The calibration of a parabolic antenna with the aid of closer-range photogrammetry and surveying
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Abstract
In recent years, closer-range photogrammetry and surveying have been applied in many industrial applications to analyse complex shapes. In particular, these two mensuration techniques have been applied to antenna reflector calibration, receiving widespread acceptance. The purpose of this report is to investigate the suitability of non-metric analytical photogrammetry for reflector antenna calibration through the comparison of results with those obtained using precision surveying with electronic theodolites.
This study begins with an examination of the requirements for the calibration of reflector antennas. A one-meter parabolic weather satellite reflector was evaluated in this investigation. The planning and preanalysis considerations for both photogrammetry and surveying are discussed. Since the data acquisition and reduction techniques differ for each method, analytical close-range photogrammetry is further examined.
With the assistance of three software packages designed for non-metric photography, object space coordinates were determined the reflector antenna. The bundle adjustment programs UNBASC2 and GEBAT-V as well as the Direct Linear Transformation with Data Snooping were evaluated and compared.
The computed object coordinates were used to determine, using the method of least squares, the best fitting paraboloid which defines the parabolic reflector under consideration. An evaluation of the surface parameters and deviations from the ideal paraboloid are considered in the final calibration. SAS/GRAPH software was used to provide a 3-dimensional representation of the surface and detected deviations.
The results of this investigation illustrate that closer-range photogrammetry can be used to accurately determine spatial coordinates for the purpose of calibrating reflector antennas. Furthermore, the potentials and limitations of non-metric imagery have been observed and recommendations for its use in industrial applications are proposed.