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Lightning Detection
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ITU studies have determined that the optimal frequency for long-distance Arrival Time Difference (ATD) lightning detection systems is 9.76 kHz. However, the currently-operating ATD system uses the frequency 13.733 kHz due to interference near the 9.76 kHz frequency.
According to the ITU:
"Long-range lightning detection using observations near 10 kHz has been performed since 1939, originally with a very manpower-intensive system measuring the direction from which signals were received, but since 1987 detection has been carried out with an automated Arrival time difference system (ATD) using the time differences of signals received to derive strike locations.
"The ATD system utilizes a network of “detector” out-stations to monitor spectral emissions of cloud to ground lightning strikes centred between about 5 and 20 kHz. At these frequencies the sky waves, reflected off the ionosphere, propagate for very large distances with relatively little attenuation and are preceded by a ground wave at shorter ranges. Thus, it is possible to receive the emissions from the cloud to ground strokes at thousands of kilometres from the stroke location. A distributed network of ground based sensors can locate the origin of the lightning stroke, using the time differences between the arrivals of the lightning emission at the individual sensor sites.
"At June 2010, the network comprised 11 sensors distributed across Europe from Iceland to Cyprus, operating in collaboration with Finland, France, Germany, Iceland, Ireland, Portugal and Switzerland."
At the 2012 World Radiocommunication Conference, the use of the band 8.3 - 11.3 kHz for passive meteorological aids service (i.e., ATD lightning detection) was noted, formally extending the table of frequency allocations below 9 kHz.
In FCC 15-50 (2015), the FCC has proposed to adopt the 8.3-11.3 kHz MetAids allocation in the U.S.
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Frequency Bands |
| Band | Use | Service11 | Table |
| 8.3 - 11.3 kHz | WRC-12 allocation for lightning detection | Meteorological Aids | - |
Frequencies |
| Frequency | Bandwidth | Use | Service | Table |
| 9.76 kHz | - | Optimal frequency for Arrival Time Difference (ATD) lightning detection | Meteorological Aids | - |
| 13.733 kHz | - | Operational ATD long-range lightning detection system | Meteorological Aids | - |
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