Meteors
Every day, tonnes of dust grains hit the Earth’s atmosphere at a few tens of kilometers per second. Most burn up on the way down, but a few thousand tonnes land on the Earth each year as micrometeorites .
A collection of micrometeorite grains collected from rooftops by Project Stardust.
The largest of these are smaller than 1 mm
Radio Meteors:
As the dust passes through the upper atmosphere, around 85-105km from the ground, the heat vaporizes surface atoms from the meteor, creating an ionized trail 10- 50km long. A passive meteor radar can detect the trails produced by this space dust by detecting the radio waves that bounce off the ionized gas. The radar cross section of the trail of a sand grain can be as large as a battleship!
As the ionized plasma explodes away from the path of the meteor at high velocity, the reflected radio waves are doppler shifted above and below the frequency of the transmitter providing illumination. This doppler shift makes the signal reflected off the meteor trail visible at the receive site. The degree of doppler shift relates to the energy of the meteor; velocity and/or mass.
This image shows many radio meteor signatures in 3 different ways. Software used here are Argo, Spectran, and HDSDR.
Argo is seen on the left. It produces a 7 minute strip chart flowing from right to left with vertical lines representing meteor detections.
Spectran is seen top right. It produces a 1 minute strip chart flowing from top to bottom with horizontal lines indicating meteors,
Behind them is HDSDR, an SDR receiver application that shows about a 7 second strip chart on the bottom right flowing upward. At the moment of capture there was only one faint meteor visible but here they would also appear as horizontal lines.
The image was captured on a laptop with a 15" screen requiring some compromises to enable all the display mechanisms to be seen simultaneously. [Would like to embed a video to show a typical live moving display]
Counting Meteors:
Networks of Citizen Scientists participate in the global collection of radio meteor counts. One such organization is the Radio Meteor Observing Bulletin. The image above is a sky map that is color coded for meteor counts that was produced using their software. RMOB provided software for making counts if you have a receiver.
The map above shows the currently active RMOB observers in North America (For the full list go here: https://www.rmob.org/ and select Live Observations). Individual observers have automated observing systems. that post daily counts.
An individual observer's counts look like this:
Top left tells about the observatory, lower left plots hourly counts for the current day. Right side plots a color coded heat map of daily counts for the month. The above was a posting for June 12 so most of June is blank.
Here at VBAS when we transition to 24/7 Meteor Radar operations we intend to participate in this network.