Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602612
Title: Simultaneous photographic and radio echo oberservations of meteors
Author: Davis, John
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 1959
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Abstract:
A programme of simultaneous photographic and radio echo observations of meteors is described. The author has been mainly concerned with the photographic aspects of the programme and a detailed description of the problems involved in the operation of meniscus Schmidt cameras is included. In particular, a new method of sensitising the steeply curved focal surface, characteristic of these instruments, is described. A critical analysis of the sensitivity of the photographic system is given. An angular measuring instrument and microphotometer have been designed and constructed in order that the spherically curved photographic plates may be measured directly. These instruments result in a considerable saving in analysis time when compared with the American technique of copying the plates onto a flat surface for measurement in conventional instruments. The techniques developed for the computation of the position of a meteor trail, and the velocity and brightness of a meteor, are described. Observations have been carried out over a period of zt years and a total of 75 meteors have been photographed. 18 of these meteors have radio echoes assooiated with them. One of the correlated observations, of a bright Geminld meteor, has enabled the attachment coefficient of eleotrons to neutral oxygen molecules to be determined. It has been found to be an order of magnitude greater than the theoretical estimate which has been the only value available until now. An attachment coefficient of this order is shown to explain the departures of radio echo observations of meteors from the simple diffusion theory. For example, it is shown that an attachment coefficient of this order will limit the maximum possible echo duration from a meteor trail to a few hundred seconds, instead of several hours which might be expected on diffusion theory. It will confine the echoing region on a meteor trail to a narrow height range and cause a departure of radio echo observations from the A duration law. These are well established observational facts. 53 colour indices have been derived from the observations. A dependence both on velocity and magnitude is found, the latter being the greater. The results are in agreement with those obtained with the American Super Schmidt cameras but the interpretation is questioned. The variation in colour index is explained qualitatively in terms of observational effects due to the visual magnitude estimates and to real changes in the meteor spectrum. In view of the observational effects on visual estimates of brightness it is suggested that the photographic magnitude scale should be made the standard to which observations are related. A relationship between the absolute photographic magnitude and the luminous intensity in the photographic spectral range is derived. The dependence of the ratio of luminosity to ionisation upon brightness and velocity is investigated. No significant brightness dependence is found. The velocity dependence of the ratio of luminous intensity to electron line density is established. The velocity dependence of the luminous and ionising efficiencies, and of the probability of ionisation, are found. The relative values of the efficiencies have been derived from the present data although it is not possible to determine their absolute values. A relationship between the absolute photographic magnitude and the electron line density is determined. The relationship involves a velocity index and this is tabulated with the estimated uncertainty in its value. Some suggestions for future observations are included.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.602612  DOI: Not available
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