The Satellite Sensornet Gateway (SSG) is a building block intended to encourage the deployment and operation of in-situ sensornets and promote Earth science research, specifically by enabling creation of datasets taken from webs of in-situ sensors in remote locations within North America and around the world. The SSG connects local sensornets — which may be broadband, wireless, and populated by many sensors — with satellite networks which, through their long reach, allow data archiving, management, and commanding at a network operations center convenient to the scientist. The SSG is the center around which the sensornet is built: it controls and commands the sensornet and it collects and pre-processes data.

SSG Components

Sensors

Provided by the investigator.  Sensors come in three basic varieties: analog, simple digital, and sophisticated digital.  Analog sensors generate a variable voltage, current, or resistance and may require power for stimulation.  Simple digital sensors generate measurements sent serially using a protocol such as RS-232 or SDI-12.  Measurements may be generated periodically or in response to a query via the same interface.  Sophisticated digital sensors may include full data-loggers and or microprocessors.  They may have serial or network interfaces and rich command sets.

Data Acquisition System

We are developing a data acquisition system based on the NEON Wireless Platform. (web)   The technology we chose is the National Instruments' CompactRIO system (web).  We are developing a general purpose data acquisition, commanding, and transmission application for this platform using the LabView development environment.  Our objective is that the system would not need additional LabView programming by users, requiring only minimal configuration to integrate a wide range of sensors and network technologies.

Local Wireless Connectivity

Many WAN technologies, satellite in particular, have sufficiently high power requirements to motivate locating the WAN terminal near line power.  In order to free the user from having to locate the sensors in the same place, we include local wireless.  Our current baseline is 900MHz system with a range of 40 miles (assuming clear line-of-sight) and improved foliage penetration compared to 802.11.

Delay-Tolerant Networking (DTN)

Wireless technologies, satellite and terrestrial, may interact poorly with network protocols such as TCP.  The long delays associated with link-layer retransmission or satellite propagation may also result in data loss should a system component fail.  Delay-Tolerant Networking (web) is the result of a research project looking at improving network capabilities in the face of networks which include very long delays or disconnection.  We plan to use DTN software between the data acquisition system and the user archive.

WAN Access

The system will support a wide range of WAN access technologies.  Principal among them is satellite-based Internet access and our initial development will integrate a service such as WildBlue (web).  However, other technologies such as cellular GPRS, packet radio, or line-of-site microwave may have preferable cost and/or performance under certain circumstances.

Network Monitoring System

To avoid data loss, users need to understand the state of the end-to-end system.   SSG will include an open-source network monitoring system that the user can run permitting easily verify end-to-end reachability and liveness of key components. 

User Data Archive

Measurement data and system context (i.e., metadata) must be stored in a manner usable to scientists.  It is not our intention to proscribe how a scientist should use collected data.  Instead, we intend to collect the data into a database which is adaptively structured based on the array of instruments deployed in the field.  Additionally, we are investigating other work in this area to include other technologies which are useful, current, and stable.