Andrew McGrath's PhD Thesis

 

An Erbium:Glass Coherent Laser Radar for Remote Sensing of Wind Velocity

Flinders University of South Australia, School of Earth Sciences
August 1998
  • Preliminaries: Abstract, declarations and table of contents
  • Chapter 1: Introduction
    How to measure wind, and the principles of lidar
  • Chapter 2: Performance Analysis
    Atmospheric and lidar system modelling
  • Chapter 3: Software System Description
    Algorithms and system architecture, with an introduction to software engineering
  • Chapter 4: Development of Laser Transmitter
    Injection-seeded, Q-switched Er:glass laser transmitter/receiver
  • Chapter 5: Field Trials
    The first velocity measurements with an Er:glass CLR
  • Chapter 6: Conclusions
  • Et cetera: Appendices and References
    Appendix A: modelled performance animations
    Appendix B: Source code
    Appendix C: Applied Optics Paper
Email me if you want access to the source code or SNR calculator (Win 9x executable)

Abstract

Remote sensing of wind fields has important applications in meteorology, air safety and other areas. Various methods have been developed for such sensing, and pulsed Doppler lidar is one of the most exciting and promising of these.

For various reasons, operation of a wind-sensing lidar at a wavelength of 1.5µm has some advantages over wavelengths that have been used before now. Erbium-doped glass lasers operate at this wavelength and additionally have the potential advantage of the use of components for telecommunications equipment, which also employ erbium lasers. Lasers of this type have not previously been shown to operate with suitable characteristics for use in a pulsed Doppler lidar system. It was the aim of this project to develop such a lidar, using an Er:glass laser system to measure winds using the Doppler shift of light backscattered from atmospheric aerosols.

A performance model was developed and used to verify the suitability of a system with the expected parameters for wind sensing. Such modelling also provides a clear indication of which parameters have significant effects on system performance and which do not. A system control and signal processing software package was developed to control the collection of lidar data and process the atmospheric return signals into profiles of wind velocity versus range. This software package is intended not only for use with the concept demonstration system developed by this project, but also with successors to this system.

The transmitter for the lidar system was built and characterised as an injection-seeded, Qswitched, flashlamp-pumped Er:glass laser suitable for coherent remote sensing. A diffraction grating was used as a frequency-selective element in the slave resonator to permit matching to the seed wavelength in order to achieve injection seeding. This laser produced pulses of 1 to 2mJ energy and 400ns length, with transform-limited spectral line width. Field trials of the lidar system resulted in the Doppler measurement of the velocity of a moving hard target, but the difficulties encountered in the field precluded the system optimisation necessary for wind sensing.

My supervisors for this work were Dr. Jorg Hacker (Flinders University) and Prof. Jesper Munch (Adelaide University).
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