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Architecture of a Satellite-
Based Sensor Network
for Environmental
Observation
Wei Ye, Fabio Silva, AnnetteDeSchon and Spundun Bhatt
Project funded by the Advanced Information Systems Technology (AIST) program
NASA Earth Science Technology Conference (ESTC), June 25, 2008
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Introduction
Sensor webs enable on demand, adaptive sensing across a
wide range of spatial and temporal scales from both in-situ
and space-based sensors
Broad vision: enable wide adoption of sensor web technology
in scientific research
In-situ sensing networks are important components of large-
scale sensor webs (focus of this paper)
Explore opportunities of combined in-situ sensing and space-
based sensing (future direction)
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Challenges in Building Sensor Nets for Science
Rapidly deployable in remote locations by individual scientists
Flexible to support different science applications
Robust to harsh environments and potential failures
Intuitive user interfaces and tools for scientists
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Our Approaches
Develop a turn-key system that addresses above challenges,
called Sensor Processing and Acquisition Network (SPAN)
• Emphasize on modular and extensible design
How to address those challenges?
• Remote locations: use satellite communication (or cellular)
• Different science apps: develop a unified sensor integration framework
• Robust operation: extensive system monitoring and failure recovery
• User support: intuitive interfaces and tools to monitor and reconfigure the
system
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Outline
Introduction
System architecture
Prototype implementation
Lessons learned from initial deployment
Conclusions
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High-Level SPAN Architecture
Internet
ScientistIn-situ sensor
networks
Satellite
communication
Data acquisition, meta-data tagging,
reliable transmission, WAN access
SSG Front End
(deployed in field)
Data storage, user interface
SSG Back End
(deployed in lab)
SSG Front End
Space-based
sensors
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Major Functions in SPAN
Analog &
digital
instruments
for earth
science
A-D,
calibration,
scheduling,
metadata
tagging
Robust
data
txfer
WAN
access
terminal
Internet
access
Local
wireless
Data &
metadata
staging &
storage
Visualization
& analysis;
system
management
SPAN front end SPAN back end
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SPAN Front End (in the Field)
Sensor Management
Data Acquisition
Data and metadata management
Reliable data transmission
WAN access
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Unified Sensor Integration Framework
Framework for easy sensor integration
• Simple, low-level hardware to interface with various sensors
• Modularized and extensible driver library
Analog sensors
Digital sensors
Serial sensors
Networked sensors
FPGA
interface
Serial
interface
Network
interface
Sensor
driver
libraryLow-level
driver
Low-level
driver
Common
API
Hardware Software
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Sensor Driver Library
Streamlined sensor integration
• Mapping different sensors into system
• Support analog, digital, serial, networked sensors
Software abstraction to easily control sensors
• Unified API to control different sensors
– Enable or disable channels, set sampling rate, raw data or average
• Obtain metadata for each channel
– Sensor make, model, serial number, measurement type and unit, etc.
• Sensor calibration
Modular and reusable software components
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Protocols for Data and System Management
Designed protocols for managing data, control and status information
Implemented protocols on CompactRIO
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SPAN Back End (in the Lab)
Data storage
• Support both databases for individual scientists or shared by community
Provide three types of user interfaces
• Command interface: control and reconfigure system remotely
– Start or stop a sensor, or change sampling rates
• Data interface: easily access sensor data and metadata
• Status interface: monitoring status of entire system
– Component failure, availability of satellite link
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Provide Different Methods to Access Sensor Data
Different access methods meet different needs
SPAN
system
Live data feed
real-time, no reliability
guarantee
Database storage
reliability guarantee even
when components fail
Private use
MySQL database
Publish and
sharing
SensorBase
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Outline
Introduction
System architecture
Prototype implementation
Lessons learned from initial deployment
Conclusions
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Platform Consideration
Data acquisition system: CompactRIO
• Rugged platform, rich sensor interfaces, LabView programming
Communication technologies
• WAN: WildBlue satellite-based Internet service
• Local wireless: mote-based wireless sensor network
Embedded PC: Stargate
• Drives satellite modem and provides access control
Database: MySQL database
• Robust open-source database on Linux
Network monitoring tools: Nagios
• Nice graphical interface
CompactRIO
Stargate
Mica2 mote
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System Integration
Hobo data logger
Mote
Front End
Back End
To satellite
CompactRIO
Sensors Stargate
Sensors
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Block Diagram of the Integrated System
Major system components
• CompacRIO: connects to
wired environmental sensors
• Stargate (Linux PC): provides
access control and connects
to wireless sensors
• Data grabber: reliable data
retrieval from front end and
injection into database
• SensorBase: Database for
scientists
• Nagios: system monitoring
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Outline
Introduction
System architecture
Prototype implementation
Lessons learned from initial deployment
Conclusions
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Scientific Application at Stunt Ranch
Ecological research
• Investigate the influence of
southern California drought
conditions on different
species of plants
• Use constant-heating sap
flow sensors to monitor the
flow of water through the
xylem of replicated stems of
plants
• Scientist: Prof. Phil Rundel at
UCLA
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Front-End System
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Deployment at Stunt Ranch
Complete front-end sysem
• CompactRIO
• Stargate
• Environmental sensors
– Solar radiation (PAR)
– Precipitation
– Wind speed
– Temperature
– Humidity
WildBlue satellite comm
Sap flow sensors on selected
plants
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Initial Sensor Data Collection
Provided sensor
data to scientists
System operates
reliably during first
three months
• No system crash
• No data loss
• Discovered and fixed
a few bugs for
second round of
deployment
Correlated sensor
data from
precipitation, relative
humidity and solar
radiation
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Real-Time Data Access
Real-time data access in
SensorBase
• Provide real-time to
scientists with database
access
• Can be shared among
different scientists
Easy access with
web interface
Cleanly organized
sensor data
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Other Lessons Learned
Even the site has line power, cannot assume it is reliable
• We saw several instances that the power was cut due to unknown reasons
• Needs backup battery to report emergency events
Protect the equipment from honeybees (and other insects)
• We found a honeybee hive with hundreds of bees inside our equipment box
after a few months of deployment
• Needs better sealing
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Conclusion
Sensor webs can be a powerful technology for environmental
and ecological research
• Combine in-situ and space-based sensor systems
• Dynamic reconfiguration
Our current focus is developing robust and easy-to-use in-situ
sensor networks
The architecture of our system has been validated with our
first prototype deployment for ecological research
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Future Directions
Standard-based data management
• Had good discussion with Mike Botts on SensorML at Sensor Web PI meeting
Automated and distributed system reconfiguration
• Fast response to triggering events
Explore systems and applications that combine in-situ sensing with
space-based remote sensing
• We are interested to find collaborators
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Thank you! Questions?
Project is funded by NASA ESTO’s AIST program as “Satellite
Sensornet Gateway (SSG)”
• website: http://ssg.isi.edu