Copernicus Sentinel-2 Global Mosaic

www.s2gm.eu Copernicus Sentinel-2 Global Mosaic

Copernicus Sentinel-2 Global Mosaic

REDDCopernicus Stakeholder Workshop June 2019

WEVERS, JAN (1); BRANDT, GUNNAR (1); KIRCHES, GRIT (1); PETERS, MARCO (1); BROCKMANN, CARSTEN (1); MILČINSKI, GREGA (2); KOLARIČ, PRIMOŽ (2); MOČNIK, ROK (2) RIFFLER, MICHAEL (3), GIRTLER, FLORIAN (3)1: BROCKMANN CONSULT GMBH, GERMANY2: SINERGISE LABORATORY FOR GEOGRAPHICAL INFORMATION SYSTEMS, LTD.3: GEOVILLE INFORMATION SYSTEMS GMBH

http://www.s2gm.eu/


Objective of this talk

• Introduce you to the Copernicus Sentinel-2 Global Mosaic Service• Objective and scope of the service

• Algorithms used

• Available products

• Listen to the user needs• Is the service fit for purpose for REDD+?

• Where and how can S2GM improve?

http://www.s2gm.eu/


Objective and scope

• Generating composites of scientifically sound Sentinel-2 L2A surface reflectance data on global scale

• Analysis-ready data for direct and convenient usage

• Use cases include but are not limited to REDD+activities, i.e. monitoring land use and deforestation

• Expert support

• State-of-the art service provision

10m, yearly mosaic 2019 (Jan-Mid-June);Mount Kenya

http://www.s2gm.eu/


Offer and user uptake

Offer

• User-tailored mosaics and composites of Sentinel-2 L2A, best representative pixelapproach.

• European coverage (11/2016 - present), global coverage (12/2018 - present).

• Near real-time product availability, typically few days after observation.

• Free, full, and open!

User Uptake

• Rapidly growing user base with currently 893 registered users as of May 2019. 65 new users registered in April 2019 alone.

• Received 492 orders in May of which 60% have been monthly or even longer composites.

http://www.s2gm.eu/

www.s2gm.eu Copernicus Sentinel-2 Global Mosaic 10m, Quarterly mosaic 2019 Jan-Mar;Brasilia, Brazil

• Sentinel-2 Global Mosaic allows users to tailor products with respect to

• Compositing period (day, 10-day, month, quarter, year)

• Area of interest

• File format (GeoTIFF, JP2, NetCDF)

• Spatial resolution (10, 20, 60m)

• Coordinate system (WGS84, UTM)

• Bands to be included

• Auxiliary information (AOT, geometry, scene classification, etc.)

• Sentinel-2 data volumes and permutations of options make traditional approach of full-archive processing, storage, and distribution prohibitive. Instead: on-the-fly processing upon user request!

http://www.s2gm.eu/


Two Compositing Algorithms

• Short-term composite < 4 valid observations: Decision-tree approach based on spectral tests

• MEDOID ≥ 4 observations: Multidimensional median on entire spectrum

• Rigid pre-processing to eliminate invalid observations

• Generating mosaics pixel by pixel from original observations, no spectrum averaging or other image blending applied

• Spatial resampling of bands to non-native resolutions if needed

http://www.s2gm.eu/


Ordering S2GM products via Mosaic Hub

• On-request generation oftailored mosaics leveraging on cloud resources and free availability of S-2 L2A

• Mosaic Hub as interactiveuser interface

• Website and desktop application with convenient download manager

http://www.s2gm.eu/


Tailoring & Requesting

Dialogue-based Mosaic specification

http://www.s2gm.eu/


Download

• User area lists all requests

• Download manager

ensures convenient and

robust distribution

http://www.s2gm.eu/


SNAP pluginS

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http://www.s2gm.eu/


Analysis Ready products

• 3 monthly S2GM

composites

• False colour

composites using

(NIR/Red/Green) to

emphasise

vegetation change

• Simple calculation

of NDVI shows

vegetation loss

during and after the

fire

• Monitor forest fire in Bandipur, India (Wildfire outbreak 21 February 2019)

http://www.s2gm.eu/


S2GM website

Central entry point to all service components:

• Mosaic Hub

• Blog

• Documentation

• User support

• News

https://land.copernicus.eu/imagery-in-situ/global-image-mosaics/

wwww.s2gm.eu

http://www.s2gm.eu/

https://land.copernicus.eu/imagery-in-situ/global-image-mosaics/

http://www.s2gm.eu/


Documentation and support

• Algorithm Theoretical Basis Document (ATBD)

• Online User Manual

• Expert support via CLMS service desk

https://land.copernicus.eu/contact-form

http://www.s2gm.eu/

https://land.copernicus.eu/contact-form


Alternative Algorithm Development• Key characteristics of the MEDOID

• Selects the most representative pixel for a given period

• Provides a real measured spectrum

• Limitations of MEDOID algorithm for some applications• Varying per pixel cloud cover leads to difference in number of observations in adjacent pixels

• These differences lead to spatially heterogeneous pattern (salt & pepper)

• Further limitations• Sentinel-2 L2A cloud screening is insufficient

• Remaining cloud contaminations commonly lead to wrong pixel selection (especially in inner tropics)

• Goal• Reduce cloud contaminations

• Produce an additional spatially more homogeneous product (not replacing the current products, constraints regarding spatial coverage or availability may apply)

http://www.s2gm.eu/


• Simple method• 1st Input filtering using the L2A scene classification

• valid scl classes: 2, 4, 5, 6, 7 (adding cloud low prob compared to standard S2GM)

• Temporal pixel stack – annual (development version)

• Calculate visible brightness based on B2/B3/B4

• 2nd input filtering • Remove upper 45% and lower 20% percentile to remove residual clouds and cloud

shadows

• Calculate mean of remaining data

• Remark: Resulting spectra are not a genuine measurement anymore

Methodology

http://www.s2gm.eu/


Examples – Central France / annual 2018

S2GM standard product Alternative Algorithm

http://www.s2gm.eu/




http://www.s2gm.eu/




http://www.s2gm.eu/


Mosaic Hub technical details19

L2A

mosaic

definition

Step 1

UTM

MGRS

mosaic

L1

cache

Step 2

End user

mosaic

L2

cache

distribution

servicemosaic

• 2-step mosaic generator overview

http://www.s2gm.eu/


Step 1 – MGRS tile processing20

L2A

MOSAIC TILE

Mosaic engine

(STC &

MEDOID)

tile

cache

Tile

catalogue

http://www.s2gm.eu/


Step 2

• Small mosaics (< 10.000px x 10.000 px)• Reprojection

• Crop to AOI

• Stitch

• Convert to proper output format

• Generate metadata in proper format

• Large mosaics• Crop to AOI

• Convert to proper output format

• Generate metadata in proper format

21

http://www.s2gm.eu/


System and it’s benefits

Processing system• Queuing – 3 tiles per order then switching to next order

• 200 virtual machines

• on average 15 minutes per tile

Benefits of on-the-fly processing• better management of resources

• flexibility• algorithm improvements, bugs• new features

22

http://www.s2gm.eu/


Consortium

• Three European SMEs with complementary expertise in Earth Observationsince many years.

• Clearly defined roles in S2GM service

• Managing contract and consortium

• Mosaicking algorithms• Sentinel-2 (pre-) processing

expertise

• Maintaining S2 L2A archive• Mosaic Hub technology• Distribution of products

• Internal quality control• Thematic expertise land

http://www.s2gm.eu/


Summary

Copernicus Sentinel-2 Global Mosaic service

• provides scientifically sound mosaics of Sentinel-2 surface reflectance data on a global scale

• is fit for various applications

• is free to use by everyone

• is accessible via www.s2gm.eu and via CLMS

• is operated by a team of dedicated experts ready to support users

http://www.s2gm.eu/

http://www.s2gm.eu/


Thank you for your attention!Questions for discussion:

• What evolution of products could optimally support REDD+?

• Which service functionalities are of highest priority?

http://www.s2gm.eu/


Contact [email protected] the Service desk of CLMS at

www.s2gm.eu for more information!

http://www.s2gm.eu/

mailto:[email protected]

http://www.s2gm.eu/

Documents

Copernicus Sentinel-2 Global Mosaic