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Next-Generation Oceanographic Sensors for Short-Term Prediction/Verification of In-water Optical Conditions

Mark L. Wells*


Assessment and prediction of in-water optical conditions for coastal waters and inshore seas remains an important but elusive goal for ONR, NSF and NASA research. Layered upon small scale spatial variability in optical characteristics in coastal regions is the temporally dynamic coupling among physical, chemical and biological parameters that regulate ocean optics. Predictive models built upon our incomplete understanding of these linkages provide general hindcast capability for environmental conditions, but prove to be largely unreliable for accurate forecasting in these dynamic environments due to insufficient data streams of critical parameters. Improving forecasting accuracy will require information based on widely distributed, sensor-based observing systems capable of measuring multiple parameters simultaneously at high temporal and spatial resolution. Implementation of these sensor networks, particularly beyond the narrowly focused physical infrastructures of ocean observatories, awaits the development of next-generation oceanographic sensors.

Environmental sensors can be broadly categorized as measuring physical, chemical, or biological properties. Of these, physical sensor technology is the most mature, with well-established field-deployable sensors for a number of basic oceanographic parameters (e.g., temperature, pressure, salinity, light, turbidity). In contrast, there exist only limited capabilities for field-deployable chemical sensors (e.g., dissolved oxygen, pH, redox state) and there are essentially no specific biological

*

School of Marine Sciences, University of Maine



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OCR for page 135
Next-Generation Oceanographic Sensors for Short-Term Prediction/Verification of In-water Optical Conditions Mark L. Wells* Assessment and prediction of in-water optical conditions for coastal waters and inshore seas remains an important but elusive goal for ONR, NSF and NASA research. Layered upon small scale spatial variability in optical characteristics in coastal regions is the temporally dynamic cou- pling among physical, chemical and biological parameters that regulate ocean optics. Predictive models built upon our incomplete understanding of these linkages provide general hindcast capability for environmental conditions, but prove to be largely unreliable for accurate forecasting in these dynamic environments due to insufficient data streams of criti- cal parameters. Improving forecasting accuracy will require information based on widely distributed, sensor-based observing systems capable of measuring multiple parameters simultaneously at high temporal and spatial resolution. Implementation of these sensor networks, particularly beyond the narrowly focused physical infrastructures of ocean observato- ries, awaits the development of next-generation oceanographic sensors. Environmental sensors can be broadly categorized as measuring physical, chemical, or biological properties. Of these, physical sensor technology is the most mature, with well-established field-deployable sensors for a number of basic oceanographic parameters (e.g., tempera- ture, pressure, salinity, light, turbidity). In contrast, there exist only lim- ited capabilities for field-deployable chemical sensors (e.g., dissolved oxygen, pH, redox state) and there are essentially no specific biological * School of Marine Sciences, University of Maine 135

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13 OCEANOGRAPHY IN 2025 sensors (other than chlorophyll fluorescence) to provide key information on the production, structure, and composition of biologically influenced ecosystems in real time. Though much insight can be inferred from the current spectrum of sensor capabilities, accurate assessment of the broader chemical and biological parameters will be essential for accurate forecasting of in-water optical conditions. Moreover, none of the current sensor technologies provide logistically feasible capabilities for generat- ing in-water, real time, high-density spatial and temporal data streams from remote coastal regions. Fundamental to meeting these needs are the requirements that future sensors be robust, require low power, have fast response, require no main- tenance (e.g., disposable), are adaptive (meaning that they can alter sam- pling strategy based on power needs, detection of an ‘event’, etc.), and, perhaps most importantly, that they comprise small, inexpensive units. For example, were the physical dimensions of current sensor packages to fall by three orders of magnitude, one could readily envision deploy- ment of disposable adaptive sensor “swarms” by ocean currents, air, or other means that would report back real time data on the ocean field. While some opportunities certainly exist for sensing improvement by linking novel current capabilities, entirely new technological approaches will be crucial to significantly advance sensor capabilities. It is necessary that oceanographers begin to think differently about sensor research and development. Nanotechnology arguably offers the most promising venue for achieving new advances in sensor development. Nanotechnology is a highly interdisciplinary science and engineering field that explores and exploits the unique phenomena occurring at the atomic, molecular and supramolecular scales to create materials, devices and systems with unique properties and functions. There are both “bottom-up” processes (such as self-assembly) that create nanoscale materials from atoms and molecules, as well as “top-down” processes (such as milling) that create nanoscale materials from their macro-scale counterparts. Nanoscience and nanoengineering offer a unique, largely untapped resource for new sensing modes that take advantage of unique interfacial energy proper- ties, communication schemes, and even energy scavenging approaches to power longer-term sensor operations at the nanoscale. The unique properties of nanomaterials give them novel electrical, catalytic, mag- netic, mechanical, thermal, or imaging features that are highly desirable for applications in commercial, medical, military, and environmental sec- tors. There exist current application examples of extreme miniaturization prototypes of complex systems (e.g., a rice-sized gas chromatograph, a microscopic and motile wireless oxygen sensor), and industrial advances in nanofabrication currently enable the high-volume production essential

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13 MARK L. WELLS to support the enormous spatial sampling demands for integrative sen- sor capabilities. Moreover, nanotechnology offers a unique foundation for transformative science and engineering strategies of sensor design to attain the chemical and biological resolution needed to understand and predict the coupling of biology and ocean optics. But a substantial new intellectual investment towards developing next-generation sensors will be essential to achieve this objective. The observation that developing nanotechnologies hold enormous potential for sensors has been noted in numerous previous workshops and study reports. However, nanoscience so far is largely unrealized as a foundation for environmental sensors, particularly field-deployable sen- sors. The central roadblock is that the nanoscience and nanoengineering expertise and research-supporting infrastructure is largely unknown and inaccessible to most oceanographers. There is a need to bring a differ- ent set of players to the table; representatives of potentially synergistic fields that would not otherwise cross paths. Herein lay a major stumbling block. Fundamental differences in research culture, knowledge base, and funding source and expectations create a barrier between oceanogra- phers and nanoscience and nanoengineering. NSF currently is being lob- bied to develop a new initiative in Geosciences to help break down the boundaries between science and engineering in the research community. The intent of this initiative would be to enable and promote a strong collaborative atmosphere between geoscience and nanoscience engineer- ing for developing novel and transformative field-deployable sensors to empower existing and future global observing networks. Establishing a broad cross-agency support for this new collaboration would enable sub- stantial advances in next-generation sensor capabilities by 2025. To summarize, the challenge of populating current and future envi- ronmental observing networks with relevant sensing capabilities will not be met using current technology. Nanotechnology provides a major, largely untapped avenue for the transformative research and engineering needed to attain full utilization of these global observation networks, but oceanography lacks a critical mass of researchers who bridge with nano- science, nanoengineering and industry. This situation will not change substantially without specific steps to lower the barrier between these dis- tant research spheres, while also incorporating the industrial participation essential to linking sensor research to commercially available products.