This document summarizes the technical aspects of the third Secure Societies pilot project. The pilot uses multiple data sources including satellite imagery, news articles, and Twitter posts. It has two main workflows: a change detection workflow that analyzes satellite images to detect changes over time using image processing techniques, and an event detection workflow that monitors social media and news to cluster events. Both workflows store results as linked geospatial data for visualization and querying through an interface. The change detector component parallelizes change detection algorithms on images using Spark.

1. 5th BDE Hang-out “Big Data in Secure Societies”
Giorgos Argyriou, University of Athens
Researcher
13/12/2017
TECHNICAL ASPECTS OF THE 3RD
SECURE SOCIETIES PILOT

2. Image
Aggregator
Change
Detector
GeoTriples
News
Crawler
…
Strabon
storage
User
Interface
Event
Detector
Lookup
Service
Keyword
Search
Cyber-
security
Event Detection Workflow
Change Detection Workflow
Entity
Extractor

3. Pilot Data Sources
◎ Sentinel-1
o Satellites operated by ESA in the framework of the Copernicus programme funded and
managed by EC. (free and open data)
o Same area acquired every 6 days with 2 satellites
o Sentinel-2
o Multispectral images (free and open data)
◎ Reuters
o News articles through RSS feeds in XML format
◎ Twitter
o Free Twitter Public Streaming API and specific user accounts
o Plain text along with metadata in JSON format
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4. Pilot Details
◎ Change Detection Workflow
o System able to search, download and process images in parallel (Spark)
o Operators from SNAP: Read, Subset, Calibration, Create Stack, GCP, Warp, Change
Detection, Write
o Operators implemented: DB Scan, Terrain Correction
◎ Event Detection Workflow
o System able to periodically monitor social media and news agencies
o Events are identified as document clusters (Spark)
o Events mapped to geolocations (Lucene)
◎ Common workflow
o GIS interface (Sextant) allows users to activate the two workflows
o Geographic information stored in RDF store Strabon and queried through stSPARQL
o Linked geospatial data as the integration technology (Strabon, SemaGrow and Sextant)
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5. Change Detection workflow
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User
Interface
Image
Aggregator
query
query downloading
images storing
images
read
images for
processing
Image processing initiation storing results
storing results
as RDF
Change
Detector
Return results for visualization
GeoTriples
Strabon

6. Change Detector
 Parallelizes the change detection algorithm using Spark.
 Input: Two satellite images depicting the same geolocation.
 Output: A set of the areas with differences between the two images.
 Preprocessing to align the given images
 Preprocessing to align the given images: Subset Operator
 Main processing: Calibration, CreateStack, GCP, Warp, Change Detection
 DB Scan for clustering together pixels with changes
 Sentinel 2 images quick-looks
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Terrain Correction

7. Using the Pilot
 Video of the pilot. A user requests Change
Detection
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8. Thank you!
Links
 Sextant: http://sextant.di.uoa.gr/
 Strabon: http://strabon.di.uoa.gr/
 GeoTriples: http://geotriples.di.uoa.gr/
More details about the SC7Pilot: http://pyravlos-vm5.di.uoa.gr/bde-website/
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