Next Generation Environmental Monitoring Using Large Ensembles of Micro- and Nanotechnology-Enabled Airborne Probes

This paper will present results from a recently awarded National Science Foundation Small Business Innovative Research (SBIR) grant to design and develop a new observing system that features an ensemble of disposable, airborne probes that will make measurements as they drift passively through the air with no active propulsion or flight. The probes will exploit miniaturization as well as integration of such as micro sensors, power sources, and other micro-/nanotechnology-based components to minimize complexity, cost, size (2 to 3 cm), mass (< 1 gram), terminal velocity, and power consumption yet still provide accurate measurements compared with currently accepted observing technology. Most efforts to reduce the size and cost of in situ atmospheric instruments have not realized the full benefit of electronic component miniaturization and integration due to design constraints and functional specifications.

The probe innovation is based on more than a decade-long trend for ubiquitous sensing and “smart dust” – extremely large numbers of disposable, low cost electronic devices that measure various parameters and communicate that data to support many applications. The original vision for the smart dust initiatives was to build self-contained, millimeter-scale computing, sensing, and communication platforms to enable integrated, massively distributed, ad hoc networks. The probe design will leverage the research and development on sensor-driven microsystems by academia, government laboratories, and industries to achieve the vision for ubiquitous sensing of the atmosphere.

The probe will include micro sensors to measure ambient air temperature, relative humidity, and pressure. Air velocity will be determined based on probe position changes similar to weather balloons. Communication with each probe will be accomplished using far-field, radar responsive radio frequency identification (RFID) technology already developed for military applications involving tagging, tracking, and location. With semi-active, radar-responsive RFID tags onboard the probes, interrogators could be airborne or ground-based Doppler radars. Probes could be deployed in several ways including from aircraft or as payloads on weather balloons which leverages existing infrastructure and provides a means to release them at different altitudes. Releasing a cluster of probes provides significant redundancy in the event of a single probe component malfunction or failure.

The initial application is improving short-range (< 24 hour) weather analysis and forecasting by greatly expanding the time and space density of temperature, pressure, wind velocity, and humidity measurements throughout as much of the relevant atmospheric volume as possible. Such data could provide calibration and validation for space-based remote sensing of tropospheric winds and carbon dioxide or other trace gases as long as the probe design can integrate sensors with the appropriate form factor and power requirements. This capability could extend the potential of the system for applications involving air quality and greenhouse gases initiatives relating to global climate change.

This new observing system offers a unique approach to fill data gaps with in situ measurements over data sparse regions and improve short-range forecast accuracy well beyond current capability. These measurements would be ideal for a multitude of targeted observational campaigns as part of research and operational missions (e.g. hurricane reconnaissance) where it is only economical at the present time to obtain high-resolution spatial and temporal resolution in situ measurements over limited domains.

For the hurricane problem, there have been substantial improvements made in hurricane track forecasts with errors decreasing steadily during the past decade. However, similar trends in intensity forecasts are not evident and there is substantially less skill in predicting the formation, intensification, fluctuation, and decay of such storms. Recent work suggests that part of the problem is due to the lack of routine, four-dimensional observations with sufficient spatial and temporal resolution to initialize hurricane structure and intensity in numerical weather prediction (NWP) models.

Given that the National Oceanic and Atmospheric Administration routinely flies operational and research aircraft reconnaissance missions into Atlantic hurricanes, there are significant opportunities to provide ultra-high spatial and temporal resolution measurements for this application. The number of probes released for any given mission is envisioned to be at least two orders of magnitude larger than what is practical with current in situ instrumentation such as dropsondes considering the differences in size, mass, and terminal velocity. Such data could lead to a more thorough understanding of processes involved in vortex dynamics and physics, improved representation of such processes in NWP models, and ultimately greater accuracy in forecasts. The economic and social value of improved tropical cyclone forecasts is directly linked with saving lives and avoiding over-warning of regions. For example, small improvements in forecasts of land falling hurricanes can have significant economic value given the estimated cost of $1 million to evacuate a linear mile of coastline.

The first phase of the SBIR grant is focusing on the technical feasibility of the system and functional specifications that will guide prototype development in the second phase. Several engineering and scientific challenges will be addressed using design-simulation cycles to study tradeoffs of system components and develop realistic cost estimates given the feasibility analyses. The conference presentation will highlight results from the first phase of the project including recommendations on the most cost-effective and practical probe deployment strategies for different applications. It will conclude with plans for prototype development and observing system simulation experiments that gauge data impact compared with current and planned observing systems for severe storm and hurricane prediction.