Impact of Drifter Deployment on the Quality of Ocean Sensing

Traditional means of observing the ocean, like fixed moorings and radar systems, are expensive to deploy and provide coarse-grained data measurements of ocean currents and waves. In this paper, we explore the use of an inexpensive wireless mobile ocean sensor network as an alternative flexible infrastructure for fine-grained ocean monitoring. Surface drifters are designed specifically to move passively with the flow of water on the ocean surface and they are able to acquire sensor readings and GPS-generated positions at regular intervals. We view the fleet of drifters as a wireless ad-hoc sensor network with two types of nodes: i) a few powerful drifters with satellite connectivity, acting as mobile basestations, and ii) a large number of low-power drifters with short-range acoustic or radio connectivity. We study connectivity and uniformity properties of the ad-hoc mobile sensor network. We investigate the effect of deployment strategy. The objective of this paper is to address the following challenge: how can we trade the usage of resources (e.g. number of drifters, and number of basestations vs. communication range) and which deployment strategy should be chosen (e.g. grid-like, star-like, etc.) to minimize energy costs, whilst satisfying application requirements for network connectivity and sensing density. Using simulation and real dataset, we investigate the effects of deploying drifters with regard to the following questions: i) where/when should drifters be placed initially? ii) how many drifters should initially be deployed?, iii) the effect of the number of basestations (drifters with satellite connectivity) on the overall network connectivity, and iv) the optimal communication range of the basic drifters. Our empirical study provides useful insights on how to design distributed routing and in-network processing algorithms tailored for ocean-monitoring sensor networks.