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As of the first of May 2024 - the LVST is back on line.
The limits of statistical analysis, correlation, causality, absolute and comparative information:
The limits of statistical analysis, correlation, causality, absolute and comparative information:
Causal relationships cannot be established by statistical means alone but sometimes it is possible to establish correlations between observations of variable quantities. Even apparent interdependence of variable quantities comes with a margin of error.
The following limitations regarding the information gathered, analysed and published here should be considered:
- The hardware used, set up and operation of the LVST is both basic and simple.
- The data obtained by the LVST is system limited and relates to radar reflections from electron trails associated with meteors not the meteoroids themselves.
- Meteor trails have fluctuating electron densities which change over time and complicate the interception and reflection of pulsed radar waves.
- The Spectrum Lab software used for capturing individual meteor trails is set to trigger data capture only when the amplitude of the signal exceeds the maximum amplitude of noise (monitored across a wide frequency range) by 15 db. The meteor trails captured are therefore less than the total number that occur in the area of the atmosphere being monitored and as the maximum amplitude value for noise varies so does the trigger amplitude value for the signal.
- The Graves transmitter-LVST receiver system can only detect a limited set of the total number of meteor trails that occur globally over any set period of time in the Earth's atmosphere. This is due to the local nature of the system's observations as well as any short falls in its efficiency. Wherever possible a large sample has been used for analysis to increase the probability that sample observations are representative of the global set.
- It is very difficult to distinguish between 'Under dense U' and 'Over dense O' meteor trails. The difficulty is caused in part by 'Transition meteor trails T' which have the electron density of an 'O trail' but the very short duration of a 'U trail'. In plotting statistical graphs U+O includes all observations including T. U+T is the set of U observations including T but excluding O. O-T is the set of O observations excluding T and U.
- The LVST was set up at the Jodrell Plank Observatory to enable comparisons to be made between meteor activity on an hourly, daily and annual basis. In particular the system has been kept running to investigate the year on year behaviour of meteor showers on a comparative rather than absolute basis.
Calculation of radial velocity using 'doppler shift'.
Calculation of radial velocity using 'doppler shift'.
Velocity is a vector and meteor plasma trails, moving in 3 dimensions as they travel through the atmosphere, have measurable velocity.
To quote from the film 'Despicable Me' - " Vector - having both direction and magnitude".
The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point. That is, the radial (or Line of sight - LOS) velocity is the component of the object's velocity that points in the direction of the radius connecting the object and the point.
The LVST is able to measure the 'doppler shift' in frequency of the reflected signal. The radial velocity V of the meteor trail may be calculated using the formula:
V = c (Δf)/F
where:
Δf is the change in frequency (Max Frequency at which the signal amplitude is at maximum - 2000 Hz)
F is the transmitted frequency from GRAVES (143050000 Hz)
V is the radial or LOS (between the meteor train and Lowestoft) velocity of the trail
C is the speed of light (300,000,000 m/s)
Note that the radial velocity of the meteor trail V is not the velocity of the meteoroid as it enters the the Earth's atmosphere. The former is a line of sight component the latter is not. The meteor trail and the meteoroid behave differently and have magnitudes that may be a factor of ten or more apart. The Perseids enter the Earth's atmosphere at speeds ranging from 11 to 72 km /sec. The mean radial velocity calculated using the 'doppler shift' method and the LVST 2016 Perseid reflection observations is +0.367 km/sec.
Observations having a negative (-) radial velocity may be considered as moving away from the LVST and those having a positive (+) radial velocity as moving towards.
Software used at the Jodrell Plank Observatory in the capture and Analysis (of data)
Software used at the Jodrell Plank Observatory in the capture and Analysis (of data)
- Spectrum Lab
- Excel
- INZight for Data Analysis (R programming language)
For help with software and difficult sums, thanks to Prof Chris Wild and his Team at the Department of Statistics, The University of Auckland, New Zealand and Open University Future Learn.
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