CHEMICAL SENSOR SELECTION AND OPERATION GUIDE 299 that operate at room temperature and devices that behave as "self-diagnostic arrays." Advances in the basic understanding of sensor mechanisms will come from systematic study of effects of variations in oxide composition, from studies of surface modification and its consequences, and from application of new tools of computational chemistry. 7. Development of autonomous sensor systems. At present the research in this field typically progresses from bench-top prototypes to study systems operated in situ and finally to production of opera- tional systems that are accessible to the broad community. The use of wireless systems implies more convenience and leads to a considerable cost reduction. An advantage of wireless sensor systems is that they can be placed without restriction, and can therefore record the measured quantity close to its occurrence and independent of potential harsh circumstances. Energy-autonomous sensors will gain particular importance among wireless sensors (Tränkler and Kanoun 2001), because in this case no wires are necessary, even for electricity supply. Johnson (2003) believes that autono- mous observing systems using chemical sensors are becoming well poised for use in the next generation of global atmospheric and biogeochemical studies. Autonomous in situ systems can provide effi cient monitoring of temporal changes on scales that are cost-prohibitive using ship- board measurements. Mobile platforms, such as gliders, floats, drifters, and volunteer observing ships (VOS) will give sensor systems access to broad geographic regions. In addition to acquiring data at improved spatial and temporal scales, in situ analysis can potentially improve data quality by minimizing sample contamination as well as transformations of meta-stable seawater and at-