A portable radio-acoustic sounding system for vertical temperature profiling within the boundary layer

Abstract

Remote temperature profiling has been a well-researched topic in recent decades, with systems capable of measuring into the upper troposphere; these are large units that are either fixed at dedicated sites, or require vehicular means of transportation. The aim of this thesis was to develop a portable radio-acoustic sounding system for vertical temperature profiling within the boundary layer. To achieve this, three objectives were identified: modelling and simulation, design/prototyping and experimental validation as a proof-of-concept. Modelling and simulation was carried out to firstly characterise the proposed system. Phenomena such as atmospheric attenuation and the Bragg effect were then investigated and quantified. From this, the expected radar cross section, and therefore backscattered signal power, was quantified as a function of height. This was used as a basis for the physical prototype. The prototype was based upon a novel composite antenna design, in which an acoustic emitter is fixed in the centre of the parabolic antenna used for radar transmission and reception, thus achieving colocation of the two "beams". This antenna is driven by specially-developed Doppler radar operated at 2.45 GHz, with an acoustic frequency of approximately 5.6 KHz. Signal processing has been implemented using National Instruments hardware/software. The complete system occupies an area less than 1 m2 and can be carried by a single person. The Doppler radar and signal processing was tested and proven to measure velocity profiles of a solid object. Initial testing with the composite antenna generated no significant results as correct alignment was not possible due to time constraints. Therefore the parabolic dish was removed to only use the feed antenna, eliminating alignment uncertainties. Results from this testing show evidence of microphonic radar returns, however there is no sign of backscatter from the acoustic wavefront, which is needed to measure temperature. Future work is needed to correctly align the parabolic antenna so this can be used to its full ability in testing. A more directional speaker could be sourced with a larger sound pressure also to create a larger radar cross section. These would both contribute to greater return signal strength, thus making temperature measurements possible.