## 1 Introduction  
Wireless sensor networks are changing our way of life just as the Internet has revolutionized the way people communicate with each other. Wireless sensor networks combine distributed sensing, computation and wireless communication. This new technology expands our sensing capabilities by connecting the physical world to the communication networks and enables a broad range of applications. Observing microclimate changes is one of the most popular applications of wireless sensor networks [1]. Sensor nodes can be deeply embedded and densely deployed to enable up-close monitoring of various indoor or outdoor environments. However, some environments are often too dangerous or inaccessible to humans. For example, a building on fire or a suspected hazardous material leak. Although monitoring of sensitive wildlife and habitats has few potential hazards, the intrusion of humans is always a bothersome problem. Some environments cannot be accessed by humans or large robots because of terrain and space limitations. In all these situations, wireless sensor network users will face many challenges, such as deployment, network maintenance and repair.  
In recent years, the interaction of distributed robotics and wireless sensor networks has led to the creation of mobile sensor networks. It is considered that augmenting static sensor networks with mobile nodes can solve many of the research challenges that exist in static sensor networks [2]. A mobile sensor network is composed of a distributed collection of enhanced nodes. Each node has sensing, computation, communication and locomotion modules. Compared to the conventional static wireless sensor networks, mobile sensor networks have more powerful network capabilities such as self-deployment, network repair and event tracking. Each mobile senor node is capable of navigating autonomously or under control of humans. Large numbers of mobile sensor nodes can coordinate their actions through ad-hoc communication networks.  
Some research groups have begun to design mobile nodes for wireless senor networks and have made some prototypes. In [3], The Robomote is introduced as a tabletop platform for experiments on mobile sensor networks. It is more than 1,300 times smaller than Pioneer robots which are commonly used in laboratories across the world. CotsBots is another modular robot platform for research in distributed robotics [4]. It is built entirely from off-the-shelf components and requires minimal assembly. Some additional sensor modules need to be added to the CotsBots platform in order to get better performance in a sensor network environment. Other similar platforms such as Millibots, MICAbot and Racemote also have met the concept of mobile sensing [5-9].  
Although the existing platforms have provided initial support for developing large-scale mobile sensor networks and distributed robotics, their controllability still needs improvement. How to build models for mobility and networking management and how to interact with these special networked systems still need to be further investigated. This paper presents a mobile sensor network system for monitoring of unfriendly environments. The system architecture, the mobile node design, the basic behaviors and advanced network capabilities have been investigated respectively. Details of this work will be presented in Section 2-4.