April 5, 2013
EXCLUSIVE: Earth Networks – Tracking Lightning
Part 2 of redOrbit´s exclusive 6-part series
Alan McStravick for redOrbit.com - Your Universe Online
In the first installment of this series, we explored how the Maryland-based company Earth Networks positioned itself as the world leader in ground-based weather sensor data collection through the mass deployment of their weather station sensor network.
Typically, private sector weather companies like The Weather Channel or Accuweather rely on the National Oceanic and Atmospheric Administration (NOAA) for data collected via their network of satellites, radars and surface weather stations. Where Earth Networks stands apart is through their operation of the largest independent global sensor network. And the operation of this network was significantly improved with the addition of the Earth Network´s Total Lightning Network (ENTLN) only a few years back.
The company´s decision to monitor lightning was arrived at after decades of research on the subject indicated that an increase in the flash rate of intercloud (IC) lightning was predictive of imminent severe weather and possible tornadic activity. Robert Marshall, CEO and co-founder of Earth Networks, explained how NASA has employed the use of a lightning detection network at the Kennedy Space Flight Center in Florida since the 1970´s. However, the network they have utilized is a VHF network that, due to its limited geographic range, would be cost prohibitive to deploy on a large scale
While a cloud to ground (CG) lightning flash has a much more powerful amplitude, the challenge with detecting and measuring IC flashes exists due to their higher frequency and lower amplitude. It was only through innovation in the realm of measurement electronics that it became possible.
“The technology didn´t exist several years ago to do it until we did it,” Marshall told redOrbit. “The technology has changed so much in the last decade. There are a number of things that made this possible, what we do today, that was not possible 10 years ago,” he continued.
Marshall explained that each weather station is outfitted with two high-speed digital signal processors that record 24 million samples every second. Along with the ubiquity of Internet connectivity over the past decade and the low-cost associated with the production and deployment of each unit, Earth Networks quickly amassed the largest lightning sensor network on the globe. Currently, the company operates more than 700 units and expects to exceed 1,000 lightning sensors by the year´s end.
HOW A LIGHTNING SENSOR WORKS
redOrbit asked Marshall specifically about the impetus behind taking the company in the direction of focusing on lightning monitoring. “So, it´s really more about early warning,” Marshall replied. “The research indicated there is an opportunity for total lightning that looks really valuable. Strategically, several years ago, we were looking for what else we could add on to our weather stations to really give us some valuable data and allow us to develop some valuable products. What could we add to the basic weather station? And that´s when we came up with the lightning sensor.”
In order to understand how the ENTLN functions will require an example familiar to anyone who has ever listened to the AM band on their radio. During a thunderstorm, an AM radio within range of a lightning strike will be disrupted by crackling. This is due to the fact the AM band is amplitude based. The crackle is the AM band´s recognition of the passing electromagnetic pulse being emitted from the lightning flash, propagating out in all directions at the speed of light.
Much like the AM band, the lightning sensor is an antenna that is able to detect amplitude. The moment the electromagnetic wave hits the antenna, a sophisticated high-speed electronic array housed by the weather station measures the wave and transmits the data back to Earth Networks Germantown, Maryland facility.
As the wave travels out from the lightning strike it hits different lightning sensors at different times. Identifying a particular wave among several sensors in different locales allows the sophisticated algorithms used by Earth Networks to calibrate it and measure its strength.
In a particularly active thunderstorm, however, one might think it would be nearly impossible to distinguish one wave from another. Yet each wave presents its own shape signature, making it possible for Earth Network´s computers to identify each unique lightning through a process known as cross-correlation.
The genius of the ENTLN, however, is in what it does next. Once the wave has been registered by the antenna, measured and transmitted by the electronics array, the algorithm is able to use the data from multiple sensors to pinpoint the exact place on (or above) Earth via triangulation.
Comparing the method employed by ENTLN to current satellite technology, Marshall claimed, “A satellite can´t tell whether it´s a ground flash or a cloud flash or exactly where it is, but they are pretty good at figuring out there was lightning that happened in those spots.” The limitation to satellite technology, with respect to ENTLN, is that satellites utilize optical sensors. “The way we do it is very, very different,” concluded Marshall.
If ENTLN´s capabilities stopped at simply collecting the vast amounts of data it receives every second of every day, the network would be no less impressive. However, as Marshall mentioned previously, translating that data into real-time early warnings was the driving force behind the development of their total lightning network.
Counted among their clients are both private corporations and municipalities. Earth Networks provides them with a live weather product that collects data from the sensors and displays the information directly to them. City and county governments utilize this in order to better inform citizens in the immediate area.
Additionally, individuals who have the company´s app on their GPS-enabled smartphone receive the sensor data in the form of an alert when there is an increase in the rate of IC lightning in their area.
The name for their alert, Dangerous Thunderstorm Alert (DTA), was coordinated with the National Weather Service (NWS). This was done “to make sure we didn´t confuse the public because no private company really does this,” explained Marshall.
“The NWS is the official source for warnings. We didn´t want to call it a warning.” However, when a DTA is issued, it is because of the signature increase in lightning activity that often predicts an increase in high winds, hail and possible tornadic activity. Each alert is automatically generated by the system and updated every 15 minutes.
In the next installment in the series, we´ll explore the false alarm rates of ENTLN compared to NWS. Additionally, we will learn about a new visualization tool that promises to be beneficial to some of the more impoverished nations on Earth that are unable to implement a full radar system.