Author(s):
Martin Füllekrug - Department of Electronic and Electrical Engineering, University of Bath
In 1925, Scottish physicist and Nobel Prize winner Charles Thomson Rees Wilson predicted that an electrical breakdown of Earth’s atmosphere occurs above thunderstorms. The electric field that forms between thunderclouds and the atmosphere can cause huge bursts of energy to arc upward through the electric field, causing the surrounding air to glow. Scientists have only recently determined the significance of these transient airglows, commonly referred to as “sprites.”
Occasionally, high-energy cosmic particles ionize air molecules and produce free electrons in the atmosphere. Recent simulations suggest that when these free electrons coincide with the intense electric fields generated by powerful lightning discharges, narrow beams of electrons are accelerated upwards into near-Earth space. Effectively, the sprites are powering giant particle accelerators 40 km above Earth’s surface.
Sprites are difficult to study because they are much less common than lightning bolts and last only a fraction of a second. To uncover experimental evidence of these natural particle accelerators, our team built a flexible system to monitor the radio waves emitted by the particle beams.
Requirements
To maximize the scientific return of our research project, it was critical that the monitoring system perform continuous, high-quality digital recording and be portable and modular.
Because the natural environment changes rapidly, continuous recordings offer higher probability for acquiring key data points. If the system detects a novel event, we need to access and analyze historical data before and after the event takes place.
Portability is critical in monitoring environmental characteristics in remote locations. Ideally, the installation of the system needed to be independent of existing infrastructure, such as main power supplies. Consequently, the monitoring station had to operate at extremely low power and be lightweight.
Implementation
With these requirements in mind, we focused on developing an environmental monitoring system that consists of the following components:
- An electric field sensor with analog signal conditioning circuitry
- An NI USB-6251 DAQ module
- A high-precision clock
- LabVIEW graphical system design software on a low-power data processing unit
With the flexibility and modularity of NI products, we fully customized the monitoring system rather than conforming to vendor-defined functionality. As a result, we implemented unique features and functionality to more easily realize our project goals.
The integrated screw terminals on the front end of the NI USB-6251 DAQ module simplify the integration of our sensitive electric field sensors. The multifunctional device facilitates continuous data logging and acquisition with aggregate sampling rates in excess of 1 MHz with maximum accuracy of 10 to 15 µV, is powered by a 12 V battery, and consumes 12 to 14 W of power.
The Navsync CW46 GPS sensor provides external sample timing for the data acquisition unit. The CW46 triggers individual sample acquisition at a rate of 1 MHz. It runs on USB and consumes 2.4 W of power. LabVIEW and Windows Embedded run on a Cranberry SC20 Smart Client processor to stream the recorded data continuously to a mass storage medium. The SC20 is powered by a 12 V battery and consumes 6 W of power.
The environmental monitoring system records radio waves with 450 kHz maximum bandwidth, 10 µV precision, and 10 ns temporal resolution while maintaining a total power consumption of 25 W.
Benefits of the NI Solution
With the scalability of LabVIEW, the system’s functionality will evolve along with our requirements. For example, if we need to implement advanced inline analysis of the acquired radio waves, it is easy to modify the existing LabVIEW code to meet that need.
We also can use the system’s modular architecture to upgrade the hardware to incorporate future technological advances and extend the frequency range with minimal impact to our LabVIEW application.
The NI DAQ hardware was fully compliant with the datasheet specifications and met all of our expectations for performance and implementation ease. In addition, the NI technical support team was highly responsive to our questions, which helped us build and deploy the solution within tight deadlines.
Conclusion
Our high-precision, low-power environmental monitoring system is now implemented at Exmoor National Park in the UK and at other remote locations across Europe to perform radio measurements of distant lightning discharges. The innovative solution has resolved the faint radio signals emitted by particle beams above thunderstorms, so we can acquire and analyze evidence of nature’s own particle accelerators.
We aim to use the system for industrial applications in the future as well. The National Physical Laboratory plans to implement the solution for high-precision timing applications to back up GPS timing for security applications.
Author Information:
Martin Füllekrug
Department of Electronic and Electrical Engineering, University of Bath
United Kingdom
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