Head and trail echoes in radio meteor scatter
In meteor scatter, the head echo is the radar reflection from the plasma region immediately surrounding the meteoroid itself as it travels through the atmosphere — essentially, the “glowing ball” of ionized gas right at the meteor’s front.
Here’s a breakdown of what that means:
🔹 1. The Two Main Radar Echo Types
When a meteoroid enters the atmosphere, radar can detect two distinct echoes:
| Type | Origin | Duration | Doppler Shift | Typical Use |
| Head Echo | From the ionized plasma immediately surrounding the meteoroid’s body | Milliseconds | Very high (because it tracks the meteor’s actual velocity) | Used in scientific radar studies (e.g. CMOR, MU radar) |
| Trail Echo | From the ionized column left behind | Up to several seconds | Stationary (after the meteor passes) | Used for forward-scatter communications (e.g. 50.408 MHz beacons) |
🔹 2. Physical Explanation
As the meteoroid compresses air in front of it, the temperature rises enough to ionize atmospheric molecules and create a small, dense plasma envelope.
That plasma reflects radio waves strongly but briefly, and because it moves at 11–72 km/s, the reflected signal is Doppler-shifted across a wide frequency range.
In contrast, the trail echo is reflected from the long, cooling ionization path that remains after the meteoroid has passed. That’s the one typically picked up in amateur meteor scatter setups.
🔹 3. Detection Context
- Head echoes are mainly observed by high-power, high-gain pulsed radars (e.g. the Canadian Meteor Orbit Radar or Jicamarca radar).
- They are used to determine meteoroid trajectories, masses, and ionization cross-sections.
- Amateur 50 MHz forward-scatter systems (like GB3MBA → receiver links) generally do not detect head echoes, only the trail echoes, because the radar power and geometry are different.