An investigation of the structure of the Southern Hemisphere radio-meteor streams
- Authors: Roux, David Gerhardus
- Date: 1988
- Subjects: Radio meteorology -- Southern Hemisphere , Solar system
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5448 , http://hdl.handle.net/10962/d1004587 , Radio meteorology -- Southern Hemisphere , Solar system
- Description: Our current knowledge of the Solar System, with a particular emphasis on the systems of interplanetary objects, is reviewed, and the theory of meteors and the reflection of radio waves from meteoric ionization is then discussed. A description of the meteor radar is given and a method of calibrating the antenna beam is developed. The main project comprises two parts: (a) A general survey of the radar echorate for 20 major and minor meteor streams and the sporadic meteor background, conducted from Grahamstown over the period 1986 April to 1988 January, is described. Definite shower activity was observed for all of the major and some of the minor showers. (b) Based on a scheme proposed by previous workers (Morton & Jones), a method of recovering meteor radiant distributions from the distribution of echo directions is developed. We devise a technique of compensating for possible distortions of the resulting radiant maps, which may arise due to the arisotropic antenna beam. This involves a system of echo-weighting. Radiant maps which showed considerably less distortion than those of the above workers were obtained without the weighting procedure. It is concluded that, although the method in its present form introduces spurious features into the maps, the principle is sound and should eventually be refined to produce the desired compensation
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- Date Issued: 1988
The establishment of a Lidar facility at Rhodes University
- Authors: Grant, Richard Peter James Seton
- Date: 1988
- Subjects: Optical radar , LIDAR , Receiver , Transmitter , Photon counting electronics , Aerosol scattering , Temperature profiles , Stratosphere
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5445 , http://hdl.handle.net/10962/d1001998
- Description: LIDAR is the optical equivalent of RADAR. A LIDAR facility has been established at Rhodes University using a flashlamp-pumped dye laser as the transmitter and a photomultiplier tube at the focus of a searchlight mirror as the receiver. The setting up of the receiver and transmitter as well as the design and construction of the photon counting electronics is described. The LIDAR has been used to measure aerosol scattering ratios and temperature profiles in the stratosphere and these results are presented with the algorithms and software used to reduce the data. Finally some recommendations are made for future work
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- Date Issued: 1988
The selection and evaluation of grey-level thresholds applied to digital images
- Authors: Brink, Anton David
- Date: 1988
- Subjects: Image processing -- Digital techniques
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5443 , http://hdl.handle.net/10962/d1001996
- Description: Many applications of image processing require the initial segmentation of the image by means of grey-level thresholding. In this thesis, the problems of automatic threshold selection and evaluation are addressed in order to find a universally applicable thresholding method. Three previously proposed threshold selection techniques are investigated, and two new methods are introduced. The results of applying these methods to several different images are evaluated using two threshold evaluation techniques, one subjective and one quantitative. It is found that no threshold selection technique is universally acceptable, as different methods work best with different images and applications
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- Date Issued: 1988