Motivation
LUSTER, a joint project between LTER ecologists and EWSNs Engineers, aims to address research challenges from both sides
Ecological Motivation
Shrub cover is increasing worldwide, most often by replacing herbaceous-dominated communities, especially grasslands. In North America, this phenomenon has been documented in a range of environments from desert grasslands and arctic tundra to Atlantic coast barrier islands. Shrub encroachment has been linked to climate change and anthropogenic factors; however, the causes have not been thoroughly investigated. Perhaps most dramatic is the change in the light environment as community structure shifts from grassland to shrubland.
Little information is available on the link between shoot architecture and light absorption characteristics of dominant canopy trees, much less for shrubs. Additionally, most studies measure light either at a single point in time or over periods of minutes or hours. However, there is a need to quantify light at finer temporal scales because photosynthetic responses occur within seconds and courser measurements often underestimate the effects of brief, but intense, direct light. Measuring light at a fine spatial and temporal granularity is the primary purpose of the LUSTER system.
Scientists hypothesize that a high leaf area index (LAI) and the dense and even display of leaves on shrubs reduce the number and size of gaps in the canopy. These changes create a more spatially homogenous light environment, reducing the occurrence of microsites with a favorable light regime for grasses and other plants.
In moist systems, where transpiration demands of a dense leaf canopy can be supported, the influence of shrubs on the light environment should be pronounced. As precipitation decreases in arid environments, LAI should decline due to the relatively high evaporative demand and light should be less of a limiting factor beneath shrubs. However, only a small increase in LAI may be sufficient to reduce grass density because of a low shade tolerance of species common to grasslands. Future management plans for shrublands and grasslands depend on the ability to predict the impacts of shrub encroachment and will require knowledge of the interactions between shrublands and adjacent grasslands, especially where shrubs are expanding.
Motivation for Environmental WSNs
Wireless sensor networks for ecological research often have to be deployed in harsh environments where they need to survive the elements of nature and function for extended periods of time with no further access for several months. Imagine a monitoring system deployed in polar regions where access is available only during certain months of the year. The system must keep functioning even when parts of it fail due to environmental or other reasons. The need for such a reliable, fault-tolerant system is the main motivation for the design of LUSTER. Our system is designed to address the following challenges:
- Fast deployment time Deploying large numbers of sensor nodes in itself is very time consuming. A self-organizing system is needed to free users from the extensive setup tasks.
- Deployment assurance At deployment-time, deployers have to ensure that the system will continue to run without expensive and time consuming return visits to the site. connection.
- Reliable and trustful data service The system must provide reliable and trustful sensor readings with potential sensor malfuction, node failure and loss communication links
- Online data access The system should provides access to the real time sensor readings as well as to the history data at several levels: the database and web server on the Internet and the distributed storage on the WSN.
- Heterogeneity in sensors and hardware System architecture and query system may include many types of sensors. The query system supports any direct sample and split-phase sensors. An extensible API allows driver development for custom sensors where special handling of hardware or processing are required.
- Environmental challenges rain and humidity are mostly tolerated through sealed packaging and dessicant inserts. However, some challenges are most unexpected. For example, we learned that one of the hazards for equipment left on the islands of the Eastern Shore of Virginia is that exposed cables are subject to the teeth of small critters.