GlobalSense: A New Environmental Sensing System Based on Large Ensembles of In Situ, Airborne Probes

This paper will present results from a National Science Foundation Small Business Innovation Research (SBIR) grant to develop prototypes of a new observing system, known as “GlobalSense”, which features an ensemble of completely disposable, airborne probes, mechanisms to deploy probes, and receiver platforms to gather data from probes. The GlobalSense probes will make measurements as they drift passively through the air with no active propulsion or flight.

The GlobalSense probe design will exploit miniaturization as well as integration of micro sensors, power sources, and other micro- and nanotechnology-based components to minimize complexity, cost, size, mass, terminal velocity, and power consumption yet still provide accurate measurements compared with currently accepted observing technology. With low enough mass and an aerodynamic shape based on bio-inspired designs (e.g. dandelion seeds), GlobalSense probes will be designed to remain airborne for hours or longer depending on atmospheric conditions.

The GlobalSense probe target mass is less than 1 gram with size on the order of centimeters. In addition to minimizing fall speed, these specifications also greatly reduce hazards to people or property as probes drift through the air. One potential concern is the environmental impact caused by the probes once they settle on land or water. The GlobalSense probes will not contain materials or components including power sources that pose any significant mechanical, electrical, or environmental hazards. Ultimately, GlobalSense probe components would be biodegradable but significant advances in materials science and organic electronics will be needed to achieve this design goal.

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 probes will leverage research and development on sensor-driven microsystem design to achieve the vision for ubiquitous sensing of the atmosphere. 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 GlobalSense probes will include a microprocessor unit, radio frequency transmitter, power source, antenna, interface electronics, packaging, and micro sensors to measure ambient air temperature, relative humidity, pressure, and velocity. The proliferation of cell phones, navigation units, and other devices has driven the size and power requirements of micro global positioning system chips to the point where they can be leveraged to provide onboard probe velocity and three-dimensional position measurements.

Communication will feature ultra-low power transmission (-20 dB) directly from probes in discrete data packets that can be detected by receivers using forward error correction combined with time division time-division multiple access and frequency-division multiple access communication schemes. The fixed or mobile receiver platforms will contain hardware and software to decode data packets from multiple probes within range and store or retransmit the information to other locations. Probes could be deployed from aircraft or as payloads on weather balloons to leverage existing infrastructure and provides a means to release them at different altitudes. Releasing probes in clusters will provide significant redundancy in the event of a single probe component malfunction or failure.

The initial GlobalSense application is improving weather analysis and forecasting by greatly expanding the time and space density of 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.

Two areas that could benefit from the GlobalSense system are severe storm and hurricane forecasting. The National Oceanic and Atmospheric Administration (NOAA) Warn-on-Forecast (WoF) initiative is designed to extend tornado warning lead-time beyond the plateau reached using Doppler radars. A key challenge of the WoF initiative is to measure low-level boundary layer fields at space and time scales that are not feasible with any current in situ or remote sensing platforms. GlobalSense probes would be ideal to provide these observations for studying the initiation and evolution of supercell thunderstorms. The end goal would be to integrate these data into numerical weather prediction models and increase the lead time for severe weather resulting from such storms.

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 NOAA routinely flies operational and research aircraft reconnaissance missions into Atlantic hurricanes, there are significant opportunities to provide 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 (e.g. 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 first phase of the SBIR grant focused on the technical feasibility of the GlobalSense system and functional specifications that will guide prototype development. The conference presentation will highlight results from initial efforts to build and test probes as well as receivers using commercial-off-the-shelf components. It will conclude with plans for testing a complete prototype GlobalSense system in the atmosphere featuring hundreds of probes released from balloons over east, central New York State in the summer of 2015.