Meteor burst communications

Lore & Background

The earliest direct observation of meteors affecting radio propagation was reported in 1929 by Hantaro Nagaoka. In 1931, Greenleaf Pickard noticed bursts of long-distance propagation during major meteor showers, while Bell Labs researcher A. M. Skellett suggested that oddities in night-time radio propagation were due to meteors. The following year, Schafer and Goodall noted atmospheric disturbances during the Leonid meteor shower, leading Skellett to propose reflection or scattering from electrons in meteor trails. In 1944, James Stanley Hey confirmed that meteor trails reflected radio signals while researching a radar system aimed at detecting V-2 missiles. In 1946, the US Federal Communications Commission found a direct correlation between VHF signal enhancements and individual meteors. Studies in the early 1950s by the National Bureau of Standards and Stanford Research Institute had limited success in using this medium.

The first serious effort was the Canadian Defence Research Board's project JANET in the early 1950s, which sent pre-recorded data bursts from Prince Albert, Saskatchewan to Toronto over 2000 km. It became operational in 1952 and continued until about 1960. The COMET system (Communication by Meteor Trails) became operational in 1965 for NATO's Supreme Headquarters Allied Powers Europe, linking the Netherlands and France with average throughput between 115 and 310 bits per second. Interest waned with satellite communications in the late 1960s, but revived in the late 1970s when satellites proved less useful at high latitudes or where signal security was needed. The U.S. Air Force installed the Alaska Air Command MBC system in the 1970s, though its operational status is not publicly known. The Alaskan Meteor Burst Communications System (AMBCS), a DARPA-funded testbed by SAIC, used phase-steerable antennas to achieve average data rates of 4 kbit/s.

Reader's Guide

Meteor burst communications provided a unique, low-cost alternative to satellites for long-range data links, particularly in remote or high-latitude regions. The SNOTEL system of the United States Department of Agriculture used meteor scatter for over 40 years to collect snow water content data from over 500 remote stations in 11 western states, polling groups of about 60 stations in an average of 5 minutes. This system was discontinued in 2023. In amateur radio, meteor scatter communication is conducted using precise schedules of transmission and reception, with stations repeatedly sending the same information until acknowledged. Single sideband voice and Morse code were historically popular, but since 2000 digital modes like MSK144 (implemented in WSJT-X software) have become dominant. The technique's reliance on unpredictable, brief ion trails means that complete exchanges often require multiple meteors over extended periods. Theoretical gains from real-time steering of antennas to pinpoint ion trails have not been experimentally tested.

Did You Know?

• Meteor trails used for communication persist for only fractions of a second to a few seconds.
• The COMET system for NATO achieved average throughput between 115 and 310 bits per second.
• The USDA's SNOTEL system used meteor scatter for over 40 years until 2023.

Fundamental Wave Behaviors and Free-Space Physics

Radio waves, as a form of electromagnetic radiation, interact with their surroundings through several key phenomena: reflection, refraction, diffraction, absorption, polarization, and scattering. Understanding how varying atmospheric conditions affect these interactions is critical for a wide range of practical applications, from choosing frequencies for amateur radio communications to designing reliable mobile telephone systems, radio navigation networks, and radar operations. In a vacuum, radio waves travel at the speed of light, and the Earth's atmosphere is thin enough that propagation in air closely approximates this velocity. However, variations in atmospheric density and temperature introduce slight refraction, or bending, of waves over long distances. In free space, the inverse-square law governs power density: doubling the distance from a point-source transmitter reduces received power density to one-quarter, while each field component—electric and magnetic—drops by half. This fundamental geometric relationship underpins the design of every radio communication system.

Line-of-Sight and Direct-Path Transmission

Line-of-sight propagation describes radio waves traveling in a straight line between transmitting and receiving antennas, a mode often called direct-wave. It is the dominant mechanism at VHF and above, and the only viable propagation mode at microwave frequencies and beyond. On Earth's surface, the visual horizon constrains this range to roughly 40 miles (64 km), though accurate calculations must incorporate atmospheric refraction and frequency-dependent attenuation caused by precipitation and water vapor. This mode powers cell phones, cordless phones, walkie-talkies, wireless networks, FM and television broadcasting, radar, and point-to-point microwave relay links. Satellite communication extends line-of-sight paths to extraordinary lengths: home dishes receive signals from satellites 22,000 miles (35,000 km) aloft, and ground stations maintain links with spacecraft billions of miles from Earth. At VHF frequencies, ground-plane reflection adds a notable complication, as interference between the direct beam and its ground-reflected counterpart yields an effective inverse-fourth-power distance law rather than the simpler inverse-square relationship.

Ground Wave and Surface Propagation

At lower frequencies spanning the MF, LF, and VLF bands—roughly 30 to 3,000 kHz—vertically polarized radio waves behave very differently from their higher-frequency counterparts. Rather than traveling in straight lines, these waves interact with the conductive surface of the Earth, effectively clinging to it and following the planet's curvature. This ground wave or surface wave propagation allows signals to bend over hills and other obstacles via diffraction, reaching listeners well beyond the visual horizon. AM broadcast stations and amateur radio operators rely on this mechanism to cover their service areas. As frequency decreases further into the VLF and ELF ranges, attenuation with distance diminishes significantly, enabling truly worldwide communication. These very low and extremely low frequency waves can penetrate substantial distances through water and earth, making them indispensable for mine communication and for reaching military submarines submerged beneath the ocean surface.

Skywave Propagation and Supplementary Mechanisms

At medium wave and shortwave frequencies in the MF and HF bands, radio waves encounter the ionosphere, a layer of charged particles situated high in the atmosphere. When transmitted at an angle into the sky, these waves are refracted by the ionized layer and bent back toward Earth, sometimes at transcontinental distances far beyond the horizon. This skywave propagation mechanism forms the backbone of international shortwave broadcasting and enables amateur radio operators to establish contacts with stations in distant countries. Beyond these primary modes, several less common propagation mechanisms supplement communication: tropospheric scattering, or troposcatter, and tropospheric ducting operate at VHF frequencies, while near vertical incidence skywave, known as NVIS, provides HF coverage within a few hundred miles when conventional skywave paths are impractical. Together, these diverse propagation modes ensure that radio communication remains viable across virtually every distance and frequency band.