rapid detection of rare geospatial events: earthquake warning applications a review by zahid mian...
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Rapid Detection of Rare Geospatial Events:
Earthquake Warning ApplicationsA Review by Zahid Mian
WPI CS525DSeptember 10, 2012
ARE INEXPENSIVE SENSORS CAPABLE OF DETECTING SEISMIC EVENTS? Cheap Sensors (16-bit MEMS accelerometer) Cell Phones (Android) Distributed Event Based (DEB) Community-Wide Participation Cloud Computing
Problem/Goal
Most Cells Phones Today Have Accelerometers (used to obtain seismic measurements)
Cell Service Increasing Around the World, Even in Impoverished Regions like Haiti
Cost of Such Devices Decreasing The Denser the Network of “Sensors”, the
More Accurate the Results
Why Cell Phones?
Sending Messages (“picks”); Limitations 16-bit MEMS accelerometer
Relatively Inexpensive More Accurate (than phones) Stationary
Cell Phones (Android) “No” Expense (practically) Less Accurate (someone can drop a phone) Truly Mobile
Sensors
Increased Number of Sensors Makes it Easier to Visual the Propagation Path of an Earthquake
Why Use Many Sensors (“Dense Network”)
Google App Engine Many Benefits of PaaS; Scalable, Distributed, etc.
Handles Registration of Sensors Handles Messages Checks Heartbeat Datastore Computational Analysis Detection
Cloud Based Infrastructure
Overview of CSN Architecture
Synchronization: Use Entity Groups & Task Queue Jobs
Timeframe Limitation: no single points of failure & tolerant of data loss
Query Limitation: Numeric Geocells
Limitations of App Engine
How to Store Latitude and Longitude Pairs AND Create Flexible Query? Solution: Create a Binary String to encode
Information What does “011011” mean?
Defines Location and Resolution
Encoding Geospatial Data
Encoding a Geocell
00 10
1101
Encoding Rule:If point lies east of mean longitude,
set longitude bit to 1If point lies north of mean latitude,
set latitude bit to 1
Example: 43.14 N, 118.12 W
01 10 01 10 01
STA/LTA (Short Term Average over Long Term Average) “Pick” when ration reaches above a threshold
Anomaly Detection using Density Estimation (ADDE) Use sensory data to determine anomalies Several factors need to be considered Ultimately used to determine false positives
and the number of messages to send
Sensor-side Picking Algorithms
STA/LTA vs. ADDE
Detection Algorithm must be Insensitive to the reording of messages Insensitive to the loss of small number of
messages Solution: Use 2-Second Buckets When Geocell Activated, a Task Queue job
performs further Analysis
Server-side Pick Aggregation
Geocell Detection Performance
Simulation: Geocell-based Regional Event Association
Simulation: Naive Event Association
Acceptable for Determining Lower Bound
Quake Catcher Network (QCN) USB sensors attached to laptops No Cloud Computing
NetQuakes expensive stand-alone seismographs
Related Work (Seismic Networks)
Traffic Monitoring Environmental Monitoring Use Sensors to Capture Data, But Not Predict
Rare Events
Community and Participatory Sensing
Cell Phone Service May Not Work When Needed Too much “Noise”
May Generate False Alerts Earthquake Detection is “Difficult”
Many theories over the years and many false claims Collecting Data Via Sensors is Useful
Can Lead to Better Modeling for Future Can Validate Certain Claims
Infrastructure Can be Used for Something Else
Conclusion