The LVST what it is and how it works

• Direct and indirect detection ?

The radar waves broadcast by Graves Space radar cannot be received directly by the LVST receiver because the curvature of the Earth has Dijon below the horizon as viewed from Lowestoft (which is both North and west of Dijon). The LVST receives bursts of indirect radio waves when the transmitted wave is reflected by an object which is opaque to radar and above Lowestoft' south eastern horizon . This could be an aeroplane, a satellite or more often than not an electron plasma trail created by a meteor.

• Back scatter and forward scatter?

The Graves Space Radar is designed to broadcast its signal primarily south so the reflected signal received by the LVST in Lowestoft should be the result of reflection or 'back scatter' from meteor trails south of Dijon. However, there is some evidence that the screening at the back of the transmitters allows some of the radar signal to leak northwards. The consequence might be that the LVST receives some 'forward scatter' bursts from meteor trails between Dijon and Lowestoft. Clearly the power of the leaked signal will be less than that for the primary signal but the meteor trails detected by 'forward scatter' will be nearer to Lowestoft than those detected by 'back scatter' with a resultant and opposite impact upon signal strength.

• What does the LVST detect?

The LVST detects the Graves signal after it has been reflected by a body both opaque and reflective to radio waves having a frequency of 143050 kHz. and which exists within altitude, range and geometric parameters. Such objects include aeroplanes, ionised meteor trains, satellites, the ionosphere (subject to meteorological conditions) and the Moon. In addition, like all radio receivers the LVST receives constant and sporadic interference (or background noise) from terrestrial and non terrestrial sources.

As in most forms of astronomical investigation, separating the 'signal' from 'noise' in LVST observations is a difficult and ongoing task.

• Under dense (U), Over dense (O) and Transition (T) meteor trails ?

Scientists classify meteor trails into 2 classes based upon the ionisation (electron) density of the trail core. An accepted definition is as follows:

"Under dense trails have low electron density q<1014 electrons/metre and the scattering is done by individual electrons. These trails are formed by micro meteors with masses from 10-5 g to 10-3 g. 90% of echoes are underdense, with durations of tenths of a second.

Over dense trails have electron density of q >1014 e/m and fully reflect the incident wave as the trail is treated as a cylinder reflector. 10% of events arise from over dense conditions and last for a few seconds". Detection & Analysis of Meteors by RADAR (Using the GRAVES space surveillance transmitter) by Dr David Morgan 2011

www.britastro.org/radio/projects/Detection_of_meteors_by_RADAR.pdf

Transition meteor trails are more difficult to identify. They probably belong to the 'over dense' O group but decay quickly like an 'under dense' U group meteor trail. This may be because the trail is at such a high altitude and the diffusion so fast that there is insufficient time to reach the initial radius required for it to exhibit over dense behaviour.

The statistical approach to classification of observations is open to debate. The method used in analysis of data collected by the LVST is set out alongside the published tables and graphs. A consistent approach will be adopted year on year and for the analysis of main meteor showers in order that relative assessments might be made.

• What is Spectrum Lab ?

Meteors rain down on the Earth 24/7 and 365 days a year.Spectrum Lab is a free software application designed to help users capture and analyse the spectrum of an audio signal via a PC's soundcard and apply audio filtering operations. Spectrum Lab runs 24 hours - 365 days a year at the LVST capturing reflected signals from the Graves Transmitter.

For each reflection event the following information is collected:

1. Maximum noise amplitude over a range of frequencies
2. Maximum signal amplitude
3. Frequency at maximum signal amplitude
4. Signal duration above trigger amplitude A(t)
5. Date
6. Time

• Spectrum Lab Analyser settings:

Max amplitude Noise A(n) in dB over frequency range: ( 950,3450) Hz

Max amplitude Signal A(s) in dB over frequency range: : (1950,2450) Hz. - Centred (f) = 2200 Hz with a 500 Hz spread.

Capture trigger amplitude A(ts) = A(n) + 15.