processed at zero-Doppler and provided with geo-reference information estimated from

orbit and attitude data– Imagery lying in slant-range by azimuth plane geometry– Range spreading loss and Elevation Antenna Pattern compensated– Pixel Sampling:

• Natural for SM• Resample to a common sampling in azimuth and range for IW and EW

– TOPS SLC measurement block is presented as a collection of focussed

– TOPS data are acquired with one natural burst• Longer burst than for ASAR but just enough overlap to ensure continuous ground coverage in

azimuth

– Image (geotif) and annotations (xml) are provided for each channel ( a channel being a polarisation or a sub-swath).

Page 22

schemaXSD

S-1

S-1 L1GRD

Annot.

Measur..

Preview

Support

manifestXML

Annot.XML

Annot.XML

datageotif

datageotif

quicklookpng

Map overlay

kmlpreview

html

schemaXSD

SM IW EW WV

1 1 1 1

1 per Pol. 1 per pol. 1 per Pol. 1 per vignette

1 per Pol. 1 per pol. 1 per Pol.1 per

vignette

1 1 1 1

1 1 1 1

S-1 GRD product format overview

Co-pol Cross-pol

noiseXML

calibrationXML

S-1product

Annot.

manifestXML

Annot.XML

Annot.XML

S-1 annotation datasets

calibration

calibrationXML

Annotation datasets SM IW/EW WVQuality info. ✔ ✔ ✔General info. ✔ ✔ ✔Image info. ✔ ✔ ✔Doppler ✔ ✔ ✔Geolocation ✔ ✔ ✔sr2gr GRD

N/ASwath timing N/A SLCSwath merging GRDDN to σ0 ✔ ✔ ✔DN to γ0 ✔ ✔ ✔DN to β0 ✔ ✔ ✔denoising GRD N/A

noiseXML

IW SLC: collection of focused burst per sub-swath

IW measurement data block

IW185km

IW289km

IW380km

IW GRD : debursted and sub- swath merged

Brussels

IW SLC data block

IWS SLC•Data provided in slices of 25s:

– ~9 bursts in each slice covering ~250x170km

•Data block is composed by 3 images for single pol and 6 for dual pol.•Focused burst duration: 2.75 sec roughly 20km (a fifth of an ASAR frame)

•Burst overlap: ~[405, 230, 180]m •Overlap increases in range within a sub- swath•Sub-swath overlap < 2km

Overlap~230m

2.75s

~20km

EW measurement data block

Page 27

EW1 EW2 EW3 EW4 EW5 120 Km 77Km 84Km 76Km 61Km

EW SLC data block

EW Single Look Complex:•Data provided in slices of 60s:

– ~20 bursts in each slice covering 400x400 km

•Data block is composed by 5 images for single pol and 10 for dual pol.•Focused burst duration: 3.19 sec roughly 24km (a quarter of an ASAR frame)

•Burst overlap: ~1.8Km (better than IW due to a higher azimuth steering rate) •Overlap increases in range within a sub- swath•Sub-swath overlap < 1km

3.19s

~24km

S-1 supported products

In addition to the standard L0/L1/L2 products, the PDGS generated “supported” products:•OBS product: baseline and burst synchronisation product

– Provides metadata on baseline and burst synchronisation– OBS product is sent to ngEO for supporting user interferometric

search – Allows the routine monitoring of baseline and burst sync.

performance

•PSC product: Persistent Scatter Calibration product– Allows the monitoring of the calibration constant using network of

natural stable points– Provides the mask of PSs used– The calibration constant time series for each image of the input

stack– It is an internal product could be used for preliminary PS mapping

for the INSAR users.

Page 30

Pscal Estimated NORM Constants

-3

-2

-1

0

1994 1995 1997 1998 1999 20[years]

[dB]

FlevolandMilan

Presentation layout

• S-1 acquisition modes• S-1 Instrument Processing Facility (IPF)• S-1 Product family description• S-1 Product Handbook• S-1 Mission characteristics supporting InSAR• S-1 Mission Performance Center

S-1 Product Handbook

•In parallel to the IPF development, ESA is about to start the definition of the Sentinel Product Handbook

•The PH will be developed as web-site allowing to quickly access in a consistent way basic information on the mission, instrument, PDGS, core products, algorithm and to point detailed S-1 documentation for advanced users

Presentation layout

• S-1 acquisition modes• S-1 Instrument Processing Facility (IPF)• S-1 Product family description• S-1 Product Handbook• S-1 Mission characteristics supporting InSAR• S-1 Mission Performance Center

S-1 Attitude and orbit control

S-1 provides further wrt Envisat regarding the Attitude and Orbit Control System (AOCS):

•100m orbital tube: S-1 orbits are maintained within an tube of a diameter of 100m (RMS) (at every orbital point, over any repeat cycle, during the nominal operation time)

– This ensures very limited baseline during the mission lifetime

•Total zero-Doppler steering Law: achieved by steering the platform in yaw and pitch:

– Limits the Doppler centroid to rather small values– Achieves 0-Doppler at all ground range position

•Roll Steering: reducing the updated of parameters (PRF, SWST,SWL) along the orbit

– Only one PRF over the orbit for all mode except SM/S5– SWST/SWL updated every 60s (e.g. ASAR is ~15s)

Page 34

100m

P

B

BnB//

Presentation layout

• S-1 acquisition modes• S-1 Instrument Processing Facility (IPF)• S-1 Product family description• S-1 Product Handbook• S-1 Mission characteristics supporting InSAR• S-1 Mission Performance Center

S-1 Mission Performance Center

• The S-1 Mission Performance Center is during phase E2 responsible for ensuring that the products meet or exceed the required quality performance

• The MPC is following the approach successfully put in place for Envisat that is articulated around 3 main components:

– Routine quality control (QC):– Expert Support Laboratories (ESL )providing expertise

in areas like algorithm development and evolutions, calibration and validation of core products:

– Cal/Val data data providers (CVDP)

• The MPC provides:– Systematic QC on the core products – expert user support (e.g. through eohelp)– Updated processing baseline (IPF and Auxiliary

Data Files)– Updated instrument configuration tables– Online performance report for the users

MPC

QC

CVDPCVDPCVDP

Thank You!

Page 37