SENSOR NETWORKS: ENVIRONMENT MONITORING

In this post, let us take an example where sensor networks are deployed to study the environment.  When sensor networks were not around, the environmental scientists had to go deep in the field (you’d have probably seen on Discovery or National Geographic) and face the harsh conditions each time they find the need to record new observations.  But, with WSN the scientists can not only gather data frequently but also with much leisured ease.

For instance, monitoring the microclimate throughout the volume of redwood trees, helps form a sample of entire forests. Redwood trees are so large that the entire ecosystem exists within their physical envelope. Climatic factors determine the rate of photosynthesis, water and nutrient transport, and growth patterns. Substantial variations are known to exist over the volume of an individual specimen, and researchers believe that the microclimatic structure varies over regions of the forest. In addition, water transport rates and the scale of respiration may influence the microclimate around a tree, effectively creating its own weather. These factors greatly influence the habitat of the species existing in and on the trees.

Earlier, the scientists used a winch to reach the top portions of these trees and record their measurements manually. But, these results were not conclusive because of the fact that their measurements would be at a particular time of the day and using just one sample of the reading it is indeed hard to judge how the climate would be progressing throughout that particular day.

Following is the figure of a node in WSN used for environment monitoring.  

An entire weather station is of the size of a film canister. Two light sensors at the top measure the total solar radiation, especially the photosynthetic radiation bands at which chlorophyll is sensitive. There are also sensors at the bottom which measure the temperature, relative humidity and barometric pressure. These nodes are kept in the shade which protects them from rain.

The weather protected node also houses a computing device, battery, a miniature transceiver to collect data, process it and route the information through other nodes to the outside world. Using these sensor nodes is far more effective to collect data across different elevations of the tree for prolonged period of time.

Following is the the temperature profile over three days, collected from 16 nodes at four elevations in a 35-meter study tree. The WSN samples climate data every five minutes and computes an average temperature at each elevation. The measurements show that within the expected daily cycle, the top of the tree experiences much wider climatic variation than the forest floor.

The network data also illustrates the progression of temperature wave-fronts in a single day. It also gives pertinent information about the relative humidity. It has been found that redwood trees move huge volumes of water in a single day creating powerful temperature and humidity gradients that could be instrumental in understanding the growth dynamics, nutrient transport and water intake of such large structures thereby iterating the dense instrumentation.

Initially, researchers can intensively study the environment by analyzing the results. In the future, they can reprogram the WSN remotely to monitor information pertaining to deviation from regular climatic data. This would increase the lifetime of the WSN significantly.